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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Qt Toolkit - Walkthrough: A Simple Application</title><style type="text/css"><!--
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<h1 align=center> Walkthrough: A Simple Application</h1><br clear="all">
This walkthrough shows simple use of <a href="qmainwindow.html">QMainWindow</a>, <a href="qmenubar.html">QMenuBar</a>, <a href="qpopupmenu.html">QPopupMenu</a>, <a href="qtoolbar.html">QToolBar</a> and <a href="qstatusbar.html">QStatusBar</a> - the classes that every
modern application window tends to use.
<p>
It further shows some use of <a href="qwhatsthis.html">QWhatsThis</a> (for simple help) and a
typical main() using <a href="qapplication.html">QApplication</a>.
<p>
Finally, it shows a typical printout function that uses <a href="qprinter.html">QPrinter</a>.
<p>
<h2>The declaration of ApplicationWindow</h2
<p>
Here's the header file in full: <pre>/****************************************************************************
** $Id: qt/examples/application/application.h 2.3.2 edited 2001-01-26 $
**
** Copyright (C) 1992-2000 Trolltech AS. All rights reserved.
**
** This file is part of an example program for Qt. This example
** program may be used, distributed and modified without limitation.
**
*****************************************************************************/
#ifndef APPLICATION_H
#define APPLICATION_H
#include <<a href="qmainwindow-h.html">qmainwindow.h</a>>
class QMultiLineEdit;
class QToolBar;
class QPopupMenu;
class ApplicationWindow: public QMainWindow
{
Q_OBJECT
public:
ApplicationWindow();
~ApplicationWindow();
protected:
void closeEvent( <a href="qcloseevent.html">QCloseEvent</a>* );
private slots:
void newDoc();
void load();
void load( const char *fileName );
void save();
void saveAs();
void print();
void about();
void aboutQt();
private:
<a href="qprinter.html">QPrinter</a> *printer;
<a href="qmultilineedit.html">QMultiLineEdit</a> *e;
<a href="qtoolbar.html">QToolBar</a> *fileTools;
<a href="qstring.html">QString</a> filename;
};
#endif
</pre>
<p>
There's nothing much particular about this. It declares a class that
inherits QMainWindow, with some slots and some private variables. And
it uses a class predeclarations to speed up compiles: <code>QMultiLineEdit,</code> <code>QToolBar</code> and <code>QPopupMenu</code> are declared, not
included. make depend then won't think that every .cpp file that
includes application.h needs to be recompiled when e.g. qpopupmenu.h
changes.
<p>
<a href="simplemain"></a>
<h2>The simple main()</h2
<p>
Here's examples/main.cpp, in full. <pre>/****************************************************************************
** $Id: qt/examples/application/main.cpp 2.3.2 edited 2001-06-12 $
**
** Copyright (C) 1992-2000 Trolltech AS. All rights reserved.
**
** This file is part of an example program for Qt. This example
** program may be used, distributed and modified without limitation.
**
*****************************************************************************/
#include <<a href="qapplication-h.html">qapplication.h</a>>
#include "application.h"
int main( int argc, char ** argv ) {
<a href="qapplication.html">QApplication</a> a( argc, argv );
ApplicationWindow * mw = new ApplicationWindow();
mw-><a href="qwidget.html#d6a291">setCaption</a>( "Qt Example - Application" );
mw-><a href="qmainwindow.html#eb53e3">show</a>();
a.<a href="qobject.html#7f8e37">connect</a>( &a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()) );
return a.<a href="qapplication.html#84c7bf">exec</a>();
}
</pre>
<p>
We'll go over main() in detail. <pre>
int main( int argc, char ** argv ) {
<a href="qapplication.html">QApplication</a> a( argc, argv );
</pre>
<p>
We create a QApplication object with the usual constructor and let it
parse <em>argc</em> and <em>argv</em> so that on X11, this program behaves as X
programs are expected to. <pre>
ApplicationWindow * mw = new ApplicationWindow();
mw-><a href="qwidget.html#d6a291">setCaption</a>( "Qt Example - Application" );
mw-><a href="qmainwindow.html#eb53e3">show</a>();
</pre>
<p>
We create an ApplicationWindow as a top-level widget, set its window
system caption to "Document 1", and show() it.
<p>
<a name="close"></a> <pre>
a.<a href="qobject.html#7f8e37">connect</a>( &a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()) );
</pre>
<p>
When the application's last window is closed, it should quit. <pre>
return a.<a href="qapplication.html#84c7bf">exec</a>();
</pre>
<p>
Having completed the application initialization, we start the main
event loop (the GUI), and eventually return the error code
QApplication returns when it leaves the event loop.
