#### Migrating from GTK 3.x to GTK 4 [src]

GTK 4 is a major new version of GTK that breaks both API and ABI compared to GTK 3.x. Thankfully, most of the changes are not hard to adapt to and there are a number of steps that you can take to prepare your GTK 3.x application for the switch to GTK 4. After that, there’s a number of adjustments that you may have to do when you actually switch your application to build against GTK 4.

## Preparation in GTK 3.x

The steps outlined in the following sections assume that your application is working with GTK 3.24, which is the final stable release of GTK 3.x. It includes all the necessary APIs and tools to help you port your application to GTK 4. If you are using an older version of GTK 3.x, you should first get your application to build and work with the latest minor release in the 3.24 series.

### Do not use deprecated symbols

Over the years, a number of functions, and in some cases, entire widgets have been deprecated. These deprecations are clearly spelled out in the API reference, with hints about the recommended replacements. The API reference for GTK 3 also includes an index of all deprecated symbols.

To verify that your program does not use any deprecated symbols, you can use defines to remove deprecated symbols from the header files, as follows:

    make CFLAGS+="-DGDK_DISABLE_DEPRECATED -DGTK_DISABLE_DEPRECATED"

Note that some parts of our API, such as enumeration values, are not well covered by the deprecation warnings. In most cases, using them will require you to also use deprecated functions, which will trigger warnings.

### Enable diagnostic warnings

Deprecations of properties and signals cannot be caught at compile time, as both properties and signals are installed and used after types have been instantiated. In order to catch deprecations and changes in the run time components, you should use the `G_ENABLE_DIAGNOSTIC` environment variable when running your application, e.g.:

    G_ENABLE_DIAGNOSTIC=1 ./your-app

### Do not use GTK-specific command line arguments

GTK 4 does not parse command line arguments any more. If you are using command line arguments like `--gtk-debug` you should use the `GTK_DEBUG` environment variable instead. If you are using `--g-fatal-warnings` for debugging purposes, you should use the `G_DEBUG` environment variable, as specified by the GLib documentation.

### Do not use widget style properties

Style properties do not exist in GTK 4. You should stop using them in your custom CSS and in your code.

### Review your window creation flags

GTK 4 removes the `GDK_WA_CURSOR` flag. Instead, just use `gdk_window_set_cursor()` to set a cursor on the window after creating it. GTK 4 also removes the `GDK_WA_VISUAL` flag, and always uses an RGBA visual for windows. To prepare your code for this, use `gdk_window_set_visual (gdk_screen_get_rgba_visual ())` after creating your window. GTK 4 also removes the `GDK_WA_WMCLASS` flag. If you need this X11-specific functionality, use `XSetClassHint()` directly.

### Stop using direct access to GdkEvent structs

In GTK 4, event structs are opaque and immutable. Many fields already have accessors in GTK 3, and you should use those to reduce the amount of porting work you have to do at the time of the switch.

### Stop using `gdk_pointer_warp()`

Warping the pointer is disorienting and unfriendly to users. GTK 4 does not support it. In special circumstances (such as when implementing remote connection UIs) it can be necessary to warp the pointer; in this case, use platform APIs such as `XWarpPointer()` directly.

### Stop using non-RGBA visuals

GTK 4 always uses RGBA visuals for its windows; you should make sure that your code works with such visuals. At the same time, you should stop using `GdkVisual` APIs, since this object not longer exists in GTK 4. Most of its APIs are deprecated already and not useful when dealing with RGBA visuals.

### Stop using `gtk_widget_set_app_paintable`

This is gone in GTK4 with no direct replacement. But for some usecases there are alternatives. If you want to make the background transparent, you can set the background color to, for example, `rgba(255, 255, 255, 0)` using CSS instead.

### Stop using `GtkBox` padding, fill and expand child properties

GTK 4 removes these `GtkBox` child properties, so you should stop using them. You can replace `GtkBox:padding` using `GtkWidget`‘s `margin-*` properties on your child widgets.

The fill child property can be replaced by setting appropriate values for the `GtkWidget:halign` and `GtkWidget:valign` properties of the child widgets. If you previously set the `fill` child property to `TRUE`, you can achieve the same effect by setting the `halign` or `valign` properties to `GTK_ALIGN_FILL`, depending on the parent box — `halign` for a horizontal box, `valign` for a vertical one.

`GtkBox` also uses the expand child property. It can be replaced by setting `GtkWidget:hexpand` or `GtkWidget:vexpand` on the child widgets. To match the old behavior of the `GtkBox`‘s expand child property, you need to set `hexpand` on the child widgets of a horizontal `GtkBox` and `vexpand` on the child widgets of a vertical `GtkBox`.

Note that there’s a subtle but important difference between `GtkBox`‘s `expand` and `fill` child properties and the ones in `GtkWidget`: setting `GtkWidget:hexpand` or `GtkWidget:vexpand` to `TRUE` will propagate up the widget hierarchy, so a pixel-perfect port might require you to reset the expansion flags to `FALSE` in a parent widget higher up the hierarchy.

### Stop using the state argument of `GtkStyleContext` getters

The getters in the `GtkStyleContext` API, such as `gtk_style_context_get_property()`, `gtk_style_context_get()`, or `gtk_style_context_get_color()` only accept the context’s current state for their state argument. You should update all callers to pass the current state.

### Stop using `gdk_pixbuf_get_from_window()` and `gdk_cairo_set_source_window()`

These functions are not supported in GTK 4. Instead, either use backend-specific APIs, or render your widgets using `Gtk.WidgetClass.snapshot`, once you are using GTK 4.

### Stop using `GtkButton`'s image-related API

The functions and properties related to automatically add a `GtkImage` to a `GtkButton`, and using a `GtkSetting` to control its visibility, are not supported in GTK 4. Instead, you can just pack a GtkImage inside a GtkButton, and control its visibility like you would for any other widget. If you only want to add a named icon to a GtkButton, you can use `gtk_button_new_from_icon_name()`.

### Stop using `GtkWidget` event signals

Event controllers and gestures replace event signals in GTK 4.

Most of them have been backported to GTK 3.x so you can prepare for this change.

