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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><!-- /home/reggie/tmp/qt-3.0-reggie-5401/qt-x11-commercial-3.0.5/doc/actiongroup-miniwalkthrough.doc:5 --><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Walkthrough: A Tiny Editor Illustrating QActionGroup</title><style type="text/css"><!--h3.fn,span.fn { margin-left: 1cm; text-indent: -1cm; }a:link { color: #004faf; text-decoration: none }a:visited { color: #672967; text-decoration: none }body { background: #ffffff; color: black; }--></style></head><body><table border="0" cellpadding="0" cellspacing="0" width="100%"><tr bgcolor="#E5E5E5"><td valign=center> <a href="index.html"><font color="#004faf">Home</font></a> | <a href="classes.html"><font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"><font color="#004faf">Main Classes</font></a> | <a href="annotated.html"><font color="#004faf">Annotated</font></a> | <a href="groups.html"><font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"><font color="#004faf">Functions</font></a></td><td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Walkthrough: A Tiny Editor Illustrating QActionGroup</h1> <p> <p> In the following we will step through a very rudimental <a href="actiongroup-example.html">editor program</a>that shows one of the most common uses of the <a href="qactiongroup.html">QActionGroup</a> class:how to combine several toggle actions in a way that allows one-of-many choices.<p> If you're not yet familiar with the concept of <em>actions</em>,please refer to the <A HREF="simple-application-action.html">Simple ApplicationWalkthrough featuring <a href="qaction.html">QAction</a></A>.<p> <h2>A tiny main program</h2><p> <pre> #include <<a href="qapplication-h.html">qapplication.h</a>> #include "editor.h" int main( int argc, char ** argv) { <a href="qapplication.html">QApplication</a> app( argc, argv ); Editor editor; editor.<a href="qwidget.html#setCaption">setCaption</a>( "Qt Example - Actiongroup" ); app.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &editor ); editor.<a href="qwidget.html#show">show</a>(); return app.<a href="qapplication.html#exec">exec</a>(); }</pre><p> This tiny editor is a very small program. It might be unusual for an editor but it does not even provide the possibility to open a file given as a commandline argument. The reason for this is simple: It has nothing to to with QActionGroups. <p> The crucial point in the above <em>main()</em> is that we make <em>editor</em>, an objectconstructed from a self-written class <em>Editor</em>, the main widget in ourapplication. This class is defined in <em>editor.h</em>.<p> When you read through the code and happen to be unsure about something: The<A HREF="simple-application.html#simplemain">Simple Application Walkthrough</A>explains the elements of a typical Qt main program in detail.<p> <h2>The interface of the Editor class</h2><p> Before implementing the <em>Editor</em> class we should think about what itis supposed to do. Fortunately Qt provides a full-featured rich text editorclass, <a href="qtextedit.html">QTextEdit</a>. The only thing left for us is to give it a user interface.<p> <pre> #include <<a href="qmainwindow-h.html">qmainwindow.h</a>> class QTextEdit; class QAction; class Editor : public <a href="qmainwindow.html">QMainWindow</a> { <a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a> public: Editor(); private slots: void setFontColor( <a href="qaction.html">QAction</a> * ); private: <a href="qtextedit.html">QTextEdit</a> * editor; <a href="qaction.html">QAction</a> * setRedFont; };</pre><p> As we look for a means to implement one-of-many choices, a nice example wouldinvolve two buttons that make the user change the font color: If he or sheinvokes the <em>setRedFont</em> action the font color changes from default blackto red. <p> To do this color change we need a slot, <em>setFontColor()</em> that takes care about the signal the action emits.