(<a href="qapplication.html#7328f6">QApplication::exit()</a> lets any part of the program set this code in
a way that doesn't prohibit an orderly closedown.) <pre>
}
</pre>
<p>
<h2>The implementation of ApplicationWindow</h2>
<p>
Since the implementation is much larger (almost 200 lines) we won't
include it in full but instead include bits and pieces as necessary.
We skip the preliminary #include and some text constants, and start
with the constructor. <pre>
ApplicationWindow::ApplicationWindow()
: <a href="qmainwindow.html">QMainWindow</a>( 0, "example application main window", WDestructiveClose )
{
</pre>
<p>
ApplicationWindow inherits QMainWindow, the Qt class that provides
typical application main windows, with menu bars, tool bars, etc. <pre>
int id;
printer = new <a href="qprinter.html">QPrinter</a>;
</pre>
<p>
The application example can print things, and we chose to have a
QPrinter object lying around so that when the user changes a setting
during one printing, the new setting will be the default next time. <pre>
<a href="qpixmap.html">QPixmap</a> openIcon, saveIcon, printIcon;
</pre>
<p>
This example is simple enough to have just three commands. These
variables are used to hold the icons for each of them. <pre>
fileTools = new <a href="qtoolbar.html">QToolBar</a>( this, "file operations" );
</pre>
<p>
We create a tool bar in <em>this</em> window for putting some tools in. <pre>
fileTools->setLabel( <a href="qobject.html#2418a9">tr</a>( "File Operations" ) );
openIcon = QPixmap( fileopen );
<a href="qtoolbutton.html">QToolButton</a> * fileOpen
= new <a href="qtoolbutton.html">QToolButton</a>( openIcon, "Open File", QString::null,
this, SLOT(load()), fileTools, "open file" );
saveIcon = QPixmap( filesave );
<a href="qtoolbutton.html">QToolButton</a> * fileSave
= new <a href="qtoolbutton.html">QToolButton</a>( saveIcon, "Save File", QString::null,
this, SLOT(save()), fileTools, "save file" );
printIcon = QPixmap( fileprint );
<a href="qtoolbutton.html">QToolButton</a> * filePrint
= new <a href="qtoolbutton.html">QToolButton</a>( printIcon, "Print File", QString::null,
this, SLOT(print()), fileTools, "print file" );
</pre>
<p>
And then we create three tool buttons in that tool bar, each with the
appropriate icons and tool-tip text. The three buttons are connected
to slots in this object, for example the "Print File" button is
connected to ApplicationWindow::print(). <pre>
(void)QWhatsThis::whatsThisButton( fileTools );
</pre>
<p>
Then we create a fourth button in the toolbar: A special button that
provides "What's This?" help. This must be set up using a special
function, as its mouse interface needs to be a little unusual. <pre>
<a href="qwhatsthis.html#dfcd18">QWhatsThis::add</a>( fileOpen, fileOpenText );
<a href="qmimesourcefactory.html#5c7072">QMimeSourceFactory::defaultFactory</a>()->setPixmap( "fileopen", openIcon );
<a href="qwhatsthis.html#dfcd18">QWhatsThis::add</a>( fileSave, fileSaveText );
<a href="qwhatsthis.html#dfcd18">QWhatsThis::add</a>( filePrint, filePrintText );
</pre>
<p>
We add What's This? help for each of the three buttons, and tell the
QML engine that when a help text wants the "fileopen" image, it should
use the pixmap we've defined. <pre>
<a href="qpopupmenu.html">QPopupMenu</a> * file = new <a href="qpopupmenu.html">QPopupMenu</a>( this );
<a href="qmainwindow.html#0eb7bc">menuBar</a>()->insertItem( "&File", file );
file-><a href="qmenudata.html#0076cb">insertItem</a>( "&New", this, SLOT(newDoc()), CTRL+Key_N );
id = file-><a href="qmenudata.html#0076cb">insertItem</a>( openIcon, "&Open",
this, SLOT(load()), CTRL+Key_O );
file-><a href="qmenudata.html#88eb55">setWhatsThis</a>( id, fileOpenText );
id = file-><a href="qmenudata.html#0076cb">insertItem</a>( saveIcon, "&Save",
this, SLOT(save()), CTRL+Key_S );
file-><a href="qmenudata.html#88eb55">setWhatsThis</a>( id, fileSaveText );
id = file-><a href="qmenudata.html#0076cb">insertItem</a>( "Save &as...", this, SLOT(saveAs()) );
file-><a href="qmenudata.html#88eb55">setWhatsThis</a>( id, fileSaveText );
file-><a href="qmenudata.html#e34b79">insertSeparator</a>();
id = file-><a href="qmenudata.html#0076cb">insertItem</a>( printIcon, "&Print",
this, SLOT(print()), CTRL+Key_P );
file-><a href="qmenudata.html#88eb55">setWhatsThis</a>( id, filePrintText );
file-><a href="qmenudata.html#e34b79">insertSeparator</a>();
file-><a href="qmenudata.html#0076cb">insertItem</a>( "&Close", this, SLOT(<a href="qwidget.html#3d9c87">close</a>()), CTRL+Key_W );
file-><a href="qmenudata.html#0076cb">insertItem</a>( "&Quit", qApp, SLOT( closeAllWindows() ), CTRL+Key_Q );
</pre>
<p>
We create a QPopupMenu item for the File menu, add it to the menu bar,
populate it with three commands, and set What's This? help for them.