Signal | Event controller
--- | ---
::event | `GtkEventControllerLegacy`
::event-after | `GtkEventControllerLegacy`
::button-press-event | `GtkGestureClick`
::button-release-event | `GtkGestureClick`
::touch-event | various touch gestures
::scroll-event | `GtkEventControllerScroll`
::motion-notify-event | `GtkEventControllerMotion`
::delete-event | -
::key-press-event | `GtkEventControllerKey`
::key-release-event | `GtkEventControllerKey`
::enter-notify-event | `GtkEventControllerMotion`
::leave-notify-event | `GtkEventControllerMotion`
::configure-event | -
::focus-in-event | `GtkEventControllerFocus`
::focus-out-event | `GtkEventControllerFocus`
::map-event | -
::unmap-event | -
::property-notify-event | replaced by `GdkClipboard`
::selection-clear-event | replaced by `GdkClipboard`
::selection-request-event | replaced by `GdkClipboard`
::selection-notify-event | replaced by `GdkClipboard`
Drag-and-Drop signals | `GtkDragSource`, `GtkDropTarget`
::proximity-in-event | `GtkGestureStylus`
::proximity-out-event | `GtkGestureStylus`
::visibility-notify-event | -
::window-state-event | -
::damage-event | -
::grab-broken-event | -

Event signals which are not directly related to input have to be dealt with on a one-by-one basis:

- If you were using `::configure-event` and `::window-state-event` to save window state, you should use property notification for corresponding `GtkWindow` properties, such as `GtkWindow:default-width`, `GtkWindow:default-height`, `GtkWindow:maximized` or `GtkWindow:fullscreened`.
- If you were using `::delete-event` to present a confirmation when using the close button of a window, you should use the `GtkWindow::close-request` signal.
- If you were using `::map-event` and `::unmap-event` to track a window being mapped, you should use property notification for the `GdkSurface:mapped` property instead.
- The `::damage-event` signal has no replacement, as the only consumer of damage events were the offscreen GDK surfaces, which have no replacement in GTK 4.x.

### Set a proper application ID

In GTK 4 we want the application’s `GApplication` ‘application-id’ (and therefore the D-Bus name), the desktop file basename and Wayland’s xdg-shell `app_id` to match. In order to achieve this with GTK 3.x call `g_set_prgname()` with the same application ID you passed to `GtkApplication`. Rename your desktop files to match the application ID if needed.

The call to `g_set_prgname()` can be removed once you fully migrated to GTK 4.

You should be aware that changing the application ID makes your application appear as a new, different app to application installers. You should consult the appstream documentation for best practices around renaming applications.

### Stop using `gtk_main()` and related APIs

GTK 4 removes the `gtk_main_*` family of APIs. The recommended replacement is `GtkApplication`, but you can also iterate the GLib main loop directly, using `GMainContext` APIs. The replacement for `gtk_events_pending()` is `g_main_context_pending()`, the replacement for `gtk_main_iteration()` is `g_main_context_iteration()`.

In GTK 4, you can use this replacement that will iterate the default main loop until all windows have been closed:

    while (g_list_model_get_n_items (gtk_window_get_toplevels ()) > 0)
      g_main_context_iteration (NULL, TRUE);

### Reduce the use of `gtk_widget_destroy()`

GTK 4 introduces a `gtk_window_destroy()` api. While that is not available in GTK 3, you can prepare for the switch by using `gtk_widget_destroy()` only on toplevel windows, and replace all other uses with `gtk_container_remove()` or `g_object_unref()`.

### Stop using the GtkWidget.destroy vfunc

Instead of implementing GtkWidget.destroy, you can implement GObject.dispose.

### Reduce the use of generic container APIs

GTK 4 removes `gtk_container_add()` and `gtk_container_remove()`. While there is not always a replacement for `gtk_container_remove()` in GTK 3, you can replace many uses of `gtk_container_add()` with equivalent container-specific APIs such as `gtk_grid_attach()`, and thereby reduce the amount of work you have to do at the time of the switch.

### Review your use of icon resources

When using icons as resources, the behavior of GTK 4 is different in one respect: Icons that are directly in `$APP_ID/icons/` are treated as unthemed icons, which also means that symbolic icons are not recolored. If you want your icon resources to have icon theme semantics, they need to be placed into theme subdirectories such as `$APP_ID/icons/16x16/actions` or `$APP_ID/icons/scalable/status`.

This location works fine in GTK 3 too, so you can prepare for this change before switching to GTK 4.

## Changes that need to be done at the time of the switch

This section outlines porting tasks that you need to tackle when you get to the point that you actually build your application against GTK 4. Making it possible to prepare for these in GTK 3 would have been either impossible or impractical.

### Larger changes

Some of the larger themes of GTK 4 development are hard to cover in the form of checklist items, so we mention them separately up-front.

#### Subclassing

Compared to previous versions, GTK 4 emphasizes composition and delegation over subclassing. As a consequence, many widgets can no longer be subclassed. In most cases, you should look deriving your widget directly from GtkWidget and use complex widgets as child widgets instead of deriving from them.

#### Life-cycle handling

Widgets in GTK 4 are treated like any other objects - their parent widget holds a reference on them, and GTK holds a reference on toplevel windows. `gtk_window_destroy()` will drop the reference on the toplevel window, and cause the whole widget hierarchy to be finalized unless there are other references that keep widgets alive.

The `GtkWidget::destroy` signal is emitted when a widget is disposed, and therefore can no longer be used to break reference cycles. A typical sign of a reference cycle involving a toplevel window is when closing the window does not make the application quit.

### Stop using GdkScreen

The `GdkScreen` object has been removed in GTK 4. Most of its APIs already had replacements in GTK 3 and were deprecated, a few remaining replacements have been added to `GdkDisplay`.

### Stop using the root window

The root window is an X11-centric concept that is no longer exposed in the backend-neutral GDK API. If you need to interact with the X11 root window, you can use GdkX11.Display.get_xrootwindow to get its XID.

### Stop using `GdkVisual`

This object is not useful with current GTK drawing APIs and has been removed without replacement.

### Stop using `GdkDeviceManager`

The `GdkDeviceManager` object has been removed in GTK 4. Most of its APIs already had replacements in GTK 3 and were deprecated in favor of `GdkSeat`.

### Adapt to `GdkWindow` API changes

`GdkWindow` has been renamed to `GdkSurface`.

In GTK 4, the two roles of a standalone toplevel window and of a popup that is placed relative to a parent window have been separated out into two interfaces, `GdkToplevel` and `GdkPopup`. Surfaces implementing these interfaces are created with `gdk_surface_new_toplevel()` and `gdk_surface_new_popup()`, respectively, and they are presented on screen using `gdk_toplevel_present()` and `gdk_popup_present()`. The `present()` functions take parameters in the form of an auxiliary layout struct, `GdkPopupLayout` or `GdkToplevelLayout`.

If your code is dealing directly with surfaces, you may have to change it to call the API in these interfaces, depending on whether the surface you are dealing with is a toplevel or a popup.

As part of this reorganization, X11-only concepts such as sticky, keep-below, urgency, skip-taskbar or window groups have either been removed or moved to X11 backend api. If you need to use them on your X11 windows, you will have to use those backend apis or set the corresponding X11 properties (as specified in the EWMH) yourself.

Subsurfaces are not currently supported. Native and foreign subwindows are no longer supported. These concepts were complicating the code and could not be supported across backends.

A number of GdkWindow APIs are no longer available. This includes `gdk_window_reparent()`, `gdk_window_set_geometry_hints()`, `gdk_window_raise()`, `gdk_window_restack()`, `gdk_window_move()`, `gdk_window_resize()`. If you need to manually control the position or stacking of your X11 windows, you you will have to use Xlib apis.

