simple-application.html

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<p>
The only thing this widget needs to do in its destructor is delete the
printer it created.  All the other objects are child widgets, which Qt
will delete as appropriate.  Simple. <pre>
    void ApplicationWindow::newDoc()
    {
        ApplicationWindow *ed = new ApplicationWindow;
        ed-&gt;<a href="qwidget.html#d6a291">setCaption</a>("Qt Example - Application");
        ed-&gt;<a href="qmainwindow.html#eb53e3">show</a>();
    }
</pre>
<p>
This slot, connected to the File->New menu item and the "new file"
tool button, simply creates a new ApplicationWindow, sets some size
and shows it. <pre>
    void ApplicationWindow::load()
    {
        <a href="qstring.html">QString</a> fn = QFileDialog::getOpenFileName( QString::null, QString::null,
                                                   this);
        if ( !fn.<a href="qstring.html#c62623">isEmpty</a>() )
            load( fn );
        else
            <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( "Loading aborted", 2000 );
    }
</pre>
<p>
This slot is connected to the "load file" menu item and tool button.
As you can see, it asks the user for a file name and then either loads
that file or gives an error message in the status bar.
<p>
(We give an error message in the status bar since that's less
bothersome.  We could have used a <a href="qmessagebox.html">QMessageBox</a>, but since we assume
the user will notice that no file was loaded, we just use the status
bar, and the user won't need to hit Enter to make some window go
away.) <pre>
    void ApplicationWindow::load( const char *fileName )
    {
        <a href="qfile.html">QFile</a> f( fileName );
        if ( !f.<a href="qfile.html#255995">open</a>( IO_ReadOnly ) )
            return;
    
        e-&gt;setAutoUpdate( FALSE );
        e-&gt;clear();
    
        <a href="qtextstream.html">QTextStream</a> t(&amp;f);
        while ( !t.<a href="qtextstream.html#bb145b">eof</a>() ) {
            <a href="qstring.html">QString</a> s = t.<a href="qtextstream.html#ae4af4">readLine</a>();
            e-&gt;append( s );
        }
        f.<a href="qfile.html#64e640">close</a>();
    
        e-&gt;setAutoUpdate( TRUE );
        e-&gt;repaint();
        e-&gt;setEdited( FALSE );
        <a href="qwidget.html#d6a291">setCaption</a>( fileName );
        <a href="qstring.html">QString</a> s;
        s.<a href="qstring.html#926f67">sprintf</a>( "Loaded document %s", fileName );
        <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( s, 2000 );
    }
</pre>
<p>
This function loads a file into the editor.  It takes care to turn off
auto-update of the editor, for faster loading and less flicker.  When
it's done, it sets the window system caption to the file name and
displays a success message for two seconds in the status bar. <pre>
    void ApplicationWindow::save()
    {
        if ( filename.isEmpty() ) {
            saveAs();
            return;
        }
    
        <a href="qstring.html">QString</a> text = e-&gt;text();
        <a href="qfile.html">QFile</a> f( filename );
        if ( !f.<a href="qfile.html#255995">open</a>( IO_WriteOnly ) ) {
            <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( <a href="qstring.html">QString</a>("Could not write to %1").arg(filename),
                                  2000 );
            return;
        }
    
        <a href="qtextstream.html">QTextStream</a> t( &amp;f );
        t &lt;&lt; text;
        f.<a href="qfile.html#64e640">close</a>();
</pre>
<p>
This function saves the current file.  Nothing remarkable in the first
part. <pre>
        e-&gt;setEdited( FALSE );
</pre>
<p>
Tell the editor that the contents haven't been edited since the last
save.  When the user closes the window, ApplicationWindow may want to
ask "Save?". <pre>
        <a href="qwidget.html#d6a291">setCaption</a>( filename );
</pre>
<p>
It may be that the document was saved under a different name than the
caption, so we set the window caption just to be sure. <pre>
        <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( <a href="qstring.html">QString</a>( "File %1 saved" ).arg( filename ), 2000 );
    }
</pre>
<p>
That was all. <pre>
    void ApplicationWindow::saveAs()
    {
        <a href="qstring.html">QString</a> fn = QFileDialog::getSaveFileName( QString::null, QString::null,
                                                   this );
        if ( !fn.<a href="qstring.html#c62623">isEmpty</a>() ) {
            filename = fn;
            save();
        } else {
            <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( "Saving aborted", 2000 );
        }
    }
</pre>
<p>
This function asks for a new name, saves the document under that name,
and implicitly changes the window system caption to the new name.
<p>
<a name="printer"></a> <pre>
    void ApplicationWindow::print()
    {
        const int Margin = 10;
        int pageNo = 1;
</pre>
<p>
print() is called by the File->Print menu item and the "print" tool
button.
<p>
Since we don't want to print to the very edges of the paper, we use a
little margin: 10 points.  And we keep track of the page count. <pre>
        if ( printer-&gt;setup(this) ) {               // printer dialog
</pre>
<p>
QPrinter::setup() invokes a print dialog, configures the printer
object, and returns TRUE if the user wants to print or FALSE if not.
So, we test the return value, and if it's TRUE, we... <pre>
            <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( "Printing..." );
</pre>
<p>
... set a status bar message in case printing takes any time. <pre>
            <a href="qpainter.html">QPainter</a> p;
            if( !p.<a href="qpainter.html#02ed5d">begin</a>( printer ) )
                return;                             // paint on printer
    
