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</tr></table><h1 class="title">Loading Documents<br /><span class="subtitle"></span>
</h1>
<p>The application in this example loads or prints the documents passed as commandline parameters to further instances of this application.</p>
<pre><span class="comment"> /****************************************************************************
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** This file is part of the Qt Solutions component.
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** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
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** notice, this list of conditions and the following disclaimer.
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#include <qtsingleapplication.h>
#include <QtCore/QFile>
#include <QtGui/QMainWindow>
#include <QtGui/QPrinter>
#include <QtGui/QPainter>
#include <QtGui/QTextEdit>
#include <QtGui/QMdiArea>
#include <QtCore/QTextStream>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow();
public slots:
void handleMessage(const QString& message);
signals:
void needToShow();
private:
QMdiArea *workspace;
};</pre>
<p>The user interface in this application is a <a href="http://qt.nokia.com/doc/4.6/qmainwindow.html">QMainWindow</a> subclass with a <a href="http://qt.nokia.com/doc/4.6/qmdiarea.html">QMdiArea</a> as the central widget. It implements a slot <tt>handleMessage()</tt> that will be connected to the messageReceived() signal of the <a href="qtsingleapplication.html">QtSingleApplication</a> class.</p>
<pre> MainWindow::MainWindow()
{
workspace = new QMdiArea(this);
setCentralWidget(workspace);
}</pre>
<p>The <a href="http://qt.nokia.com/doc/4.6/designer-to-know.html">MainWindow</a> constructor creates a minimal user interface.</p>
<pre> void MainWindow::handleMessage(const QString& message)
{
enum Action {
Nothing,
Open,
Print
} action;
action = Nothing;
QString filename = message;
if (message.toLower().startsWith("/print ")) {
filename = filename.mid(7);
action = Print;
} else if (!message.isEmpty()) {
action = Open;
}
if (action == Nothing) {
emit needToShow();
return;
}
QFile file(filename);
QString contents;
if (file.open(QIODevice::ReadOnly))
contents = file.readAll();
else
contents = "[[Error: Could not load file " + filename + "]]";
QTextEdit *view = new QTextEdit;
view->setPlainText(contents);
switch(action) {</pre>
<p>The handleMessage() slot interprets the message passed in as a filename that can be prepended with <i>/print</i> to indicate that the file should just be printed rather than loaded.</p>
<pre> case Print:
{
QPrinter printer;
view->print(&printer);
delete view;
}
break;
case Open:
{
workspace->addSubWindow(view);
view->setWindowTitle(message);
view->show();
emit needToShow();
}
break;
default:
break;
};
}</pre>
<p>Loading the file will also activate the window.</p>
<pre> #include "main.moc"
int main(int argc, char **argv)
{
QtSingleApplication instance("File loader QtSingleApplication example", argc, argv);
QString message;
for (int a = 1; a < argc; ++a) {
message += argv[a];
if (a < argc-1)
message += " ";
}
if (instance.sendMessage(message))
return 0;</pre>
<p>The <tt>main</tt> entry point function creates a <a href="qtsingleapplication.html">QtSingleApplication</a> object, and creates a message to send to a running instance of the application. If the message was sent successfully the process exits immediately.</p>
<pre> MainWindow mw;
mw.handleMessage(message);
mw.show();
QObject::connect(&instance, SIGNAL(messageReceived(const QString&)),
&mw, SLOT(handleMessage(const QString&)));
instance.setActivationWindow(&mw, false);
QObject::connect(&mw, SIGNAL(needToShow()), &instance, SLOT(activateWindow()));
return instance.exec();
}</pre>
<p>If the message could not be sent the application starts up. Note that <tt>false</tt> is passed to the call to setActivationWindow() to prevent automatic activation for every message received, e.g. when the application should just print a file. Instead, the message handling function determines whether activation is requested, and signals that by emitting the needToShow() signal. This is then simply connected directly to <a href="qtsingleapplication.html">QtSingleApplication</a>'s activateWindow() slot.</p>
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