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<H2><A NAME="s6">6. Development with GTK+: widget specific questions </A></H2>
<H2><A NAME="ss6.1">6.1 How do I find out about the selection of a GtkList?</A>
</H2>
<P>Get the selection something like this:
<BLOCKQUOTE><CODE>
<PRE>
GList *sel;
sel = GTK_LIST(list)->selection;
</PRE>
</CODE></BLOCKQUOTE>
<P>This is how GList is defined (quoting glist.h):
<BLOCKQUOTE><CODE>
<PRE>
typedef struct _GList GList;
struct _GList
{
gpointer data;
GList *next;
GList *prev;
};
</PRE>
</CODE></BLOCKQUOTE>
<P>A GList structure is just a simple structure for doubly linked lists.
there exist several g_list_*() functions to modify a linked list in
glib.h. However the GTK_LIST(MyGtkList)->selection is maintained
by the gtk_list_*() functions and should not be modified.
<P>The selection_mode of the GtkList determines the selection
facilities of a GtkList and therefore the contents
of GTK_LIST(AnyGtkList)->selection:
<P>
<PRE>
selection_mode GTK_LIST()->selection contents
------------------------------------------------------
GTK_SELECTION_SINGLE selection is either NULL
or contains a GList* pointer
for a single selected item.
GTK_SELECTION_BROWSE selection is NULL if the list
contains no widgets, otherwise
it contains a GList* pointer
for one GList structure.
GTK_SELECTION_MULTIPLE selection is NULL if no listitems
are selected or a a GList* pointer
for the first selected item. that
in turn points to a GList structure
for the second selected item and so
on.
GTK_SELECTION_EXTENDED selection is NULL.
</PRE>
<P>The data field of the GList structure GTK_LIST(MyGtkList)->selection points
to the first GtkListItem that is selected. So if you would like to determine
which listitems are selected you should go like this:
<P>Upon Initialization:
<BLOCKQUOTE><CODE>
<PRE>
{
gchar *list_items[]={
"Item0",
"Item1",
"foo",
"last Item",
};
guint nlist_items=sizeof(list_items)/sizeof(list_items[0]);
GtkWidget *list_item;
guint i;
list=gtk_list_new();
gtk_list_set_selection_mode(GTK_LIST(list), GTK_SELECTION_MULTIPLE);
gtk_container_add(GTK_CONTAINER(AnyGtkContainer), list);
gtk_widget_show (list);
for (i = 0; i < nlist_items; i++)
{
list_item=gtk_list_item_new_with_label(list_items[i]);
gtk_object_set_user_data(GTK_OBJECT(list_item), (gpointer)i);
gtk_container_add(GTK_CONTAINER(list), list_item);
gtk_widget_show(list_item);
}
}
</PRE>
</CODE></BLOCKQUOTE>
<P>To get known about the selection:
<BLOCKQUOTE><CODE>
<PRE>
{
GList *items;
items=GTK_LIST(list)->selection;
printf("Selected Items: ");
while (items) {
if (GTK_IS_LIST_ITEM(items->data))
printf("%d ", (guint)
gtk_object_get_user_data(items->data));
items=items->next;
}
printf("\n");
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.2">6.2 How do I stop the column headings of a GtkCList disappearing</A>
when the list is scrolled?</H2>
<P>This happens when a GtkCList is packed into a GtkScrolledWindow using
the function <CODE>gtk_scroll_window_add_with_viewport()</CODE>. The prefered
method of adding a CList to a scrolled window is to use the function
<CODE>gtk_container_add</CODE>, as in:
<P>
<BLOCKQUOTE><CODE>
<PRE>
GtkWidget *scrolled, *clist;
char *titles[] = { "Title1" , "Title2" };
scrolled = gtk_scrolled_window_new(NULL, NULL);
clist = gtk_clist_new_with_titles(2, titles);
gtk_container_add(GTK_CONTAINER(scrolled), clist);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<P>
<H2><A NAME="ss6.3">6.3 I don't want the user of my applications to enter text into a GtkCombo. Any idea?</A>
</H2>
<P>A GtkCombo has an associated entry which can be accessed using the
following expression:
<P>
<BLOCKQUOTE><CODE>
<PRE>
GTK_COMBO(combo_widget)->entry
</PRE>
</CODE></BLOCKQUOTE>
<P>If you don't want the user to be able to modify the content of this
entry, you can use the gtk_entry_set_editable() function:
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_entry_set_editable(GtkEntry *entry,
gboolean editable);
</PRE>
</CODE></BLOCKQUOTE>
<P>Set the editable parameter to FALSE to disable typing into the entry.