<p> The <em>Editor</em> class itself is derived from <a href="qmainwindow.html">QMainWindow</a>. Only the constructormight be called from outside the class. <p> <h2>Action!</h2><p> <p> <pre> #include "editor.h" #include <<a href="qtextedit-h.html">qtextedit.h</a>> #include <<a href="qmenubar-h.html">qmenubar.h</a>> #include <<a href="qpopupmenu-h.html">qpopupmenu.h</a>> #include <<a href="qtoolbar-h.html">qtoolbar.h</a>> #include <<a href="qaction-h.html">qaction.h</a>></pre><p> It's not that much that we need for our tiny editor: <a href="qtextedit.html">QTextEdit</a>, <a href="qmenubar.html">QMenuBar</a>,<a href="qtoolbar.html">QToolBar</a>, <a href="qpopupmenu.html">QPopupMenu</a> and last but not least <a href="qaction.html">QAction</a> and <a href="qactiongroup.html">QActionGroup</a> from <em>qaction.h</em>. <p> <pre> Editor::Editor() : <a href="qmainwindow.html">QMainWindow</a>( 0, "main window") { <a href="qactiongroup.html">QActionGroup</a> * colors = new <a href="qactiongroup.html">QActionGroup</a>( this, "colors", TRUE );</pre><p> If one of the buttons is on, the other one must be off. The easiest way toto this is to create an action group, <em>colors</em>, that controls this exclusive behaviour.This is done by setting the third argument of the QActionGroup constructor to<em>TRUE</em> (we could omit it because it's the default). As simple as this we get an <em>exclusive</em> action group that will look afterits member actions and switch off all other toggle actions except the one that is on. <p> <pre> <a href="qaction.html">QAction</a> * setBlackFont = new <a href="qaction.html">QAction</a>( "black", QPixmap( (const char**)black_xpm ), "Font color: black", CTRL+Key_B, colors, "blackfontcolor", TRUE );</pre><p> Then we create our first action, the one that sets the font color backto default black. It is called <em>setBlackFont</em> and is equipped with a descriptive <a href="qaction.html#text">QAction::text</a>() reading <em>black</em>, a <a href="qaction.html#menuText">QAction::menuText</a>() reading <em>Font color: black</em>, a <a href="qaction.html#iconSet">QAction::iconSet</a>()derived from the pixmap <em>black_xpm</em> and <em>ALT+B</em> as keyboard accelerator.<p> The last argument of the action constructor, <em>TRUE</em>, is responsible for making <em>setBlackFont</em> a toggle actionthat can be switched on or off. Most importantly <em>setBlackFont</em> becomes a memberof the <em>colors</em> action group at creation time: <em>colors</em> is defined tobe its parent.<p> <pre> setRedFont = new <a href="qaction.html">QAction</a>( "red", QPixmap( (const char**)red_xpm ), "Font color: red", CTRL+Key_R, colors, "redfontcolor", TRUE );</pre><p> The same way we create the other toggle action, <em>setRedFont</em>, as a child of <em>colors</em>.<p> Whenever one of the two members of the <em>colors</em> group emits the <a href="qaction.html#toggled">QAction::toggled</a>() signalthe <a href="qactiongroup.html">QActionGroup</a> is notified internally and emits the <a href="qactiongroup.html#selected">QActionGroup::selected</a>() signalin turn. <a href="qactiongroup.html#selected">QActionGroup::selected</a>() carries the action that caused the signal as its argument.<p> All we have to do now is to connect this signal to a slot that changesthe font color to red or black depending on the toggled action:<p> <pre> <a name="x2084"></a><a name="x2083"></a> QObject::<a href="qobject.html#connect">connect</a>( colors, SIGNAL( <a href="qactiongroup.html#selected">selected</a>( <a href="qaction.html">QAction</a> * ) ), this, SLOT( setFontColor( <a href="qaction.html">QAction</a> * ) ) );</pre><p> This is the entire trick.Thus let's recall what we have done so far: We created two toggle actions,<em>setRedFont</em> and <em>setBlackFont</em>. Because they are children of an<em>exclusive</em> QActionGroup named <em>colors</em> it is impossible for the userto type red and black at the same time: Whenever he or she invokesone of the actions the other one changes state to off, <em>colors</em>emits a <a href="qactiongroup.html#selected">QActionGroup::selected</a>() signal and the <em>setFontColor()</em> slot takes careof it.