A number of minor API cleanups have happened in `GdkSurface` as well. For example, `gdk_surface_input_shape_combine_region()` has been renamed to `gdk_surface_set_input_region()`, and `gdk_surface_begin_resize_drag()` has been renamed to `gdk_toplevel_begin_resize()`.

### The "iconified" window state has been renamed to "minimized"

The `GDK_TOPLEVEL_STATE_ICONIFIED` value of the `GdkSurfaceState` enumeration is now `GDK_TOPLEVEL_STATE_MINIMIZED` in the `GdkToplevelState` enumeration.

The `GdkWindow` functions `gdk_window_iconify()` and `gdk_window_deiconify()` have been renamed to `gdk_toplevel_minimize()` and `gdk_toplevel_present()`, respectively.

The behavior of the minimization and unminimization operations have not been changed, and they still require support from the underlying windowing system.

### Adapt to `GdkEvent` API changes

Direct access to `GdkEvent` structs is no longer possible in GTK 4. `GdkEvent` is now a strictly read-only type, and you can no longer change any of its fields, or construct new events. All event fields have accessors that you will have to use.

Event compression is always enabled in GTK 4, for both motion and scroll events. If you need to see the uncoalesced motion or scroll history, use `gdk_event_get_history()` on the latest event.

### Stop using grabs

GTK 4 no longer provides the `gdk_device_grab()` or `gdk_seat_grab()` apis. If you need to dismiss a popup when the user clicks outside (the most common use for grabs), you can use the `GdkPopup` `GdkPopup:autohide` property instead. `GtkPopover` also has a `GtkPopover:autohide` property for this. If you need to prevent the user from interacting with a window while a dialog is open, use the `GtkWindow:modal` property of the dialog.

### Adapt to coordinate API changes

A number of coordinate APIs in GTK 3 had variants taking `int` arguments: `gdk_device_get_surface_at_position()`, `gdk_surface_get_device_position()`. These have been changed to use `double` arguments, and the `int` variants have been removed. Update your code accordingly.

Any APIs that deal with global (or root) coordinates have been removed in GTK 4, since not all backends support them. You should replace your use of such APIs with surface-relative equivalents. Examples of such removed APIs are `gdk_window_get_origin()`, `gdk_window_move()` or `gdk_event_get_root_coords()`.

### Adapt to `GdkKeymap` API changes

`GdkKeymap` no longer exists as an independent object.

If you need access to keymap state, it is now exposed as properties on the `GdkDevice` representing the keyboard: `GdkDevice:direction`, `GdkDevice:has-bidi-layouts`, `GdkDevice:caps-lock-state`, `GdkDevice:num-lock-state`, `GdkDevice:scroll-lock-state` and `GdkDevice:modifier-state`. To obtain the keyboard device, you can use

    gdk_seat_get_keyboard (gdk_display_get_default_seat (display)

If you need access to translated keys for event handling, `GdkEvent` now includes all of the translated key state, including consumed modifiers, group and shift level, so there should be no need to manually call `gdk_keymap_translate_keyboard_state()` (which has been removed).

If you need to do forward or backward mapping between key codes and key values, use `gdk_display_map_keycode()` and `gdk_display_map_keyval()`, which are the replacements for `gdk_keymap_get_entries_for_keycode()` and `gdk_keymap_get_entries_for_keyval()`.

### Adapt to changes in keyboard modifier handling

GTK 3 has the idea that use of modifiers may differ between different platforms, and has a `GdkModifierIntent` api to let platforms provide hint about how modifiers are expected to be used. It also promoted the use of `<Primary>` instead of `<Control>` to specify accelerators that adapt to platform conventions.

In GTK 4, the meaning of modifiers has been fixed, and applications are expected to map the platform conventions to the existing modifiers. The expected use of modifiers in GTK 4 is:

`GDK_CONTROL_MASK` (`GDK_META_MASK` on macOS)
  Primary accelerators
`GDK_ALT_MASK`
  Mnemonics
`GDK_SHIFT_MASK`
  Extending selections
`GDK_CONTROL_MASK` (`GDK_META_MASK` on macOS)
  Modifying selections
`GDK_CONTROL_MASK|GDK_ALT_MASK`
  Prevent text input

Consequently, `GdkModifierIntent` and related APIs have been removed, and `<Control>` is preferred over `<Primary>` in accelerators.

In GTK 3 on macOS, the `<Primary>` modifier mapped to the `Command` key. In GTK 4, this is no longer the case: `<Primary>` is synonymous to `<Control>`. If you want to make your application to feel native on macOS, you need to add accelerators for macOS that use the `<Meta>` modifier.

A related change is that GTK 4 no longer supports the use of archaic X11 ‘real’ modifiers with the names Mod1,…, Mod5, and `GDK_MOD1_MASK` has been renamed to `GDK_ALT_MASK` and `GDK_MOD2_MASK` has been renamed to `GDK_META_MASK`.

### Replace `GtkClipboard` with `GdkClipboard`

The `GtkClipboard` API has been removed, and replaced by `GdkClipboard`. There is not direct 1:1 mapping between the old an the new API, so it cannot be a mechanical replacement; the new API is based on object types and `GValue` like object properties, instead of opaque identifiers, so it should be easier to use.

For instance, the example below copies the contents of an entry into the clipboard:

    static void
    copy_text (GtkWidget *widget)
    {
      GtkEditable *editable = GTK_EDITABLE (widget);

      // Initialize a GValue with the contents of the widget
      GValue value = G_VALUE_INIT;
      g_value_init (&value, G_TYPE_STRING);
      g_value_set_string (&value, gtk_editable_get_text (editable));

      // Store the value in the clipboard object
      GdkClipboard *clipboard = gtk_widget_get_clipboard (widget);
      gdk_clipboard_set_value (clipboard, &value);

      g_value_unset (&value);
    }

whereas the example below pastes the contents into the entry:

    static void
    paste_text (GtkWidget *widget)
    {
      GtkEditable *editable = GTK_EDITABLE (widget);

      // Initialize a GValue to receive text
      GValue value = G_VALUE_INIT;
      g_value_init (&value, G_TYPE_STRING);

      // Get the content provider for the clipboard, and ask it for text
      GdkClipboard *clipboard = gtk_widget_get_clipboard (widget);
      GdkContentProvider *provider = gdk_clipboard_get_content (clipboard);

      // If the content provider does not contain text, we are not interested
      if (!gdk_content_provider_get_value (provider, &value, NULL))
        return;

      const char *str = g_value_get_string (&value);

      gtk_editable_set_text (editable, str);

      g_value_unset (&value);
    }

The convenience API for specific target types in `GtkClipboard` has been replaced by their corresponding GType:

GtkClipboard | GType
--- | ---
`gtk_clipboard_request_text()` | `G_TYPE_STRING`
`gtk_clipboard_request_rich_text()` | `GTK_TYPE_TEXT_BUFFER`
`gtk_clipboard_request_image()` | `GDK_TYPE_PIXBUF`
`gtk_clipboard_request_uris()` | `GDK_TYPE_FILE_LIST`

Note: Support for rich text serialization across different processes for `GtkTextBuffer` is not available any more.

