faqs.html

gtk_text program sample&eg

        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z853">I want to use the arrow keys as a
            control in my application, but GTK+ keeps stealing the
            key press events to move the focus around.</a>
          </h2>
          <p>
            Key press handling is somewhat complex. You might want
            to read <a href="sec-gdkevent.html#SEC-GDKKEYFOCUS">the
            section called <i>Keyboard Focus</i> in the chapter
            called <i>GDK Basics</i></a> and <a href= 
            "z57.html#SEC-FOCUSWIDGET">the section called <i>
            Focus</i> in the chapter called <i>GTK+ Basics</i></a>
            for a brief overview. <a href= 
            "sec-gdkevent.html#SEC-GTKEVENTS">the section called
            <i>Receiving GDK Events in GTK+</i> in the chapter
            called <i>GDK Basics</i></a> is also relevant.
          </p>
          <p>
            In short, key events are initially received by a
            toplevel <tt class="CLASSNAME">GtkWindow</tt>. GTK+'s
            key event behavior is more or less defined by default
            key press event handler in <tt class="FILENAME">
            gtkwindow.c</tt> (looking at this function is
            instructive). It works as follows:
          </p>
          <ul>
            <li>
              <p>
                If there's a focus widget, the key event signal is
                emitted on the focus widget. If this emission
                returns <span class="STRUCTNAME">TRUE</span>, as
                described in <a href= 
                "sec-gdkevent.html#SEC-GTKEVENTS">the section
                called <i>Receiving GDK Events in GTK+</i> in the
                chapter called <i>GDK Basics</i></a>, processing
                stops.&#13;
              </p>
            </li>
            <li>
              <p>
                If any of the accelerator groups attached to the
                window contain an accelerator matching the event,
                then processing stops.&#13;
              </p>
            </li>
            <li>
              <p>
                If the key event hasn't been handled yet, there are
                some default bindings; the arrow keys move the
                focus around, for example.&#13;
              </p>
            </li>
          </ul>
          <p>
            Thus, to override the arrow key behavior, you can
            return <span class="STRUCTNAME">TRUE</span> from the
            focus widget's signal emission, install an accelerator
            for the arrow keys, or connect to <span class="SYMBOL">
            "key_press_event"</span> on the toplevel window and use
            <tt class="FUNCTION">
            gtk_signal_emit_stop_by_name()</tt> to end the signal
            emission before the <tt class="CLASSNAME">
            GtkWindow</tt> default handler runs.
          </p>
        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z854">Does GTK+ have multiple inheritance?</a>
          </h2>
          <p>
            No, but "interfaces" (in Java terms) or "pure virtual
            classes" (in C++ terms) are planned for the next
            version. See <a href="z144.html#SEC-OVERRIDESIGNALS">
            the section called <i>Overridable Signals</i> in the
            chapter called <i>Writing a <tt class="CLASSNAME">
            GtkWidget</tt></i></a> for a discussion of an ugly
            workaround used in <tt class="CLASSNAME">GtkWidget</tt>
            to create "activatable" and "scrollable" interfaces.
          </p>
        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z855">I'm getting error messages from GDK. How
            can I determine the cause of these?</a>
          </h2>
          <p>
            First, run your program with the <tt class=
            "APPLICATION">--sync</tt> option. This invokes <tt
            class="FUNCTION">XSynchronize()</tt> to turn off event
            buffering; it slows down the application, but causes
            errors to be reported as soon as they occur.
            Alternatively, some Xlib implementations let you turn
            on synchronization by setting the global variable <span
            class="STRUCTNAME">_Xdebug</span> to <span class= 
            "STRUCTNAME">TRUE</span> in a debugger.
          </p>
          <p>
            Once errors are being reported synchronously, just run
            your app in a debugger and wait for <tt class=
            "FUNCTION">abort()</tt> to be called. For warnings, set
            a breakpoint at <tt class="FUNCTION">g_logv()</tt>
            which is the function called by the <tt class=
            "FUNCTION">g_warning()</tt> macro.
          </p>
        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z856">How do I update the GUI without
            returning control to the main loop?</a>
          </h2>
          <p>
            Just do this:
          </p>
          <table border="0" bgcolor="#E0E0E0" width="100%">
            <tr>
              <td>
<pre class="PROGRAMLISTING">
&#13; while (gtk_events_pending())
   gtk_main_iteration();&#13;
</pre>
              </td>
            </tr>
          </table>
          <p>
            This code will handle all pending events, then return
            control to you. You can also run nested instances of
            <tt class="FUNCTION">gtk_main()</tt>; each call to <tt
            class="FUNCTION">gtk_main_quit()</tt> exits one
            instance. <tt class="FUNCTION">gnome_dialog_run()</tt>
            uses this technique to block waiting for user input.
