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GTK+ Reference Manual | ![]() |
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Common QuestionsCommon Questions — Find answers to common questions in the GTK+ manual |
This is an "index" of the reference manual organized by common "How do I..." questions. If you aren't sure which documentation to read for the question you have, this list is a good place to start.
1. General | |||||||
1.1. | How do I get started with GTK+? |
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The GTK+ website offers a tutorial and a FAQ. More documentation ranging from whitepapers to online books can be found at the GNOME developer's site. After studying these materials you should be well prepared to come back to this reference manual for details. |
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1.2. | Where can I get help with GTK+, submit a bug report, or make a feature request? |
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See the documentation on this topic. |
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1.3. | How do I port from one GTK+ version to another? |
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See the list of incompatible changes from 1.2 to 2.0. Also, the GNOME 2.0 porting guide on http://developer.gnome.org has some more detailed discussion of porting from 1.2 to 2.0. You may also find useful information in the documentation for specific widgets and functions. If you have a question not covered in the manual, feel free to ask on the mailing lists and please file a bug report against the documentation. |
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1.4. | How does memory management work in GTK+? Should I free data returned from functions? |
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See the documentation for GObject and GtkObject. For GObject note
specifically
For strings returned from functions, they will be declared "const" (using
G_CONST_RETURN) if they should not be freed. Non-const strings should be
freed with |
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1.5. | Why does my program leak memory, if I destroy a widget immediately after creating it ? |
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If GtkFoo isn't a toplevel window, then foo = gtk_foo_new (); gtk_widget_destroy (foo); is a memory leak, because no one assumed the initial floating reference. If you are using a widget and you aren't immediately packing it into a container, then you probably want standard reference counting, not floating reference counting. To to get this, you must acquire a reference to the widget and drop the floating reference (“ref and sink” in GTK+ parlance) after creating it: foo = gtk_foo_new (); g_object_ref (foo); gtk_object_sink (GTK_OBJECT (foo));
When you want to get rid of the widget, you must call gtk_widget_destroy (foo); g_object_unref (foo);
When you immediately add a widget to a container, it takes care of
assuming the initial floating reference and you don't have to worry
about reference counting at all ... just call |
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1.6. | How do I use GTK+ with threads? |
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This is covered in the GDK threads documentation. See also the GThread documentation for portable threading primitives. |
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1.7. | How do I internationalize a GTK+ program? |
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Most people use GNU
gettext, already required in order to install GLib. On a UNIX
or Linux system with gettext installed, type
The short checklist on how to use gettext is: call #define _(x) gettext (x) #define N_(x) x
You use
Nowadays, GLib provides the common shorthand macros in the header file
Code using these macros ends up looking like this: #include <gi18n.h> static const char *global_variable = N_("Translate this string"); static void make_widgets (void) { GtkWidget *label1; GtkWidget *label2; label1 = gtk_label_new (_("Another string to translate")); label2 = gtk_label_new (_(global_variable)); ...
Libraries using gettext should use #define _(x) dgettext ("MyDomain", x)
Again, GLib comes with the |
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1.8. | How do I use non-ASCII characters in GTK+ programs ? |
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GTK+ uses Unicode (more exactly UTF-8) for all text. UTF-8 encodes each Unicode codepoint as a sequence of one to six bytes and has a number of nice properties which make it a good choice for working with Unicode text in C programs:
More information about Unicode and UTF-8 can be found in the
UTF-8 and Unicode i
FAQ for Unix/Linux.
GLib provides functions for converting strings between UTF-8 and other
encodings, see
Text coming from external sources (e.g. files or user input), has to be
converted to UTF-8 before being handed over to GTK+. The following example
writes the content of a IS0-8859-1 encoded text file to
gchar *text, *utf8_text; gsize length; GError *error = NULL; if (g_file_get_contents (filename, &text, &length, NULL)) { utf8_text = g_convert (text, length, "UTF-8", "ISO-8859-1", NULL, NULL, &error); if (error != NULL) { fprintf ("Couldn't convert file %s to UTF-8\n", filename); g_error_free (error); } else g_print (utf8_text); } else fprintf (stderr, "Unable to read file %s\n", filename);
For string literals in the source code, there are several alternatives for handling non-ASCII content:
Here is an example showing the three approaches using the copyright sign © which has Unicode and ISO-8859-1 codepoint 169 and is represented in UTF-8 by the two bytes 194, 169: g_print ("direct UTF-8: ©"); g_print ("escaped UTF-8: \302\251"); text = g_convert ("runtime conversion: ©", -1, "ISO-8859-1", "UTF-8", NULL, NULL, NULL); g_print(text); g_free (text);
If you are using |
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1.9. | How do I use GTK+ with C++? |
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There are two ways to approach this. The GTK+ header files use the subset of C that's also valid C++, so you can simply use the normal GTK+ API in a C++ program. Alternatively, you can use a "C++ binding" such as gtkmm which provides a native C++ API. When using GTK+ directly, keep in mind that only functions can be connected to signals, not methods. So you will need to use global functions or "static" class functions for signal connections. Another common issue when using GTK+ directly is that C++ will not implicitly convert an integer to an enumeration. This comes up when using bitfields; in C you can write the following code: gdk_window_set_events (gdk_window, GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK); while in C++ you must write: gdk_window_set_events (gdk_window, (GdkEventMask) GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK); There are very few functions that require this cast, however. |