If you are copying the contents of an image, it is recommended to use `GDK_TYPE_PAINTABLE` instead of `GDK_TYPE_PIXBUF`, to minimize the amount of potential copies.

### Stop using `gtk_get_current_...` APIs

The function `gtk_get_current_event()` and its variants have been replaced by equivalent event controller APIs: `gtk_event_controller_get_current_event()`, etc.

### Convert your UI files

A number of the changes outlined below affect `.ui` files. The `gtk4-builder-tool simplify` command can perform many of the necessary changes automatically, when called with the `--3to4` option. You should always review the resulting changes.

The `<requires>` tag now supports for the `lib` attribute the `gtk` value only, instead of the `gtk+` one previously.

### Adapt to GtkBuilder API changes

`gtk_builder_connect_signals()` no longer exists. Instead, signals are always connected automatically. If you need to add user data to your signals, `gtk_builder_set_current_object()` must be called. An important caveat is that you have to do this before loading any XML. This means if you need to use `gtk_builder_set_current_object()`, you can no longer use `gtk_builder_new_from_file()`, `gtk_builder_new_from_resource()`, or `gtk_builder_new_from_string()`. Instead, you must use vanilla `gtk_builder_new()`, then call `gtk_builder_set_current_object()`, then load the XML using `gtk_builder_add_from_file()`, `gtk_builder_add_from_resource()`, or `gtk_builder_add_from_string()`. You must check the return value for failure and manually abort with `g_error()` if something went wrong.

You only have to worry about this if you were previously using `gtk_builder_connect_signals()`. If you are using templates, then `gtk_widget_init_template()` will call `gtk_builder_set_current_object()` for you, so templates work like before.

### Adapt to event controller API changes

A few changes to the event controller and `GtkGesture` APIs did not make it back to GTK 3, and have to be taken into account when moving to GTK 4. One is that the `GtkEventControllerMotion::enter` and `GtkEventControllerMotion::leave` signals have gained new arguments. Another is that `GtkGestureMultiPress` has been renamed to `GtkGestureClick`, and has lost its area property. A `GtkEventControllerFocus` has been split off from `GtkEventControllerKey`.

In GTK 3, `GtkEventController:widget` was a construct-only property, so a `GtkWidget` was provided whenever constructing a `GtkEventController`. In GTK 4, `GtkEventController:widget` is now read-only. Use `gtk_widget_add_controller()` to add an event controller to a widget.

In GTK 3, widgets did not own their event controllers, and event controllers did not own their widgets, so developers were responsible for manually keeping event controllers alive for the lifetime of their associated widgets. In GTK 4, widgets own their event controllers. `gtk_widget_add_controller()` takes ownership of the event controller, so there is no longer any need to store a reference to the event controller after it has been added to a widget.

Although not normally needed, an event controller could be removed from a widget in GTK 3 by destroying the event controller with `g_object_unref()`. In GTK 4, you must use `gtk_widget_remove_controller()`.

### Focus handling changes

The semantics of the `GtkWidget:can-focus` property have changed. In GTK 3, this property only meant that the widget itself would not accept keyboard input, but its children still might (in the case of containers). In GTK 4, if `:can-focus` is `FALSE`, the focus cannot enter the widget or any of its descendents, and the default value has changed from `FALSE` to `TRUE`. In addition, there is a `GtkWidget:focusable` property, which controls whether an individual widget can receive the input focus.

The `gtk4-builder-tool` utility, when called with the `--3to4` option of the `simplify` command, will replace `:can-focus` by `:focusable`.

The feature to automatically keep the focus widget scrolled into view with `gtk_container_set_focus_vadjustment()` has been removed together with `GtkContainer`, and is provided by scrollable widgets instead. In the common case that the scrollable is a `GtkViewport`, use `GtkViewport:scroll-to-focus`.

### Use the new apis for keyboard shortcuts

The APIs for keyboard shortcuts and accelerators have changed in GTK 4.

Instead of `GtkAccelGroup`, you now use a `GtkShortcutController` with global scope, and instead of `GtkBindingSet`, you now use `gtk_widget_class_add_shortcut()`, `gtk_widget_class_add_binding()` and its variants. In both cases, you probably want to add actions that can be triggered by your shortcuts.

There is no direct replacement for loading and saving accelerators with `GtkAccelMap`. But since `GtkShortcutController` implements `GListModel` and both `GtkShortcutTrigger` and `GtkShortcutAction` can be serialized to strings, it is relatively easy to implement saving and loading yourself.

### Stop using `GtkEventBox`

`GtkEventBox` is no longer needed and has been removed.

All widgets receive all events.

### Stop using `GtkButtonBox`

`GtkButtonBox` has been removed. Use a `GtkBox` instead.

### Adapt to `GtkBox` API changes

The GtkBox `pack_start()` and `pack_end()` methods have been replaced by `gtk_box_prepend()` and `gtk_box_append()`. You can also reorder box children as necessary.

### Adapt to `GtkWindow` API changes

Following the `GdkSurface` changes, a number of `GtkWindow` APIs that were X11-specific have been removed. This includes `gtk_window_set_position()`, `gtk_window_set_geometry_hints()`, `gtk_window_set_gravity()`, `gtk_window_move()`, `gtk_window_parse_geometry()`, `gtk_window_set_keep_above()`, `gtk_window_set_keep_below()`, `gtk_window_begin_resize_drag()`, `gtk_window_begin_move_drag()`. Most likely, you should just stop using them. In some cases, you can fall back to using the underlying `GdkToplevel` APIs (for example, `gdk_toplevel_begin_resize()`); alternatively, you will need to get the native windowing system surface from the `GtkWindow` and call platform specific API.

The APIs for controlling `GtkWindow` size have changed to be better aligned with the way size changes are integrated in the frame cycle. `gtk_window_resize()` and `gtk_window_get_size()` have been removed. Instead, use `gtk_window_set_default_size()` and `gtk_window_get_default_size()`.

### Adapt to `GtkHeaderBar` and `GtkActionBar` API changes

The `gtk_header_bar_set_show_close_button()` function has been renamed to the more accurate name `gtk_header_bar_set_show_title_buttons()`. The corresponding getter and the property itself have also been renamed. The default value of the property is now `TRUE` instead of `FALSE`.

The `gtk_header_bar_set_custom_title()` function has been renamed to the more accurate name `gtk_header_bar_set_title_widget()`. The corresponding getter and the property itself have also been renamed.

The `gtk_header_bar_set_title()` function has been removed along with its corresponding getter and the property. By default `GtkHeaderBar` shows the title of the window, so if you were setting the title of the header bar, consider setting the window title instead. If you need to show a title that’s different from the window title, use the `GtkHeaderBar:title-widget` property to add a `GtkLabel` as shown in the example in the `GtkHeaderBar` documentation.