          </p>
        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z857">How should I format code to be included
            in GTK+ or Gnome?</a>
          </h2>
          <p>
            The GTK+ coding style is basically the GNU coding style
            (<a href="http://www.gnu.org/prep/standards_toc.html"
            target=
            "_top">http://www.gnu.org/prep/standards_toc.html</a>).
            The Gnome libraries are less consistent, but lean
            toward the Linux kernel coding style (documented in <tt
            class="FILENAME">
            /usr/src/linux/Documentation/CodingStyle</tt> on many
            Linux systems).
          </p>
          <p>
            The GTK+ style uses two-space indentation, puts all
            braces on a new line, and leaves one space between
            identifiers and opening parentheses, like this:
          </p>
          <table border="0" bgcolor="#E0E0E0" width="100%">
            <tr>
              <td>
<pre class="PROGRAMLISTING">
&#13;if (whatever)
  {
    foo (arg1, arg2);
  }&#13;
</pre>
              </td>
            </tr>
          </table>
          <p>
            Emacs uses this style by default.
          </p>
          <p>
            The Gnome style uses eight-space indentation and
            Kernighan and Ritchie braces, like so:
          </p>
          <table border="0" bgcolor="#E0E0E0" width="100%">
            <tr>
              <td>
<pre class="PROGRAMLISTING">
&#13;if (whatever) {
        foo (arg1, arg2); 
}&#13;
</pre>
              </td>
            </tr>
          </table>
          <p>
            It also leaves a space between identifiers and opening
            parentheses. To make Emacs use the Gnome style, add a
            line like this to the top of your source files:
          </p>
          <table border="0" bgcolor="#E0E0E0" width="100%">
            <tr>
              <td>
<pre class="PROGRAMLISTING">
&#13;/* -*- Mode: C; indent-tabs-mode: nil; c-basic-offset: 8 c-style: "K&amp;R" -*- */&#13;
</pre>
              </td>
            </tr>
          </table>
          <p>
            When preparing a patch for any piece of free software,
            it's polite the style of the preexisting code. It's
            customary to include a file called <tt class=
            "FILENAME">HACKING</tt> in source code distributions
            addressing this and similar issues; read it if it
            exists.
          </p>
        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z858">Is there a GUI builder for GTK+ and
            Gnome?</a>
          </h2>
          <p>
            A very promising GUI builder called Glade is being
            developed. Glade can generate source code in several
            languages, or an XML description of your widgets. An
            add-on module called <tt class="APPLICATION">
            libglade</tt> loads these XML descriptions at runtime
            and creates the described widgets. The next release of
            the Gnome libraries will very likely include or require
            <tt class="APPLICATION">libglade</tt>.
          </p>
        </div>
        <div class="SECT2">
          <h2 class="SECT2">
            <a name="Z859">How well do GTK+ and Gnome support
            internationalization?</a>
          </h2>
          <p>
            GTK+ 1.2 supports most European and Asian languages.
            GDK contains an API for loading fontsets and rendering
            multibyte strings, though this book does not cover it.
            The stock GTK+ widgets that handle text use this API
            and will deal with multibyte strings correctly. GTK+
            also supports input methods for Asian languages. GTK+
            1.2 does <i class="EMPHASIS">not</i> support
            right-to-left scripts, or scripts that require complex
            ligatures and unusual line breaks. However, support for
            these languages is a high priority for GTK+ 1.4. For
            details on future plans, Owen Taylor's white paper at
            <a href=
            "http://developer.gnome.org/doc/whitepapers/gtki18n/"
            target="_top">
            http://developer.gnome.org/doc/whitepapers/gtki18n/</a> is
            an excellent resource.
          </p>
          <p>
            Both GTK+ and Gnome use the <tt class="APPLICATION">
            gettext</tt> message catalog system to translate
            user-visible strings, so any string the toolkit knows
            how to render can be translated into foreign languages.
            <a href="sec-i18n.html">the section called <i>
            Internationalization</i> in the chapter called <i>Gnome
            Application Basics</i></a> covers this topic.
          </p>
        </div>
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