Migrating from GTK 3.x to GTK 4

Preparation in GTK 3.x
Do not use deprecated symbols
Enable diagnostic warnings
Do not use widget style properties
Review your window creation flags
Stop using direct access to GdkEvent structs
Stop using gdk_pointer_warp()
Stop using non-RGBA visuals
Stop using GtkBox padding, fill and expand child properties
Stop using the state argument of GtkStyleContext getters
Stop using gdk_pixbuf_get_from_window() and gdk_cairo_set_source_surface()
Stop using GtkWidget event signals
Set a proper application ID
Stop using gtk_main() and related APIs
Reduce the use of gtk_widget_destroy()
Reduce the use of generic container APIs</title>
Changes that need to be done at the time of the switch
Stop using GdkScreen
Stop using the root window
Stop using GdkVisual
Stop using GdkDeviceManager
Adapt to GdkWindow API changes
The iconified window state has been renamed to minimized
Adapt to GdkEvent API changes
Stop using grabs
Adapt to coordinate API changes
Adapt to GdkKeymap API changes
Adapt to changes in keyboard modifier handling
Stop using gtk_get_current_… APIs
Convert your ui files
Adapt to event controller API changes
Focus handling changes
Use the new apis for keyboard shortcuts
Stop using GtkEventBox
Stop using GtkButtonBox
Adapt to GtkBox API changes
Adapt to GtkHeaderBar and GtkActionBar API changes
Adapt to GtkStack, GtkAssistant and GtkNotebook API changes
Adapt to GtkBin removal
Adapt to GtkContainer removal
Stop using GtkContainer::border-width
Adapt to gtk_widget_destroy() removal
Adapt to coordinate API changes
Adapt to GtkStyleContext API changes
Adapt to GtkCssProvider API changes
Stop using GtkShadowType and GtkRelief properties
Adapt to GtkWidget’s size request changes
Adapt to GtkWidget’s size allocation changes
Switch to GtkWidget’s children APIs
Don’t use -gtk-gradient in your CSS
Don’t use -gtk-icon-effect in your CSS
Don’t use -gtk-icon-theme in your CSS
Don’t use -gtk-outline-…-radius in your CSS
Adapt to drawing model changes
Stop using APIs to query GdkSurfaces
Widgets are now visible by default
Adapt to changes in animated hiding and showing of widgets
Stop passing commandline arguments to gtk_init
GdkPixbuf is deemphasized
GtkWidget event signals are removed
Invalidation handling has changed
Stop using GtkWidget::draw
Window content observation has changed
Monitor handling has changed
Adapt to cursor API changes
Adapt to icon size API changes
Adapt to changes in the GtkAssistant API
Adapt to changes in the API of GtkEntry, GtkSearchEntry and GtkSpinButton
Adapt to changes in GtkOverlay API
Use GtkFixed instead of GtkLayout
Adapt to search entry changes
Stop using gtk_window_activate_default()
Stop setting ::has-default and ::has-focus in .ui files
Stop using the GtkWidget::display-changed signal
GtkPopover::modal has been renamed to autohide
gtk_widget_get_surface has been removed
gtk_widget_is_toplevel has been removed
gtk_widget_get_toplevel has been removed
GtkEntryBuffer ::deleted-text has changed
GtkMenu, GtkMenuBar and GtkMenuItem are gone
GtkToolbar has been removed
GtkAspectFrame is no longer a frame
Stop using custom tooltip windows
Switch to the new Drag-and-Drop api
Adapt to GtkIconTheme API changes
Update to GtkFileChooser API changes
Stop using blocking dialog functions

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 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 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 the “margin” properties on your GtkBox child widgets.

The fill child property can be replaced by setting appropriate values for the “halign” and “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 “hexpand” or “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 “hexpand” or “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_surface()

These functions are not supported in GTK 4. Instead, either use backend-specific APIs, or render your widgets using GtkWidgetClass.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 GtkGestures replace event signals in GTK 4. They have been backported to GTK 3.x so you can prepare for this change.

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 mainloop 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().

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().

Reduce the use of generic container APIs</title>

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_box_pack_start() or gtk_grid_attach(), and thereby reduce the amount of work you have to do at the time of the switch.