The `gtk_header_bar_set_subtitle()` function has been removed along with its corresponding getter and the property. The old “subtitle” behavior can be replicated by setting the `GtkHeaderBar:title-widget` property to a `GtkBox` with two labels inside, with the title label matching the example in `GtkHeaderBar` documentation, and the subtitle label being similar, but with `"subtitle"` style class instead of `"title"`.

The `gtk_header_bar_set_has_subtitle()` function has been removed along with its corresponding getter and the property. Its behavior can be replicated by setting the `GtkHeaderBar:title-widget` property to a `GtkStack` with `GtkStack:vhomogeneous` property set to `TRUE` and two pages, each with a `GtkBox` with title and subtitle as described above.

Some of the internal structure of `GtkHeaderBar` has been made available as public API: `GtkWindowHandle` and `GtkWindowControls`. If you have unusual needs for custom headerbars, these might be useful to you.

The `:pack-type` child properties of `GtkHeaderBar` and `GtkActionBar` have been removed. If you need to programmatically place children, use the `gtk_header_bar_pack_start()` and `gtk_header_bar_pack_end()` methods. In UI files, use the `type` attribute on the `child` element.

The `gtk4-builder-tool` utility can help with this conversion, with the `--3to4` option of the `simplify` command.

### Adapt to GtkStack, GtkAssistant and GtkNotebook API changes

The child properties of `GtkStack`, `GtkAssistant` and `GtkNotebook` have been converted into child meta objects.

Instead of `gtk_container_child_set (stack, child, …)`, you can now use `g_object_set (gtk_stack_get_page (stack, child), …)`. In .ui files, the `GtkStackPage` objects must be created explicitly, and take the child widget as property. The changes to `GtkNotebook` and `GtkAssistant` are similar.

`gtk4-builder-tool` can help with this conversion, with the `--3to4` option of the `simplify` command.

### Adapt to button class hierarchy changes

`GtkCheckButton` is no longer derived from `GtkToggleButton`. Call `gtk_check_button_set_active()` instead of `gtk_toggle_button_set_active()`.

`GtkRadioButton` has been removed, and its grouping functionality has been added to `GtkCheckButton` and `GtkToggleButton`. Use grouped check buttons for traditional radio groups, and used grouped toggle buttons for view switchers. The new API to set up groups of buttons is `gtk_check_button_set_group()` and `gtk_toggle_button_set_group()`.

`gtk4-builder-tool` can help with this conversion, with the `--3to4` option of the `simplify` command.

### Adapt to GtkScrolledWindow API changes

The constructor for `GtkScrolledWindow` no longer takes the adjustments as arguments - these were almost always `NULL`.

### Adapt to GtkBin removal

The abstract base class `GtkBin` for single-child containers has been removed. The former subclasses are now derived directly from `GtkWidget`, and have a “child” property for their child widget. To add a child, use the setter for the “child” property (e.g. `gtk_frame_set_child()`) instead of `gtk_container_add()`. Adding a child in a ui file with `<child>` still works.

The affected classes are:

- `GtkAspectFrame`
- `GtkButton` (and subclasses)
- `GtkComboBox`
- `GtkFlowBoxChild`
- `GtkFrame`
- `GtkListBoxRow`
- `GtkOverlay`
- `GtkPopover`
- `GtkRevealer`
- `GtkScrolledWindow`
- `GtkSearchBar`
- `GtkViewport`
- `GtkWindow` (and subclasses)

If you have custom widgets that were derived from `GtkBin`, you should port them to derive from `GtkWidget`. Notable vfuncs that you will have to implement include the `GObject` dispose vfunc (to unparent your child), `Gtk.WidgetClass.compute_expand` (if you want your container to propagate expand flags) and `Gtk.WidgetClass.get_request_mode` (if you want your container to support height-for-width).

You may also want to implement the `GtkBuildable` interface, to support adding children with `<child>` in ui files.

### Adapt to GtkContainer removal

The abstract base class `GtkContainer` for general containers has been removed. The former subclasses are now derived directly from `GtkWidget`, and have class-specific `add()` and `remove()` functions.

The most noticeable change is the use of `gtk_box_append()` or `gtk_box_prepend()` instead of `gtk_container_add()` for adding children to `GtkBox`, and the change to use container-specific remove functions, such as `gtk_stack_remove()` instead of `gtk_container_remove()`. Adding a child in a ui file with `<child>` still works.

The affected classes are:

- `GtkActionBar`
- `GtkBox` (and subclasses)
- `GtkExpander`
- `GtkFixed`
- `GtkFlowBox`
- `GtkGrid`
- `GtkHeaderBar`
- `GtkIconView`
- `GtkInfoBar`
- `GtkListBox`
- `GtkNotebook`
- `GtkPaned`
- `GtkStack`
- `GtkTextView`
- `GtkTreeView`

Without `GtkContainer`, there are no longer facilities for defining and using child properties. If you have custom widgets using child properties, they will have to be converted either to layout properties provided by a layout manager (if they are layout-related), or handled in some other way. One possibility is to use child meta objects, as seen with `GtkAssistantPage`, `GtkStackPage` and the like.

If you used to define child properties with `<packing>` in ui files, you have to switch to using `<layout>` for the corresponding layout properties. `gtk4-builder-tool` can help with this conversion, with the `--3to4` option of the `simplify` command.

The replacements for `gtk_container_add()` are:

Widget | Replacement
--- | ---
`GtkActionBar` | `gtk_action_bar_pack_start()`, `gtk_action_bar_pack_end()`
`GtkBox` | `gtk_box_prepend()`, `gtk_box_append()`
`GtkExpander` | `gtk_expander_set_child()`
`GtkFixed` | `gtk_fixed_put()`
`GtkFlowBox` | `gtk_flow_box_insert()`
`GtkGrid` | `gtk_grid_attach()`
`GtkHeaderBar` | `gtk_header_bar_pack_start()`, `gtk_header_bar_pack_end()`
`GtkIconView` | -
`GtkInfoBar` | `gtk_info_bar_add_child()`
`GtkListBox` | `gtk_list_box_insert()`
`GtkNotebook` | `gtk_notebook_append_page()`
`GtkPaned` | `gtk_paned_set_start_child()`, `gtk_paned_set_end_child()`
`GtkStack` | `gtk_stack_add_child()`
`GtkTextView` | `gtk_text_view_add_child_at_anchor()`, `gtk_text_view_add_overlay()`
`GtkTreeView` | -

### Stop using GtkContainer::border-width

GTK 4 has removed the `GtkContainer::border-width` property (together with the rest of `GtkContainer`). Use other means to influence the spacing of your containers, such as the CSS margin and padding properties on child widgets, or the CSS border-spacing property on containers.