            p.<a href="qpainter.html#998df2">setFont</a>( e-&gt;font() );
            int yPos        = 0;                    // y position for each line
            <a href="qfontmetrics.html">QFontMetrics</a> fm = p.<a href="qpainter.html#73b2e5">fontMetrics</a>();
            <a href="qpaintdevicemetrics.html">QPaintDeviceMetrics</a> metrics( printer ); // need width/height
                                                    // of printer surface
</pre>
<p>
We create a painter for the output, select font, and set up some
variables we'll need. <pre>
            for( int i = 0 ; i &lt; e-&gt;numLines() ; i++ ) {
</pre>
<p>
For each line in the text editing widget, we want to print it. <pre>
                if ( Margin + yPos &gt; metrics.<a href="qpaintdevicemetrics.html#d4fedb">height</a>() - Margin ) {
</pre>
<p>
Before we print each line: Is there space for it on the current page,
given the margins we want to use?  IF not, we want to start a new
page. <pre>
                    <a href="qstring.html">QString</a> msg( "Printing (page " );
                    msg += QString::number( ++pageNo );
                    msg += ")...";
                    <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( msg );
                    printer-&gt;newPage();             // no more room on this page
                    yPos = 0;                       // back to top of page
</pre>
<p>
Four lines to tell the user what we're doing, two lines to do it. <pre>
                }
</pre>
<p>
Okay, now we know there's space for this line. <pre>
                p.<a href="qpainter.html#0f088f">drawText</a>( Margin, Margin + yPos,
                            metrics.<a href="qpaintdevicemetrics.html#95eb7b">width</a>(), fm.<a href="qfontmetrics.html#e6e380">lineSpacing</a>(),
                            ExpandTabs | DontClip,
                            e-&gt;textLine( i ) );
</pre>
<p>
Use the painter to print it.
<p>
In Qt, output to printer use the exact same code as output to screen,
pixmaps and picture metafiles.  Therefore, we don't call a QPrinter
function to draw text, we call a QPainter function.  QPainter works on
all the output devices and has a device independent API.  Most of its
code is device-independent, too, which means that it's less likely
that your application will have odd bugs.  (If the same code is used
to print as to draw on the screen, it's less likely that you'll have
printing-only or screen-only bugs.) <pre>
                yPos = yPos + fm.<a href="qfontmetrics.html#e6e380">lineSpacing</a>();
</pre>
<p>
Keep count of how much of the paper we've used. <pre>
            }
</pre>
<p>
At this point we've printed all of the text in the editing widget. <pre>
            p.<a href="qpainter.html#365784">end</a>();                                // send job to printer
            <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( "Printing completed", 2000 );
</pre>
<p>
So we tell the printer to finish off the last page and tell the user
that we're done. <pre>
        } else {
            <a href="qmainwindow.html#530937">statusBar</a>()-&gt;message( "Printing aborted", 2000 );
        }
</pre>
<p>
If the user did not want to print (and <a href="qprinter.html#c3cd23">QPrinter::setup()</a> returned
FALSE), we acknowledge that. <pre>
    }
</pre>
<p>
Tha's all.  We have printed a text document.
<p>
<a name="closeEvent"></a> <pre>
    void ApplicationWindow::closeEvent( <a href="qcloseevent.html">QCloseEvent</a>* ce )
    {
</pre>
<p>
This event get to process window-system close events.  A close event
is subtly different from a hide event: hide may often mean "iconify"
but close means that the window is going away for good. <pre>
        if ( !e-&gt;edited() ) {
            ce-&gt;<a href="qcloseevent.html#7cf66f">accept</a>();
            return;
        }
</pre>
<p>
If the text hasn't been edited, we just accept the event.  The window
will be closed, and since we used the <code>WDestructiveClose</code> widget
flag, the widget will be deleted. <pre>
        switch( <a href="qmessagebox.html#66b7c8">QMessageBox::information</a>( this, "Qt Application Example",
                                          "The document has been changed since "
                                          "the last save.",
                                          "Save Now", "Cancel", "Leave Anyway",
                                          0, 1 ) ) {
        case 0:
            save();
            ce-&gt;<a href="qcloseevent.html#7cf66f">accept</a>();
            break;
        case 1:
        default: // just for sanity
            ce-&gt;<a href="qcloseevent.html#ee1736">ignore</a>();
            break;
        case 2:
            ce-&gt;<a href="qcloseevent.html#7cf66f">accept</a>();
            break;
        }
    }
</pre>
<p>
We know the text has been edited, so we ask the user: What do you want
to do?  If the user wants to save and then exit, we do that.  If the
user wants to not exit, we ignore the close event (there is a chance
that we can't block it but we try).  If the user just wants to exit,
abandoning the edits, that's very simple. <pre>
    void ApplicationWindow::about()
    {
        <a href="qmessagebox.html#f6c3cd">QMessageBox::about</a>( this, "Qt Application Example",
                            "This example demonstrates simple use of "
                            "QMainWindow,\nQMenuBar and QToolBar.");
    }
    
    void ApplicationWindow::aboutQt()
    {
        <a href="qmessagebox.html#b72270">QMessageBox::aboutQt</a>( this, "Qt Application Example" );
    }
</pre>
<p>
These two slots use ready-made "about" functions to say a little about
this program and the GUI toolkit it uses.  (You don't need to provide
an About Qt in your programs, but if you use Qt for free we'd
appreciate it if you tell people what you're using.)
<p>
That's all.  A complete, almost useful application with nice help.
Almost as good as the "editors" some computer vendors have shipped
with their desktops.  In less than 300 lines of code.

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