<p>
Note in particular how What's This? help and pixmaps are used in both
the toolbar (above) and the menu bar (here). <pre>
<a href="qpopupmenu.html">QPopupMenu</a> * help = new <a href="qpopupmenu.html">QPopupMenu</a>( this );
<a href="qmainwindow.html#0eb7bc">menuBar</a>()->insertSeparator();
<a href="qmainwindow.html#0eb7bc">menuBar</a>()->insertItem( "&Help", help );
help-><a href="qmenudata.html#0076cb">insertItem</a>( "&About", this, SLOT(about()), Key_F1 );
help-><a href="qmenudata.html#0076cb">insertItem</a>( "About &<a href="qt.html">Qt</a>", this, SLOT(aboutQt()) );
help-><a href="qmenudata.html#e34b79">insertSeparator</a>();
help-><a href="qmenudata.html#0076cb">insertItem</a>( "What's &This", this, SLOT(<a href="qmainwindow.html#f50ce2">whatsThis</a>()), SHIFT+Key_F1 );
</pre>
<p>
We create a Help menu, add it to the menu bar, and insert a few
commands in the Help menu. <pre>
e = new <a href="qmultilineedit.html">QMultiLineEdit</a>( this, "editor" );
e->setFocus();
<a href="qmainwindow.html#fce9ba">setCentralWidget</a>( e );
</pre>
<p>
We create a multi-line edit widget, set the initial focus to be there,
and make it the central widget of this window.
<p>
QMainWindow::centralWidget() is the meat: It's what the menu bar,
status bar and tool bars are all arranged around. Since this
application is an editor, the central widget is a text editing widget
:) <pre>
<a href="qmainwindow.html#530937">statusBar</a>()->message( "Ready", 2000 );
</pre>
<p>
We make the status bar say "Ready" for two seconds at startup, just to
tell the user that this window has finished initialization and can be
used. <pre>
<a href="qwidget.html#ff9d07">resize</a>( 450, 600 );
</pre>
<p>
We provide a nice default size for the new window. <pre>
}
</pre>
<p>
That's it. <pre>
ApplicationWindow::~ApplicationWindow()
{
delete printer;
}
</pre>
<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-><a href="qwidget.html#d6a291">setCaption</a>("Qt Example - Application");
ed-><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>()->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->setAutoUpdate( FALSE );
e->clear();
<a href="qtextstream.html">QTextStream</a> t(&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->append( s );
}
f.<a href="qfile.html#64e640">close</a>();
e->setAutoUpdate( TRUE );
e->repaint();
e->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>()->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->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>()->message( <a href="qstring.html">QString</a>("Could not write to %1").arg(filename),
2000 );
return;
}
<a href="qtextstream.html">QTextStream</a> t( &f );
t << 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->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>()->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>()->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->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>()->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->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 < e->numLines() ; i++ ) {
</pre>
<p>
For each line in the text editing widget, we want to print it. <pre>
if ( Margin + yPos > 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>()->message( msg );
printer->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->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>()->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>()->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->edited() ) {
ce-><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-><a href="qcloseevent.html#7cf66f">accept</a>();
break;
case 1:
default: // just for sanity
ce-><a href="qcloseevent.html#ee1736">ignore</a>();
break;
case 2:
ce-><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.
<p><address><hr><div align="center">
<table width="100%" cellspacing="0" border="0"><tr>
<td>Copyright 2001 Trolltech<td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a>
<td align="right"><div align="right">Qt version 2.3.2</div>
</table></div></address></body></html>
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