### Adapt to `gtk_widget_destroy()` removal

The function `gtk_widget_destroy()` has been removed. To explicitly destroy a toplevel window, use `gtk_window_destroy()`. To destroy a widget that is part of a hierarchy, remove it from its parent using a container-specific remove API, such as `gtk_box_remove()` or `gtk_stack_remove()`. To destroy a freestanding non-toplevel widget, use `g_object_unref()` to drop your reference.

### Adapt to coordinate API changes

A number of APIs that are accepting or returning coordinates have been changed from `int`s to `double`s: `gtk_widget_translate_coordinates()`, `gtk_fixed_put()`, `gtk_fixed_move()`. This change is mostly transparent, except for cases where out parameters are involved: you need to pass `double*` now, instead of `int*`.

### Adapt to GtkStyleContext API changes

The getters in the GtkStyleContext API, such as `gtk_style_context_get_color()`, `gtk_style_context_get_border()`, or `gtk_style_context_get_margin()` have lost their state argument, and always use the context’s current state. Update all callers to omit the state argument.

The most commonly used GtkStyleContext API, `gtk_style_context_add_class()`, has been moved to GtkWidget as `gtk_widget_add_css_class()`, as have the corresponding `gtk_style_context_remove_class()` and `gtk_style_context_has_class()` APIs.

### Adapt to GtkCssProvider API changes

In GTK 4, the various `GtkCssProvider` load functions have lost their `GError` argument. If you want to handle CSS loading errors, use the `GtkCssProvider::parsing-error` signal instead. `gtk_css_provider_get_named()` has been replaced by `gtk_css_provider_load_named()`.

### Stop using GtkShadowType and GtkRelief properties

The shadow-type properties in `GtkScrolledWindow`, `GtkViewport`, and `GtkFrame`, as well as the relief properties in `GtkButton` and its subclasses have been removed. `GtkScrolledWindow`, `GtkButton` and `GtkMenuButton` have instead gained a boolean has-frame property.

### Adapt to GtkWidget's size request changes

GTK 3 used five different virtual functions in GtkWidget to implement size requisition, namely the `gtk_widget_get_preferred_width()` family of functions. To simplify widget implementations, GTK 4 uses only one virtual function, `Gtk.WidgetClass.measure`, that widgets have to implement. `gtk_widget_measure()` replaces the various `gtk_widget_get_preferred_` functions for querying sizes.

### Adapt to GtkWidget's size allocation changes

The `Gtk.WidgetClass.size_allocate` vfunc takes the baseline as an argument now, so you no longer need to call `gtk_widget_get_allocated_baseline()` to get it.

The ::size-allocate signal has been removed, since it is easy to misuse. If you need to learn about sizing changes of custom drawing widgets, use the `GtkDrawingArea::resize` or `GtkGLArea::resize` signals. If you want to track the size of toplevel windows, use property notification for `GtkWindow:default-width` and `GtkWindow:default-height`.

### Switch to GtkWidget's children APIs

In GTK 4, any widget can have children (and `GtkContainer` is gone). There is new API to navigate the widget tree, for use in widget implementations: `gtk_widget_get_first_child()`, `gtk_widget_get_last_child()`, `gtk_widget_get_next_sibling()`, `gtk_widget_get_prev_sibling()`.

### Don't use -gtk-gradient in your CSS

GTK now supports standard CSS syntax for both linear and radial gradients, just use those.

### Don't use -gtk-icon-effect in your CSS

GTK now supports a more versatile -gtk-icon-filter instead.

Replace

Old | Replacement
--- | ---
-gtk-icon-effect: dim | -gtk-icon-filter: opacity(0.5)
-gtk-icon-effect: highlight | -gtk-icon-filter: brightness(1.2)

### Don't use -gtk-icon-theme in your CSS

GTK 4 always uses the current icon theme, with no way to change this.

### Don't use -gtk-outline-...-radius in your CSS

These non-standard properties have been removed from GTK CSS. Just use regular border radius.

### Adapt to drawing model changes

This area has seen the most radical changes in the transition from GTK 3 to GTK 4. Widgets no longer use a `draw()` function to render their contents to a cairo surface. Instead, they have a `Gtk.WidgetClass.snapshot` function that creates one or more GskRenderNodes to represent their content. Third-party widgets that use a `draw()` function or a `GtkWidget::draw` signal handler for custom drawing will need to be converted to use `gtk_snapshot_append_cairo()`.

The auxiliary `GtkSnapshot` object has APIs to help with creating render nodes.

If you are using a `GtkDrawingArea` for custom drawing, you need to switch to using `gtk_drawing_area_set_draw_func()` to set a draw function instead of connecting a handler to the `GtkWidget::draw` signal.

### Stop using APIs to query GdkSurfaces

A number of APIs for querying special-purpose windows have been removed, since these windows no longer exist: `gtk_tree_view_get_bin_window()`, `gtk_viewport_get_bin_window()`, `gtk_viewport_get_view_window()`.

### Widgets are now visible by default

The default value of `GtkWidget:visible` in GTK 4 is `TRUE`, so you no longer need to explicitly show all your widgets. On the flip side, you need to hide widgets that are not meant to be visible from the start. The only widgets that still need to be explicitly shown are toplevel windows, dialogs and popovers.

A convenient way to remove unnecessary property assignments like this from ui files it run the command `gtk4-builder-tool simplify --replace` on them.

The function `gtk_widget_show_all()`, the `GtkWidget:no-show-all` property and its getter and setter have been removed in GTK 4, so you should stop using them.

### Adapt to changes in animated hiding and showing of widgets

Widgets that appear and disappear with an animation, such as `GtkInfoBar`, `GtkRevealer` no longer use `gtk_widget_show()` and `gtk_widget_hide()` for this, but have gained dedicated APIs for this purpose that you should use instead, such as `gtk_info_bar_set_revealed()`.

### Stop passing commandline arguments to gtk_init

The `gtk_init()` and `gtk_init_check()` functions no longer accept commandline arguments. Just call them without arguments. Other initialization functions that were purely related to commandline argument handling, such as `gtk_parse_args()` and `gtk_get_option_group()`, are gone.

The APIs to initialize GDK separately are also gone, but it is very unlikely that you are affected by that.

### GdkPixbuf is deemphasized

A number of `GdkPixbuf`-based APIs have been removed. The available replacements are either using `GIcon`, or the newly introduced `GdkTexture` or `GdkPaintable` classes instead. If you are dealing with pixbufs, you can use `gdk_texture_new_for_pixbuf()` to convert them to texture objects where needed.

### GtkWidget event signals are removed

Event controllers and GtkGestures have already been introduced in GTK 3 to handle input for many cases. In GTK 4, the traditional widget signals for handling input, such as `GtkWidget::motion-event` or `GtkWidget::event` have been removed. All event handling is done via event controllers now.

### Invalidation handling has changed

Only `gtk_widget_queue_draw()` is left to mark a widget as needing redraw. Variations like `gtk_widget_queue_draw_rectangle()` or `gtk_widget_queue_draw_region()` are no longer available.

