<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Signal Emission and Propagation</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="GTK+ 2.0 Tutorial" HREF="book1.html"><LINK REL="UP" TITLE="Advanced Event and Signal Handling" HREF="c1797.html"><LINK REL="PREVIOUS" TITLE="Advanced Event and Signal Handling" HREF="c1797.html"><LINK REL="NEXT" TITLE="Managing Selections" HREF="c1834.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >GTK+ 2.0 Tutorial</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="c1797.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Advanced Event and Signal Handling</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="c1834.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SEC-SIGNALEMISSIONANDPROPAGATION" >Signal Emission and Propagation</A ></H1 ><P >Signal emission is the process whereby GTK runs all handlers for a specific object and signal.</P ><P >First, note that the return value from a signal emission is the return value of the <I CLASS="EMPHASIS" >last</I > handler executed. Since event signals are all of type <TT CLASS="LITERAL" >GTK_RUN_LAST</TT >, this will be the default (GTK supplied) handler, unless you connect with gtk_signal_connect_after().</P ><P >The way an event (say "button_press_event") is handled, is:</P ><P ></P ><UL ><LI ><P >Start with the widget where the event occured.</P ></LI ><LI ><P >Emit the generic "event" signal. If that signal handler returns a value of TRUE, stop all processing.</P ></LI ><LI ><P >Otherwise, emit a specific, "button_press_event" signal. If that returns TRUE, stop all processing.</P ></LI ><LI ><P >Otherwise, go to the widget's parent, and repeat the above two steps.</P ></LI ><LI ><P >Continue until some signal handler returns TRUE, or until the top-level widget is reached.</P ></LI ></UL ><P >Some consequences of the above are:</P ><P ></P ><UL ><LI ><P >Your handler's return value will have no effect if there is a default handler, unless you connect with gtk_signal_connect_after().</P ></LI ><LI ><P >To prevent the default handler from being run, you need to connect with gtk_signal_connect() and use gtk_signal_emit_stop_by_name() - the return value only affects whether the signal is propagated, not the current emission.</P ></LI ></UL ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="c1797.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="book1.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="c1834.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Advanced Event and Signal Handling</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c1797.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Managing Selections</TD ></TR ></TABLE ></DIV ></BODY ></HTML >