simple-application-action.html
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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/application-action-walkthrough.doc:5 --><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Walkthrough: A Simple Application with Actions</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 Simple Application with Actions</h1> <p> <p> While reading through the implementation of the <A HREF="simple-application.html#ApplicationWindow"><em>ApplicationWindow</em> constructor</A> you have maybe asked yourself: "The <em>fileOpen</em> tool-buttonin the toolbar does exactly the same thing as the <em>File->Open</em> menu-entry.Their "What's this?" help is the same, the icons common, the sameslot is connected to both them ...Shouldn't it be possible to save some code and don't inventthe wheel twice?"<p> Indeed, it is. In modern GUI-application programming you will useso called <em>actions</em> to do this. An action collects all thecommon items (icon, tooltip, menu-entry text, shortcuts, "What's this?" help-textand what to do -- the actual action) together. Whenever this action is required(in the toolbar, as a menu-entry) all the programmer has to do isto insert the action in the respective toolbar or menu. Its appearance (as a tool-button or a menu-entry) is something, theprogrammer does not has to worry about -- it's obvious from the context.<p> With the <a href="qaction.html">QAction</a> class, Qt provides you with everything you need to use this striking concept. So let's write an <em>ApplicationWindow</em> constructor that makes use of actions.<p> <h2>The ApplicationWindow constructor with Actions</h2><p> <p> <a name="ApplicationWindow"></a><pre> ApplicationWindow::ApplicationWindow() : <a href="qmainwindow.html">QMainWindow</a>( 0, "example application main window", WDestructiveClose ) { printer = new <a href="qprinter.html">QPrinter</a>;</pre><p> Nothing new so far. But with the next lines...<p> <pre> <a href="qaction.html">QAction</a> * fileNewAction; <a href="qaction.html">QAction</a> * fileOpenAction; <a href="qaction.html">QAction</a> * fileSaveAction, * fileSaveAsAction, * filePrintAction; <a href="qaction.html">QAction</a> * fileCloseAction, * fileQuitAction;</pre><p> ... the difference becomes obvious. Here we define the actions our applicationis supposed to undertake: it should create a new editor-instance (<em>fileNewAction</em>),open a file, save a file, save it under a different name, print thecontent of the editor, close an editor window and quit the entire application.<p> <pre> fileNewAction = new <a href="qaction.html">QAction</a>( "New", "&New", CTRL+Key_N, this, "new" );</pre><p> The first one has the name <em>new</em> and can be reached via the accelerator <em>Ctrl+N</em>.When used as a menu-entry it will provide the entry <em>New</em> and can be reached via the accelerator <em>Alt-N</em> (<em>&N</em>). As we won't set a special tooltip-text, thetext <em>New</em> with the accelerator <em>Ctrl+N</em> in brackets will show up whena user holds the mouse over a tool-button and does nothing.<p> <pre> <a href="qobject.html#connect">connect</a>( fileNewAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , this, SLOT( newDoc() ) );</pre><p> When the action becomes activated (the user chooses the respective menu-entry or clicks an appropriate tool-button), it connects to the<A HREF="simple-application.html#newDoc()"><em>newDoc()</A></em> slot. <p> <pre> fileOpenAction = new <a href="qaction.html">QAction</a>( "Open File", QPixmap( fileopen ), "&Open", CTRL+Key_O, this, "open" ); <a href="qobject.html#connect">connect</a>( fileOpenAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , this, SLOT( choose() ) );</pre><p> The same way we create an <em>Open</em> <em>File</em> action and connect its <em>activated()</em> signalto the <A HREF="simple-application.html#choose()"><em>choose()</A></em> slot.There is however a novelty: the <em>fileOpenAction</em> (unlike <em>fileNewAction</em>)is assigned a pixmap (the one included with the <em>fileopen.xpm</em> file). <p> <pre> const char * fileOpenText = "<p><img source=\"fileopen\"> " "Click this button to open a <em>new file</em>. <br>" "You can also select the <b>Open</b> command " "from the <b>File</b> menu.