### Stop using GtkWidget::draw

The `GtkWidget::draw` signal has been removed. Widgets need to implement the `Gtk.WidgetClass.snapshot` function now. Connecting draw signal handlers is no longer possible. If you want to keep using cairo for drawing, use `gtk_snapshot_append_cairo()`.

### Window content observation has changed

Observing widget contents and widget size is now done by using the `GtkWidgetPaintable` object instead of connecting to widget signals.

### Monitor handling has changed

Instead of a monitor number, `GdkMonitor` is now used throughout. `gdk_display_get_monitors()` returns the list of monitors that can be queried or observed for monitors to pass to APIs like `gtk_window_fullscreen_on_monitor()`.

### Adapt to monitor API changes

The `gdk_monitor_get_workarea()` API is gone. Individual backends can still provide this information, for example with GdkX11.Monitor.get_workarea.

If you use this information, your code should check which backend is in use and then call the appropriate backend API.

### Adapt to cursor API changes

Use the new `gtk_widget_set_cursor()` function to set cursors, instead of setting the cursor on the underlying window directly. This is necessary because most widgets don’t have their own window anymore, turning any such calls into global cursor changes.

For creating standard cursors, `gdk_cursor_new_for_display()` has been removed, you have to use cursor names instead of `GdkCursorType`. For creating custom cursors, use `gdk_cursor_new_from_texture()`. The ability to get cursor images has been removed.

### Adapt to icon size API changes

Instead of the existing extensible set of symbolic icon sizes, GTK now only supports normal and large icons with the `GtkIconSize` enumeration. The actual sizes can be defined by themes via the CSS property -gtk-icon-size.

GtkImage setters like `gtk_image_set_from_icon_name()` no longer take a `GtkIconSize` argument. You can use the separate `gtk_image_set_icon_size()` setter if you need to override the icon size.

The :stock-size property of GtkCellRendererPixbuf has been renamed to `GtkCellRendererPixbuf:icon-size`.

### Adapt to changes in the GtkAssistant API

The :has-padding property is gone, and `GtkAssistant` no longer adds padding to pages. You can easily do that yourself.

### Adapt to changes in the API of GtkEntry, GtkSearchEntry and GtkSpinButton

The `GtkEditable` interface has been made more useful, and the core functionality of `GtkEntry` has been broken out as a `GtkText` widget. `GtkEntry`, `GtkSearchEntry`, `GtkSpinButton` and the new `GtkPasswordEntry` now use a `GtkText` widget internally and implement `GtkEditable`. In particular, this means that it is no longer possible to use `GtkEntry` API such as `gtk_entry_grab_focus_without_selecting()` on a search entry.

Use `GtkEditable` API for editable functionality, and widget-specific APIs for things that go beyond the common interface. For password entries, use `GtkPasswordEntry`. As an example, `gtk_spin_button_set_max_width_chars()` has been removed in favor of `gtk_editable_set_max_width_chars()`.

### Adapt to changes in GtkOverlay API

The GtkOverlay :pass-through child property has been replaced by the `GtkWidget:can-target` property. Note that they have the opposite sense: pass-through == !can-target.

### Use GtkFixed instead of GtkLayout

Since `GtkScrolledWindow` can deal with widgets that do not implement the `GtkScrollable` interface by automatically wrapping them into a `GtkViewport`, `GtkLayout` is redundant, and has been removed in favor of the existing `GtkFixed` widget.

### Adapt to search entry changes

The way search entries are connected to global events has changed; `gtk_search_entry_handle_event()` has been dropped and replaced by `gtk_search_entry_set_key_capture_widget()` and `gtk_event_controller_key_forward()`.

### Adapt to GtkScale changes

The default value of `GtkScale:draw-value` has been changed to `FALSE`. If you want your scales to draw values, you will have to set this property explicitly now.

`gtk4-builder-tool` can help with this conversion, with the `--3to4` option of the `simplify` command.

### Stop using `gtk_window_activate_default()`

The handling of default widgets has been changed, and activating the default now works by calling `gtk_widget_activate_default()` on the widget that caused the activation. If you have a custom widget that wants to override the default handling, you can provide an implementation of the “default.activate” action in your widgets’ action groups.

### Stop using `gtk_widget_grab_default()`

The function `gtk_widget_grab_default()` has been removed. If you need to mark a widget as default, use `gtk_window_set_default_widget()` directly.

### Stop setting ::has-default and ::has-focus in .ui files

The special handling for the :has-default and :has-focus properties has been removed. If you want to define the initial focus or the the default widget in a .ui file, set the `GtkWindow:default-widget` or `GtkWindow:focus-widget` properties of the toplevel window.

### Stop using the GtkWidget::display-changed signal

To track the current display, use the `GtkWidget:root` property instead.

### GtkPopover::modal has been renamed to autohide

The modal property has been renamed to `GtkPopover:autohide`.

`gtk-builder-tool` can assist with the rename in ui files.

### gtk_widget_get_surface has been removed

`gtk_widget_get_surface()` has been removed. Use `gtk_native_get_surface()` in combination with `gtk_widget_get_native()` instead.

### gtk_widget_is_toplevel has been removed

`gtk_widget_is_toplevel()` has been removed. Use `GTK_IS_ROOT`, `GTK_IS_NATIVE` or `GTK_IS_WINDOW` instead, as appropriate.

### gtk_widget_get_toplevel has been removed

`gtk_widget_get_toplevel()` has been removed. Use `gtk_widget_get_root()` or `gtk_widget_get_native()` instead, as appropriate.

### GtkEntryBuffer ::deleted-text has changed

To allow signal handlers to access the deleted text before it has been deleted, the `GtkEntryBuffer::deleted-text` signal has changed from `G_SIGNAL_RUN_FIRST` to `G_SIGNAL_RUN_LAST`. The default handler removes the text from the `GtkEntryBuffer`.

To adapt existing code, use `g_signal_connect_after()` or `G_CONNECT_AFTER` when using `g_signal_connect_data()` or `g_signal_connect_object()`.

### GtkMenu, GtkMenuBar and GtkMenuItem are gone

These widgets were heavily relying on X11-centric concepts such as override-redirect windows and grabs, and were hard to adjust to other windowing systems.

Menus can already be replaced using GtkPopoverMenu in GTK 3. Additionally, GTK 4 introduces GtkPopoverMenuBar to replace menubars. These new widgets can only be constructed from menu models, so the porting effort involves switching to menu models and actions.

Tabular menus were rarely used and complicated the menu code, so they have not been brought over to `GtkPopoverMenu`. If you need complex layout in menu-like popups, consider directly using a `GtkPopover` instead.

Since menus are gone, `GtkMenuButton` also lost its ability to show menus, and needs to be used with popovers in GTK 4.

### GtkToolbar has been removed

Toolbars were using outdated concepts such as requiring special toolitem widgets. Toolbars should be replaced by using a `GtkBox` with regular widgets instead and the “toolbar” style class.