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1.10. | How do I use GTK+ with other non-C languages? |
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See the list of language bindings on http://www.gtk.org. |
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1.11. | How do I load an image or animation from a file? |
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To load an image file straight into a display widget, use
To load an image or animation file asynchronously (without blocking), use GdkPixbufLoader. |
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1.12. | How do I draw text ? |
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To draw a piece of text, use a Pango layout and layout = gtk_widget_create_pango_layout (widget, text); fontdesc = pango_font_description_from_string ("Luxi Mono 12"); pango_layout_set_font_description (layout, fontdesc); gdk_draw_layout (..., layout); pango_font_description_free (fontdesc); g_object_unref (layout);
Do not use the deprecated GdkFont and See also the "Text Handling in GTK 2" section of Porting applications to the GNOME 2.0 platform. |
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1.13. | How do I measure the size of a piece of text ? |
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To obtain the size of a piece of text, use a Pango layout and
layout = gtk_widget_create_pango_layout (widget, text); fontdesc = pango_font_description_from_string ("Luxi Mono 12"); pango_layout_set_font_description (layout, fontdesc); pango_layout_get_pixel_size (layout, &width, &height); pango_font_description_free (fontdesc); g_object_unref (layout);
Do not use the deprecated function See also the "Text Handling in GTK 2" section of Porting applications to the GNOME 2.0 platform. |
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1.14. |
Why are types not registered if I use their |
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The A common workaround for this problem is to store the result in a volatile variable, which keeps the compiler from optimizing the call away. volatile GType dummy = GTK_TYPE_BLAH;
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1.15. | How do I create a transparent toplevel window ? |
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To make a window transparent, it needs to use a visual which supports that.
This is done by getting the RGBA colormap of the screen with
GdkColormap *colormap; colormap = gdk_screen_get_rgba_colormap (screen); if (!colormap) colormap = gdk_screen_get_rgb_colormap (screen); gtk_widget_set_colormap (widget, colormap);
One possibility to fill the alpha channel on the window is to use
Note that the presence of an RGBA visual is no guarantee that the
window will actually appear transparent on screen. On X11, this
requires a compositing manager to be running. See
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2. Which widget should I use... | |||||||
2.1. | ...for lists and trees? |
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See tree widget overview — you should use the GtkTreeView widget. (A list is just a tree with no branches, so the tree widget is used for lists as well.) Do not use the deprecated widgets GtkTree or GtkCList/GtkCTree in newly-written code, they are less flexible and result in an inferior user interface. |
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2.2. | ...for multi-line text display or editing? |
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See text widget overview — you should use the GtkTextView widget. Do not use the deprecated widget GtkText in newly-written code, it has a number of problems that are best avoided.
If you only have a small amount of text, GtkLabel may also be appropriate
of course. It can be made selectable with |
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2.3. | ...to display an image or animation? |
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GtkImage can display images in just about any format GTK+ understands. You can also use GtkDrawingArea if you need to do something more complex, such as draw text or graphics over the top of the image. |
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2.4. | ...for presenting a set of mutually-exclusive choices, where Windows would use a combo box? |
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With GTK+, a GtkComboBox is the recommended widget to use for this use case. This widget looks like either a combo box or the current option menu, depending on the current theme. If you need an editable text entry, use GtkComboBoxEntry. |
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3. GtkWidget | |||||||
3.1. | How do I change the color of a widget? |
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See To change the background color for widgets such as GtkLabel that have no background, place them in a GtkEventBox and set the background of the event box. |
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3.2. | How do I change the font of a widget? |
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This has several possible answers, depending on what exactly you want to
achieve. One option is PangoFontDesc *font_desc = pango_font_description_new (); pango_font_description_set_size (font_desc, 40); gtk_widget_modify_font (widget, font); pango_font_description_free (font_desc);
If you want to make the text of a label larger, you can use
gtk_label_set_markup (label, "<big>big text</big>");
This is preferred for many apps because it's a relative size to the
user's chosen font size. See You can also change the font of a widget by putting gtk-font-name = "Sans 30"
in a resource file and parsing it with |
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3.3. | How do I disable/ghost/desensitize a widget? |
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In GTK+ a disabled widget is termed "insensitive." See
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4. GtkTextView | |||||||
4.1. | How do I get the contents of the entire text widget as a string? |
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See
GtkTextIter start, end; GtkTextBuffer *buffer; char *text; buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (text_view)); gtk_text_buffer_get_bounds (buffer, &start, &end); text = gtk_text_iter_get_text (&start, &end); /* use text */ g_free (text);
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4.2. | How do I make a text widget display its complete contents in a specific font? |
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If you use
To ensure that all text has the desired appearance, use |
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4.3. | How do I make a text view scroll to the end of the buffer automatically ? |
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A good way to keep a text buffer scrolled to the end is to place a mark at the end of the buffer, and give it right gravity. The gravity has the effect that text inserted at the mark gets inserted before, keeping the mark at the end.