</p>";</pre><p> For the <em>fileOpenAction</em> we want to provide "What's This?" help and thereforedefine an appropriate rich-text. <p> <pre> <a name="x2072"></a> QMimeSourceFactory::<a href="qmimesourcefactory.html#defaultFactory">defaultFactory</a>()->setPixmap( "fileopen", <a name="x2070"></a> fileOpenAction-><a href="qaction.html#iconSet">iconSet</a>().pixmap() );</pre><p> As <em>fileOpenText</em> makes use of a pixmap, we have to inform the rich-textengine that it should provide the pixmap defined for <em>fileOpenAction</em> whenever a rich-textasks for an image-source named <em>fileopen</em>.<p> The slightly complex procedure to gain the pixmap from the action isdue to the fact that a <a href="qaction.html">QAction</a> is not simply assigned a pixmap but anentire iconset. A <a href="qiconset.html">QIconSet</a> provides up to six pixmaps suited fordifferent sizes (large, small) and modes (active, disabled etc.).As we initially fed <em>fileOpenAction</em> with just one pixmap its iconsetwill be calculated from it automatically. <p> For simplicity reasons we want the icon in the "What's this?" text to be the same we used in the <em>fileOpenAction</em> constructor. This is done by using<a href="qiconset.html#pixmap">QIconSet::pixmap</a>() upon <em>fileOpenAction</em>'s <em>iconSet()</em>.<p> <pre> <a name="x2071"></a> fileOpenAction-><a href="qaction.html#setWhatsThis">setWhatsThis</a>( fileOpenText );</pre><p> Finally we assign "What's this?" help to the <em>fileOpenAction</em>.<p> <pre> fileSaveAction = new <a href="qaction.html">QAction</a>( "Save File", QPixmap( filesave ), "&Save", CTRL+Key_S, this, "save" ); <a href="qobject.html#connect">connect</a>( fileSaveAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , this, SLOT( save() ) ); const char * fileSaveText = "<p>Click this button to save the file you " "are editing. You will be prompted for a file name.\n" "You can also select the <b>Save</b> command " "from the <b>File</b> menu.</p>"; fileSaveAction-><a href="qaction.html#setWhatsThis">setWhatsThis</a>( fileSaveText );</pre><p> The same way we create a <em>Save</em> <em>File</em> action with a pixmap, "What's this?" helpand the more common items like menu-entry text and accelerator. Notethat we don't have to bother with the rich-text engine because thepixmap is not used in <em>fileSaveText</em>. When activatedthe <em>fileSaveAction</em> will call the <A HREF="simple-application.html#save()"><em>save()</A></em> slot. <p> <pre> fileSaveAsAction = new <a href="qaction.html">QAction</a>( "Save File As", "Save &as", 0, this, "save as" ); <a href="qobject.html#connect">connect</a>( fileSaveAsAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , this, SLOT( saveAs() ) ); fileSaveAsAction-><a href="qaction.html#setWhatsThis">setWhatsThis</a>( fileSaveText );</pre><p> For the <em>Save</em> <em>File</em> <em>As</em> action we reuse <em>fileSaveText</em> but do without apixmap. On activation, this action calls the <A HREF="simple-application.html#saveAs()"><em>saveAs()</A></em> slot. <p> <pre> filePrintAction = new <a href="qaction.html">QAction</a>( "Print File", QPixmap( fileprint ), "&Print", CTRL+Key_P, this, "print" ); <a href="qobject.html#connect">connect</a>( filePrintAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , this, SLOT( print() ) ); const char * filePrintText = "Click this button to print the file you " "are editing.\n You can also select the Print " "command from the File menu."; filePrintAction-><a href="qaction.html#setWhatsThis">setWhatsThis</a>( filePrintText );</pre><p> The <em>Print</em> <em>File</em> action -- with an <em>activated()</em> signal connected to <A HREF="simple-application.html#printer"><em>print()</A></em> -- looks very muchlike <em>fileSaveText</em>.