### GtkAspectFrame is no longer a frame

`GtkAspectFrame` is no longer derived from `GtkFrame` and does not place a label and frame around its child anymore. It still lets you control the aspect ratio of its child.

### Stop using custom tooltip windows

Tooltips no longer use `GtkWindow`s in GTK 4, and it is no longer possible to provide a custom window for tooltips. Replacing the content of the tooltip with a custom widget is still possible, with `gtk_tooltip_set_custom()`.

### Switch to the new Drag-and-Drop api

The source-side Drag-and-Drop apis in GTK 4 have been changed to use an event controller, `GtkDragSource`. Instead of calling `gtk_drag_source_set()` and connecting to `GtkWidget` signals, you create a `GtkDragSource` object, attach it to the widget with `gtk_widget_add_controller()`, and connect to `GtkDragSource` signals. Instead of calling `gtk_drag_begin()` on a widget to start a drag manually, call `gdk_drag_begin()`. The `::drag-data-get` signal has been replaced by the `GtkDragSource::prepare` signal, which returns a `GdkContentProvider` for the drag operation.

The destination-side Drag-and-Drop API in GTK 4 have also been changed to use an event controller, `GtkDropTarget`. Instead of calling `gtk_drag_dest_set()` and connecting to `GtkWidget` signals, you create a `GtkDropTarget` object, attach it to the widget with `gtk_widget_add_controller()`, and connect to `GtkDropTarget` signals. The `::drag-motion` signal has been renamed to `GtkDropTarget::accept`, and instead of `::drag-data-received`, you need to use async read methods on the `GdkDrop` object, such as `gdk_drop_read_async()` or `gdk_drop_read_value_async()`.

### Adapt to GtkIconTheme API changes

`gtk_icon_theme_lookup_icon()` returns a `GtkIconPaintable` object now, instead of a `GtkIconInfo`. It always returns a paintable in the requested size, and never fails. A number of no-longer-relevant lookup flags and API variants have been removed.

Note that while GTK 4 is moving towards `GdkPaintable` as a primary API for paintable content, it is meant to be a ‘pure’ content producer, therefore a `GtkIconPaintable` for a symbolic icon will not get recolored depending on the context it is rendered it. To properly render a symbolic icon that is provided in the form of a `GtkIconPaintable` (this can be checked with `gtk_icon_paintable_is_symbolic()`), you have to call `gtk_icon_paintable_get_icon_name()` and set the icon name on a `GtkImage`.

### Adapt to GtkImage changes

`GtkPicture`‘s behaviour was “split out” of `GtkImage` as the latter was covering too many use cases; if you’re loading an icon, `GtkImage` in GTK3 and GTK4 are perfectly equivalent. If you are loading a more complex image asset, like a picture or a thumbnail, then `GtkPicture` is the appropriate widget.

One noteworthy distinction is that while `GtkImage` has its size computed by GTK, `GtkPicture` lets you decide about the size.

### Update to GtkFileChooser API changes

`GtkFileChooser` moved to a GFile-based API. If you need to convert a path or a URI, use `g_file_new_for_path()`, `g_file_new_for_commandline_arg()`, or `g_file_new_for_uri()`; similarly, if you need to get a path, name or URI from a `GFile`, use `g_file_get_path()`, `g_file_get_basename()` or `g_file_get_uri()`. With the removal or path and URI-based functions, the “local-only” property has been removed; GFile can be used to access non-local as well as local resources.

The `GTK_FILE_CHOOSER_ACTION_CREATE_FOLDER` action has been removed. Use `GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER`, instead. If a new folder is needed, the user can create one.

The “confirm-overwrite” signal, and the “do-overwrite-confirmation” property have been removed from `GtkFileChooser`. The file chooser widgets will automatically handle the confirmation of overwriting a file when using `GTK_FILE_CHOOSER_ACTION_SAVE`.

`GtkFileChooser` does not support a custom extra widget any more. If you need to add extra widgets, use `gtk_file_chooser_add_choice()` instead.

`GtkFileChooser` does not support a custom preview widget any more.

### Stop using blocking dialog functions

`GtkDialog`, `GtkNativeDialog`, and `GtkPrintOperation` removed their blocking API using nested main loops. Nested main loops present re-entrancy issues and other hard to debug issues when coupled with other event sources (IPC, accessibility, network operations) that are not under the toolkit or the application developer’s control. Additionally, “stop-the-world” functions do not fit the event-driven programming model of GTK.

You can replace calls to `gtk_dialog_run()` by specifying that the `GtkDialog` must be modal using `gtk_window_set_modal()` or the `GTK_DIALOG_MODAL` flag, and connecting to the `GtkDialog::response` signal.

### Stop using GtkBuildable API

All the `GtkBuildable` API was made private, except for the getter function to retrieve the buildable ID. If you are using `gtk_buildable_get_name()` you should replace it with `gtk_buildable_get_buildable_id()`.

### Adapt to GtkAboutDialog API changes

`GtkAboutDialog` now directly derives from `GtkWindow`, the `GtkDialog` API can no longer be used on it.

### Adapt to GtkTreeView and GtkIconView tooltip context changes

The getter functions for retrieving the data from `GtkTreeView` and `GtkIconView` inside a `GtkWidget::query-tooltip` signal do not take the pointer coordinates as inout arguments any more, but as normal in ones.

See: `gtk_tree_view_get_tooltip_context()`, `gtk_icon_view_get_tooltip_context()`

### Adapt to GtkPopover changes

In GTK 3, a `GtkPopover` could be attached to any widget, using the `relative-to` property. This is no longer possible in GTK 4. The parent widget has to be aware of its popover children, and manage their size allocation. Therefore, only widgets with dedicated popover support can have them, such as `GtkMenuButton` or `GtkPopoverMenuBar`.

If you want to make a custom widget that has an attached popover, you need to call `gtk_popover_present()` in your `Gtk.WidgetClass.size_allocate` vfunc, in order to update the positioning of the popover.

### Stop using GtkFileChooserButton

The `GtkFileChooserButton` widget was removed, due to its shortcomings in the user interaction. You can replace it with a simple `GtkButton` that shows a `GtkFileChooserNative` dialog when clicked; once the file selection has completed, you can update the label of the `GtkButton` with the selected file.

### Adapt to changed GtkSettings properties

In GTK 3 the `GtkSettings:gtk-cursor-aspect-ratio` property of `GtkSettings` was a `float`. In GTK 4 this has been changed to a `double`.

## Changes to consider after the switch

GTK 4 has a number of new features that you may want to take advantage of once the dust has settled over the initial migration.

### Consider porting to the new list widgets

In GTK 2 and 3, `GtkTreeModel` and `GtkCellRenderer` and widgets using these were the primary way of displaying data and lists. GTK 4 brings a new family of widgets for this purpose that uses list models instead of tree models, and widgets instead of cell renderers.

To learn more about the new list widgets, you can read the List Widget Overview.