<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Managing Selections</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="PREVIOUS" TITLE="Signal Emission and Propagation" HREF="x1810.html"><LINK REL="NEXT" TITLE="Retrieving the selection" HREF="x1850.html"></HEAD ><BODY CLASS="CHAPTER" 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="x1810.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x1850.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="CH-MANAGINGSELECTIONS" ></A >Managing Selections</H1 ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SEC-SELECTIONSOVERVIEW" >Overview</A ></H1 ><P >One type of interprocess communication supported by X and GTK is <I CLASS="EMPHASIS" >selections</I >. A selection identifies a chunk of data, for instance, a portion of text, selected by the user in some fashion, for instance, by dragging with the mouse. Only one application on a display (the <I CLASS="EMPHASIS" >owner</I >) can own a particular selection at one time, so when a selection is claimed by one application, the previous owner must indicate to the user that selection has been relinquished. Other applications can request the contents of a selection in different forms, called <I CLASS="EMPHASIS" >targets</I >. There can be any number of selections, but most X applications only handle one, the <I CLASS="EMPHASIS" >primary selection</I >.</P ><P >In most cases, it isn't necessary for a GTK application to deal with selections itself. The standard widgets, such as the Entry widget, already have the capability to claim the selection when appropriate (e.g., when the user drags over text), and to retrieve the contents of the selection owned by another widget or another application (e.g., when the user clicks the second mouse button). However, there may be cases in which you want to give other widgets the ability to supply the selection, or you wish to retrieve targets not supported by default.</P ><P >A fundamental concept needed to understand selection handling is that of the <I CLASS="EMPHASIS" >atom</I >. An atom is an integer that uniquely identifies a string (on a certain display). Certain atoms are predefined by the X server, and in some cases there are constants in <TT CLASS="LITERAL" >gtk.h</TT > corresponding to these atoms. For instance the constant <TT CLASS="LITERAL" >GDK_PRIMARY_SELECTION</TT > corresponds to the string "PRIMARY". In other cases, you should use the functions <TT CLASS="LITERAL" >gdk_atom_intern()</TT >, to get the atom corresponding to a string, and <TT CLASS="LITERAL" >gdk_atom_name()</TT >, to get the name of an atom. Both selections and targets are identified by atoms.</P ></DIV ></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="x1810.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="x1850.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Signal Emission and Propagation</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Retrieving the selection</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