<P>
<H2><A NAME="ss6.4">6.4 How do I catch a combo box change?</A>
</H2>
<P>The entry which is associated to your GtkCombo send a "changed" signal
when:
<UL>
<LI>some text is typed in</LI>
<LI>the selection of the combo box is changed</LI>
</UL>
<P>To catch any combo box change, simply connect your signal handler with
<P>
<BLOCKQUOTE><CODE>
<PRE>
gtk_signal_connect(GTK_COMBO(cb)->entry,
"changed",
GTK_SIGNAL_FUNC(my_cb_change_handler),
NULL);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.5">6.5 How can I define a separation line in a menu? </A>
</H2>
<P>See the
<A HREF="http://www.gtk.org/tutorial/">Tutorial</A> for information on how to create menus.
However, to create a separation line in a menu, just insert an
empty menu item:
<P>
<BLOCKQUOTE><CODE>
<PRE>
menuitem = gtk_menu_item_new();
gtk_menu_append(GTK_MENU(menu), menuitem);
gtk_widget_show(menuitem);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.6">6.6 How can I right justify a menu, such as Help? </A>
</H2>
<P>Depending on if you use the MenuFactory or not, there are two ways to
proceed. With the MenuFactory, use something like the following:
<P>
<BLOCKQUOTE><CODE>
<PRE>
menu_path = gtk_menu_factory_find (factory, "<MyApp>/Help");
gtk_menu_item_right_justify(menu_path->widget);
</PRE>
</CODE></BLOCKQUOTE>
<P>If you do not use the MenuFactory, you should simply use:
<P>
<BLOCKQUOTE><CODE>
<PRE>
gtk_menu_item_right_justify(my_menu_item);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.7">6.7 How do I add some underlined accelerators to menu items?</A>
</H2>
<P>Damon Chaplin, the technical force behind the Glade project, provided
the following code sample (this code is an output from Glade). It
creates a small <CODE>File</CODE> menu item with only one child
(<CODE>New</CODE>). The F in <CODE>File</CODE> and the N in <CODE>New</CODE> are underlined,
and the relevant accelerators are created.