<p> All we have to do now is to add our two actions to the <em>Editor</em> window.<p> <pre> <a href="qtoolbar.html">QToolBar</a> * toolbar = new <a href="qtoolbar.html">QToolBar</a>( this, "toolbar" );</pre><p> First we create a tool bar.<p> <pre> colors-><a href="qactiongroup.html#addTo">addTo</a>( toolbar );</pre><p> But instead of adding each action manually we simply add theirparent action group to <em>toolbar</em> and are done. <em>colors</em> makes surethat <em>setBlackFont</em> and <em>setRedFont</em> find themselves presentedin the tool bar: <em>setBlackFont</em> as a tool button decorated with the <em>black_xpm</em> pixmap on the left, <em>setRedFont</em> (because it wasadded to <em>colors</em> later) to its right.<p> <pre> <a href="qpopupmenu.html">QPopupMenu</a> * font = new <a href="qpopupmenu.html">QPopupMenu</a>( this ); <a href="qmainwindow.html#menuBar">menuBar</a>()->insertItem( "&Font", font );</pre><p> Next we create a popup menu and insert it into the menu barunder the <em>Font</em> entry.<p> In a menu with this name a user would certainly expect to find morethan just two entries to change the font color. You might want toadd other font related actions in the future, and therefore it would be nice to group <em>setBlackFont</em> and <em>setRedFont</em> in a submenu entirely dedicated to the purpose of changing fontcolors.<p> With an action group this is easy. We simply tell <em>colors</em>to group together all of its members in a single submenu:<p> <pre> colors-><a href="qactiongroup.html#setUsesDropDown">setUsesDropDown</a>( TRUE );</pre><p> This however causes a problem: a submenu entry must have amenu text, and up to now we don't have any.<p> When we recall that action groups intrinsically are QActionsthemselves the solution becomes obvious:<p> <pre> colors-><a href="qaction.html#setMenuText">setMenuText</a>( "Font Color" );</pre><p> We simply assign the menu text <em>Font</em> <em>Color</em> to <em>colors</em>.<p> The rest is business as usual:<p> <pre> colors-><a href="qactiongroup.html#addTo">addTo</a>( font );</pre><p> We add the new and improved <a href="qactiongroup.html">QActionGroup</a> as a submenu tothe <em>font</em> popup menu.<p> <pre> editor = new <a href="qtextedit.html">QTextEdit</a>( this, "editor" );</pre><p> Last but not least we create the heart of <em>Editor</em>,the rich text editor ...<p> <pre> <a href="qmainwindow.html#setCentralWidget">setCentralWidget</a>( editor );</pre><p> ... and make it the central widget in our window.<p> <pre> }</pre><p> The only thing left to implement is the <em>setFontColor</em> slotthat is responsible for changing the font color to redor black depending on which action was toggled on.<p> <A NAME="setFontColor()"></A><pre> void Editor::setFontColor( <a href="qaction.html">QAction</a> * coloraction ) {</pre><p> As the <a href="qactiongroup.html#selected">QActionGroup::selected</a>() signal carries therelevant action as its argument, the first thing we have to dois to preserve it in the <em>coloraction</em> variable for later use.<p> <pre> if ( coloraction == setRedFont ) editor-><a href="qtextedit.html#setColor">setColor</a>( red );</pre><p> If <em>coloraction</em> is the same as <em>setRedFont</em> we change the <em>editor</em>'s font color to <em>red</em>.<p> <pre> else editor-><a href="qtextedit.html#setColor">setColor</a>( black );</pre><p> Otherwise it is set to <em>black</em>.<p> <pre> }</pre><p>See also <a href="step-by-step-examples.html">Step-by-step Examples</a>.<!-- eof --><p><address><hr><div align=center><table width=100% cellspacing=0 border=0><tr><td>Copyright © 2002 <a href="http://www.trolltech.com">Trolltech</a><td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a><td align=right><div align=right>Qt version 3.0.5</div></table></div></address></body></html>⌨️ 快捷键说明
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