To ensure that the end of the buffer remains visible, use
The gtk-demo application contains an example of this technique. |
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5. GtkTreeView | |||||||
5.1. | How do I associate some data with a row in the tree? |
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Remember that the GtkTreeModel columns don't necessarily have to be displayed.
So you can put non-user-visible data in your model just like any other data,
and retrieve it with |
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5.2. |
What's the GtkTreeView equivalent of |
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As there is no separate data column in the GtkTreeModel, there's no
built in function to find the iter from data. You can write a custom
searching function to walk the tree and find the data, or use
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5.3. | How do I put an image and some text in the same column? |
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You can pack more than one GtkCellRenderer into a single GtkTreeViewColumn
using |
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5.4. |
I can set data easily on my GtkTreeStore/GtkListStore models using
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Both the GtkTreeStore and the GtkListStore implement the GtkTreeModel
interface. Consequentially, the can use any function this interface
implements. The easiest way to read a set of data back is to use
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5.5. | How do I change the way that numbers are formatted by GtkTreeView? |
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Use The following example demonstrates this: enum { DOUBLE_COLUMN, N_COLUMNS }; GtkListStore *mycolumns; GtkTreeView *treeview; void my_cell_double_to_text (GtkTreeViewColumn *tree_column, GtkCellRenderer *cell, GtkTreeModel *tree_model, GtkTreeIter *iter, gpointer data) { GtkCellRendererText *cell_text = (GtkCellRendererText *)cell; gdouble d; gchar *text; /* Get the double value from the model. */ gtk_tree_model_get (tree_model, iter, (gint)data, &d, -1); /* Now we can format the value ourselves. */ text = g_strdup_printf ("%.2f", d); g_object_set (cell, "text", text, NULL); g_free (text); } void set_up_new_columns (GtkTreeView *myview) { GtkCellRendererText *renderer; GtkTreeViewColumn *column; GtkListStore *mycolumns; /* Create the data model and associate it with the given TreeView */ mycolumns = gtk_list_store_new (N_COLUMNS, G_TYPE_DOUBLE); gtk_tree_view_set_model (myview, GTK_TREE_MODEL (mycolumns)); /* Create a GtkCellRendererText */ renderer = gtk_cell_renderer_text_new (); /* Create a new column that has a title ("Example column"), * uses the above created renderer that will render the double * value into text from the associated model's rows. */ column = gtk_tree_view_column_new (); gtk_tree_view_column_set_title (column, "Example column"); renderer = gtk_cell_renderer_text_new (); gtk_tree_view_column_pack_start (column, renderer, TRUE); /* Append the new column after the GtkTreeView's previous columns. */ gtk_tree_view_append_column (GTK_TREE_VIEW (myview), column); /* Since we created the column by hand, we can set it up for our * needs, e.g. set its minimum and maximum width, etc. */ /* Set up a custom function that will be called when the column content * is rendered. We use the func_data pointer as an index into our * model. This is convenient when using multi column lists. */ gtk_tree_view_column_set_cell_data_func (column, renderer, my_cell_double_to_text, (gpointer)DOUBLE_COLUMN, NULL); }
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5.6. | How do I hide the expander arrows in my tree view ? |
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Set the expander-column property of the tree view to a hidden column.
See |
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6. Using cairo with GTK+ | |||||||
6.1. | How do I use cairo to draw in GTK+ applications ? |
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USe |
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6.2. |
I have created a cairo context with |
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All drawing in GTK+ is normally done in an expose handler, and GTK+ creates a temporary pixmap for double-buffering the drawing. If you create a cairo context outside the expose handler, it is backed by the GDK window itself, not the double-buffering pixmap. Consequently, any drawing you do with that cairo context gets overwritten at the end of the expose handler, when the double-buffering pixmap is copied back. Possible solutions to this problem are:
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6.3. | Can I improve the performance of my application by using the Glitz backend of cairo ? |
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No. The GDK X11 backend uses the cairo X backend (and the other GDK backends use their respective native cairo backends). The GTK+ developers believe that the best way to improving the GDK drawing performance is to optimize the cairo X backend and the relevant code paths in the X server that is uses (mostly the Render extension). |
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6.4. | Can I use cairo to draw on a GdkPixbuf ? |
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No, at least not yet. The cairo image surface does not support the pixel format used by GdkPixbuf. |
[1] If the file load fails,
gtk_image_new_from_file()
will display no image graphic — to detect
a failed load yourself, use gdk_pixbuf_new_from_file()
directly, then
gtk_image_new_from_pixbuf()
.