<p> <pre> fileCloseAction = new <a href="qaction.html">QAction</a>( "Close", "&Close", CTRL+Key_W, this, "close" ); <a href="qobject.html#connect">connect</a>( fileCloseAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , this, SLOT( <a href="qwidget.html#close">close</a>() ) ); fileQuitAction = new <a href="qaction.html">QAction</a>( "Quit", "&Quit", CTRL+Key_Q, this, "quit" ); <a href="qobject.html#connect">connect</a>( fileQuitAction, SIGNAL( <a href="qaction.html#activated">activated</a>() ) , qApp, SLOT( <a href="qapplication.html#closeAllWindows">closeAllWindows</a>() ) );</pre><p> For the last two actions, <em>fileCloseAction</em> and <em>fileQuitAction</em>, we do it theeasy way: no "What's this?", no pixmaps. Thus we have defined all theactions we need.<p> The only thing left is to use them as menu- and toolbar-entries. <p> <pre> // populate a tool bar with some actions <a href="qtoolbar.html">QToolBar</a> * fileTools = new <a href="qtoolbar.html">QToolBar</a>( this, "file operations" ); fileTools-><a href="qtoolbar.html#setLabel">setLabel</a>( "File Operations" );</pre><p> First we create a toolbar in <em>this</em> windowand define a caption for it. <p> As actions that weren't assigned a pixmap are quite useless in a toolbarwe'll restrict ourselves to three tool-buttons for opening, saving and printing files.<p> <pre> fileOpenAction-><a href="qaction.html#addTo">addTo</a>( fileTools );</pre><p> The first tool-button is easily installed: All we have to do is to add the <em>fileOpenAction</em> to the <em>fileTools</em> toolbar.<p> <pre> fileSaveAction-><a href="qaction.html#addTo">addTo</a>( fileTools ); filePrintAction-><a href="qaction.html#addTo">addTo</a>( fileTools );</pre><p> The same easy procedure applies to <em>fileSaveAction</em> and <em>filePrintAction</em>.<p> <pre> (void)QWhatsThis::whatsThisButton( fileTools );</pre><p> To provide the user with a means to toggle his or her mouse in "What's this?" mode,we need a fourth icon in the toolbar: the (predefined) "What's this?" button.<p> <pre> // populate a menu with all actions <a href="qpopupmenu.html">QPopupMenu</a> * file = new <a href="qpopupmenu.html">QPopupMenu</a>( this ); <a href="qmainwindow.html#menuBar">menuBar</a>()->insertItem( "&File", file );</pre><p> Next we install the newly created <em>file</em> popup-menu in the menu bar.After we're done with this, we populate the menu ...<p> <pre> fileNewAction-><a href="qaction.html#addTo">addTo</a>( file ); fileOpenAction-><a href="qaction.html#addTo">addTo</a>( file ); fileSaveAction-><a href="qaction.html#addTo">addTo</a>( file ); fileSaveAsAction-><a href="qaction.html#addTo">addTo</a>( file );</pre><p> ... with some menu-entries derived from actions, ...<p> <pre> file-><a href="qmenudata.html#insertSeparator">insertSeparator</a>();</pre><p> ... a separator ...<p> <pre> filePrintAction-><a href="qaction.html#addTo">addTo</a>( file ); file-><a href="qmenudata.html#insertSeparator">insertSeparator</a>(); fileCloseAction-><a href="qaction.html#addTo">addTo</a>( file ); fileQuitAction-><a href="qaction.html#addTo">addTo</a>( file );</pre><p> ... and more actions and separators.<p> The rest of the constructor ...<p> <pre> <a href="qmainwindow.html#menuBar">menuBar</a>()->insertSeparator(); // add a help menu <a href="qpopupmenu.html">QPopupMenu</a> * help = new <a href="qpopupmenu.html">QPopupMenu</a>( this ); <a href="qmainwindow.html#menuBar">menuBar</a>()->insertItem( "&Help", help ); help-><a href="qmenudata.html#insertItem">insertItem</a>( "&About", this, SLOT(about()), Key_F1 ); help-><a href="qmenudata.html#insertItem">insertItem</a>( "About &Qt", this, SLOT(aboutQt()) ); help-><a href="qmenudata.html#insertSeparator">insertSeparator</a>(); help-><a href="qmenudata.html#insertItem">insertItem</a>( "What's &This", this, SLOT(<a href="qmainwindow.html#whatsThis">whatsThis</a>()), SHIFT+Key_F1 ); // create and define the central widget e = new <a href="qtextedit.html">QTextEdit</a>( this, "editor" ); e-><a href="qwidget.html#setFocus">setFocus</a>(); <a href="qmainwindow.html#setCentralWidget">setCentralWidget</a>( e ); <a href="qmainwindow.html#statusBar">statusBar</a>()->message( "Ready", 2000 ); <a href="qwidget.html#resize">resize</a>( 450, 600 ); }</pre><p> ... is exactly the same as in the <A HREF="simple-application.html#common_constructor">tool-button and menu-entry version</A>.<p> <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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