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Gtk+/Gnome Application Development
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Finishing Touches

The difference between a good dialog and a great dialog is in the details. GnomeDialog comes with a number of features to make that final polish easy. Figure 4 sums them up.

       #include <libgnomeui/gnome-dialog.h>

void gnome_dialog_set_parent(GnomeDialog* dialog, GtkWindow* parent);

void gnome_dialog_set_default(GnomeDialog* dialog, gint button);

void gnome_dialog_editable_enters(GnomeDialog* dialog, GtkEditable* editable);

void gnome_dialog_set_sensitive(GnomeDialog* dialog, gint button, gboolean setting);

Figure 4. GnomeDialog Polish

Dialogs have a logical parent, usually the main application window. You can tell the library about this parent-child relationship; this lets Gnome honor certain user preferences, and in turn indicates the relationship to the window manager. Most window managers will minimize child dialogs when the parent window is minimized, and keep child dialogs on top of their parent.

It's important to use gnome_dialog_set_parent() with transient dialogs only. A transient dialog is one that appears and is dismissed relatively quickly. (GnomeDialog is really meant for transient dialogs.) Some "dialogs" are just small windows, such as the tool palette in the Gimp. These persistent ("floating") dialogs should be minimizable without minimizing the parent, and they should not be forced to stay above the parent window.

Your dialog should have a sensible default button---this is the button activated when the user presses the Enter key. gnome_dialog_set_default() specifies the default button. It's a judgment call which button should be the default. Often the best choice is the least-destructive action (i.e., "Cancel" rather than "OK"), but if neither is destructive, user convenience might guide your decision.

Typically, operations such as deleting data or quitting an application have "Cancel" or "No" as the default; dialogs that ask the user to enter text or other information typically have "OK" as the default. Remember that many window managers will focus windows when they pop up, so keystrokes users intend to go to their current application might go to your dialog instead. If your dialog has "delete all my files" as the default button, you will get hate mail.

Editable widgets emit the "activate" signal when Enter is pressed. Typically users expect Enter to activate the default dialog button, but if you have an editable widget such as GtkEntry in your dialog, it will capture any Enter presses, and keep the dialog's buttons from responding to them. gnome_dialog_editable_enters() activates the dialog's default button when the GtkEditable is activated, solving the problem.

gnome_dialog_set_sensitive() calls gtk_widget_set_sensitive() on button. If clicking a button makes no sense at a given time it should be desensitized.

Finally, you should make sure you do not create multiple instances of a dialog. Many applications allow you to pop up multiple Preferences or About dialogs; users will not trigger this bug very often, but it is a nice touch to avoid the problem. The following code deals with it in a simple way (note that the details of creating and showing the dialog have been omitted).

  static GtkWidget* dialog = NULL;

  if (dialog != NULL) 
      /* This code tries to de-iconify and raise the dialog. 
       * It assumes the dialog is realized; if you can't 
       * ensure that, check that dialog->window != NULL.

      dialog = gnome_dialog_new();      /* Arguments elided. */


      /* Show the dialog, connect callbacks, etc. here */                   

gtk_widget_destroyed() is defined in gtk/gtkwidget.h, and simply assigns NULL to its second argument. The code resets the dialog variable each time the user closes the dialog, and raises/deiconifies the dialog if the user tries to open it while another one is active. Note that the window manager has some say in whether the raise/deiconify is successful, so it is not guaranteed to happen.

Gtk+/Gnome Application Development
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  Published under free license. Design by Interspire