<P>
<BLOCKQUOTE><CODE>
<PRE>
menubar1 = gtk_menu_bar_new ();
gtk_object_set_data (GTK_OBJECT (window1), "menubar1", menubar1);
gtk_widget_show (menubar1);
gtk_box_pack_start (GTK_BOX (vbox1), menubar1, FALSE, FALSE, 0);
file1 = gtk_menu_item_new_with_label ("");
tmp_key = gtk_label_parse_uline (GTK_LABEL (GTK_BIN (file1)->child),
_("_File"));
gtk_widget_add_accelerator (file1, "activate_item", accel_group,
tmp_key, GDK_MOD1_MASK, 0);
gtk_object_set_data (GTK_OBJECT (window1), "file1", file1);
gtk_widget_show (file1);
gtk_container_add (GTK_CONTAINER (menubar1), file1);
file1_menu = gtk_menu_new ();
file1_menu_accels = gtk_menu_ensure_uline_accel_group (GTK_MENU (file1_menu));
gtk_object_set_data (GTK_OBJECT (window1), "file1_menu", file1_menu);
gtk_menu_item_set_submenu (GTK_MENU_ITEM (file1), file1_menu);
new1 = gtk_menu_item_new_with_label ("");
tmp_key = gtk_label_parse_uline (GTK_LABEL (GTK_BIN (new1)->child),
_("_New"));
gtk_widget_add_accelerator (new1, "activate_item", file1_menu_accels,
tmp_key, 0, 0);
gtk_object_set_data (GTK_OBJECT (window1), "new1", new1);
gtk_widget_show (new1);
gtk_container_add (GTK_CONTAINER (file1_menu), new1);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.8">6.8 How can I retrieve the text from a GtkMenuItem?</A>
</H2>
<P>You can usually retrieve the label of a specific GtkMenuItem with:
<P>
<BLOCKQUOTE><CODE>
<PRE>
if (GTK_BIN (menu_item)->child)
{
GtkWidget *child = GTK_BIN (menu_item)->child;
/* do stuff with child */
if (GTK_IS_LABEL (child))
{
gchar *text;
gtk_label_get (GTK_LABEL (child), &text);
g_print ("menu item text: %s\n", text);
}
}
</PRE>
</CODE></BLOCKQUOTE>
<P>To get the active menu item from a GtkOptionMenu you can do:
<BLOCKQUOTE><CODE>
<PRE>
if (GTK_OPTION_MENU (option_menu)->menu_item)
{
GtkWidget *menu_item = GTK_OPTION_MENU (option_menu)->menu_item;
}
</PRE>
</CODE></BLOCKQUOTE>
<P>But, there's a catch. For this specific case, you can <B>not</B> get
the label widget from <CODE>menu_item</CODE> with the above code, because the
option menu reparents the menu_item's child temporarily to display the
currently active contents. So to retrive the child of the currently
active menu_item of an option menu, you'll have to do:
<P>
<BLOCKQUOTE><CODE>
<PRE>
if (GTK_BIN (option_menu)->child)
{
GtkWidget *child = GTK_BIN (option_menu)->child;
/* do stuff with child */
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.9">6.9 How do I right (or otherwise) justify a GtkLabel?</A>
</H2>
<P>Are you sure you want to <EM>justify</EM> the labels? The label class
contains the <CODE>gtk_label_set_justify()</CODE> function that is used to
control the justification of a multi-line label.
<P>What you probably want is to set the <EM>alignment</EM> of the label,
ie right align it, center it or left align it. If you want to do this,
you should use:
<P>
<BLOCKQUOTE><CODE>
<PRE>
void gtk_misc_set_alignment (GtkMisc *misc,
gfloat xalign,
gfloat yalign);
</PRE>
</CODE></BLOCKQUOTE>
<P>where the <CODE>xalign</CODE> and <CODE>yalign</CODE> values are floats in [0.00;1.00].
<P>
<BLOCKQUOTE><CODE>
<PRE>
GtkWidget *label;
/* horizontal : left align, vertical : top */
gtk_misc_set_alignment(GTK_MISK(label), 0.0f, 0.0f);
/* horizontal : centered, vertical : centered */
gtk_misc_set_alignment(GTK_MISK(label), 0.5f, 0.5f);
/* horizontal : right align, vertical : bottom */
gtk_misc_set_alignment(GTK_MISK(label), 1.0f, 1.0f);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.10">6.10 How do I set the background color of a GtkLabel widget?</A>
</H2>
<P>The Gtklabel widget is one of a few GTK+ widgets that don't create
their own window to render themselves into. Instead, they draw
themselves directly onto their parents window.
<P>This means that in order to set the background color for a GtkLabel
widget, you need to change the background color of its parent,
i.e. the object that you pack it into.
<P>
<H2><A NAME="ss6.11">6.11 How do I set the color and font of a GtkLabel using a Resource File?</A>
</H2>
<P>The widget name path constructed for a Label consists of the widget
names of its object hierarchy as well, e.g.
<P>
<PRE>
window (name: humphrey)
hbox
label (name: mylabel)
</PRE>
<P>The widget path your pattern needs to match would be:
<CODE>humphrey.GtkHBox.mylabel</CODE>
<P>The resource file may look something like:
<P>
<PRE>
style "title"
{
fg[NORMAL] = {1.0, 0.0, 0.0}
font = "-adobe-helvetica-bold-r-normal--*-140-*-*-*-*-*-*"
}
widget "*mylabel" style "title"
</PRE>
<P>In your program, you would also need to give a name to the Label
widget, which can be done using:
<PRE>
label = gtk_label_new("Some Label Text");
gtk_widget_set_name(label, "mylabel");
gtk_widget_show(label);
</PRE>
<P>
<H2><A NAME="ss6.12">6.12 How do I configure Tooltips in a Resource File?</A>
</H2>
<P>The tooltip's window is named "gtk-tooltips", GtkTooltips in itself is
not a GtkWidget (though a GtkObject) and as such is not attempted to
match any widget styles.
<P>So, you resource file should look something like:
<PRE>
style "postie"
{
bg[NORMAL] = {1.0, 1.0, 0.0}
}
widget "gtk-tooltips*" style "postie"
</PRE>
<P>
<H2><A NAME="ss6.13">6.13 I can't add more than (something like) 2000 chars in a GtkEntry. What's wrong?</A>
</H2>
<P>There is now a known problem in the GtkEntry widget. In the
<CODE>gtk_entry_insert_text()</CODE> function, the following lines limit
the number of chars in the entry to 2047.
<P>
<BLOCKQUOTE><CODE>
<PRE>
/* The algorithms here will work as long as, the text size (a
* multiple of 2), fits into a guint16 but we specify a shorter
* maximum length so that if the user pastes a very long text, there
* is not a long hang from the slow X_LOCALE functions. */
if (entry->text_max_length == 0)
max_length = 2047;
else
max_length = MIN (2047, entry->text_max_length);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.14">6.14 How do I make a GtkEntry widget activate on pressing the Return key?</A>
</H2>
<P>The Entry widget emits an 'activate' signal when you press return in
it. Just attach to the activate signal on the entry and do whatever you
want to do. Typical code would be:
<P>
<BLOCKQUOTE><CODE>
<PRE>
entry = gtk_entry_new();
gtk_signal_connect (GTK_OBJECT(entry), "activate",
GTK_SIGNAL_FUNC(entry_callback),
NULL);
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.15">6.15 How do I validate/limit/filter the input to a GtkEntry?</A>
</H2>
<P>If you want to validate the text that a user enters into a GtkEntry
widget you can attach to the "insert_text" signal of the entry, and
modify the text within the callback function. The example below forces
all characters to uppercase, and limits the range of characters to
A-Z. Note that the entry is cast to an object of type GtkEditable,
from which GtkEntry is derived.
<P>
<BLOCKQUOTE><CODE>
<PRE>
#include <ctype.h>
#include <gtk/gtk.h>
void insert_text_handler (GtkEntry *entry,
const gchar *text,
gint length,
gint *position,
gpointer data)
{
GtkEditable *editable = GTK_EDITABLE(entry);
int i, count=0;
gchar *result = g_new (gchar, length);
for (i=0; i < length; i++) {
if (!isalpha(text[i]))
continue;
result[count++] = islower(text[i]) ? toupper(text[i]) : text[i];
}
if (count > 0) {
gtk_signal_handler_block_by_func (GTK_OBJECT (editable),
GTK_SIGNAL_FUNC (insert_text_handler),
data);
gtk_editable_insert_text (editable, result, count, position);
gtk_signal_handler_unblock_by_func (GTK_OBJECT (editable),
GTK_SIGNAL_FUNC (insert_text_handler),
data);
}
gtk_signal_emit_stop_by_name (GTK_OBJECT (editable), "insert_text");
g_free (result);
}
int main (int argc,
char *argv[])
{
GtkWidget *window;
GtkWidget *entry;
gtk_init (&argc, &argv);
/* create a new window */
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_title(GTK_WINDOW (window), "GTK Entry");
gtk_signal_connect(GTK_OBJECT (window), "delete_event",
(GtkSignalFunc) gtk_exit, NULL);
entry = gtk_entry_new();
gtk_signal_connect(GTK_OBJECT(entry), "insert_text",
GTK_SIGNAL_FUNC(insert_text_handler),
NULL);
gtk_container_add(GTK_CONTAINER (window), entry);
gtk_widget_show(entry);
gtk_widget_show(window);
gtk_main();
return(0);
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.16">6.16 How do I use horizontal scrollbars with a GtkText widget?</A>
</H2>
<P>The short answer is that you can't. The current version of the GtkText
widget does not support horizontal scrolling. There is an intention to
completely rewrite the GtkText widget, at which time this limitation
will be removed.
<P>
<H2><A NAME="ss6.17">6.17 How do I change the font of a GtkText widget?</A>
</H2>
<P>There are a couple of ways of doing this. As GTK+ allows the
appearance of applications to be changed at run time using resources
you can use something like the following in the appropriate
file:
<P>
<BLOCKQUOTE><CODE>
<PRE>
style "text"
{
font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
}
</PRE>
</CODE></BLOCKQUOTE>
<P>Another way to do this is to load a font within your program, and then
use this in the functions for adding text to the text widget. You can
load a font using, for example:
<P>
<BLOCKQUOTE><CODE>
<PRE>
GdkFont *font;
font = gdk_font_load("-adobe-helvetica-medium-r-normal--*-140-*-*-*-*-*-*");
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H2><A NAME="ss6.18">6.18 How do I set the cursor position in a GtkText object?</A>
</H2>
<P>Notice that the response is valid for any object that inherits from the
GtkEditable class.
<P>Are you sure that you want to move the cursor position? Most of the
time, while the cursor position is good, the insertion point does not
match the cursor position. If this apply to what you really want, then
you should use the <CODE>gtk_text_set_point()</CODE> function. If you want to
set the insertion point at the current cursor position, use the
following:
<P>
<BLOCKQUOTE><CODE>
<PRE>
gtk_text_set_point(GTK_TEXT(text),
gtk_editable_get_position(GTK_EDITABLE(text)));
</PRE>
</CODE></BLOCKQUOTE>
<P>If you want the insertion point to follow the cursor at all time, you
should probably catch the button press event, and then move the
insertion point. Be careful : you'll have to catch it after the widget
has changed the cursor position though. Thomas Mailund Jensen proposed
the following code:
<P>
<BLOCKQUOTE><CODE>
<PRE>
static void
insert_bar (GtkWidget *text)
{
/* jump to cursor mark */
gtk_text_set_point (GTK_TEXT (text),
gtk_editable_get_position (GTK_EDITABLE (text)));
gtk_text_insert (GTK_TEXT (text), NULL, NULL, NULL,
"bar", strlen ("bar"));
}
int
main (int argc, char *argv[])
{
GtkWidget *window, *text;
gtk_init (&argc, &argv);
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
text = gtk_text_new (NULL, NULL);
gtk_text_set_editable (GTK_TEXT (text), TRUE);
gtk_container_add (GTK_CONTAINER (window), text);
/* connect after everything else */
gtk_signal_connect_after (GTK_OBJECT(text), "button_press_event",
GTK_SIGNAL_FUNC (insert_bar), NULL);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
</PRE>
</CODE></BLOCKQUOTE>
<P>Now, if you really want to change the cursor position, you should use the
<CODE>gtk_editable_set_position()</CODE> function.
<P>
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