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<head>
<title>Loading Documents</title>
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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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#include &lt;qtsingleapplication.h&gt;
#include &lt;QtCore/QFile&gt;
#include &lt;QtGui/QMainWindow&gt;
#include &lt;QtGui/QPrinter&gt;
#include &lt;QtGui/QPainter&gt;
#include &lt;QtGui/QTextEdit&gt;
#include &lt;QtGui/QMdiArea&gt;
#include &lt;QtCore/QTextStream&gt;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow();
public slots:
void handleMessage(const QString&amp; 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&amp; message)
{
enum Action {
Nothing,
Open,
Print
} action;
action = Nothing;
QString filename = message;
if (message.toLower().startsWith(&quot;/print &quot;)) {
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 = &quot;[[Error: Could not load file &quot; + filename + &quot;]]&quot;;
QTextEdit *view = new QTextEdit;
view-&gt;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-&gt;print(&amp;printer);
delete view;
}
break;
case Open:
{
workspace-&gt;addSubWindow(view);
view-&gt;setWindowTitle(message);
view-&gt;show();
emit needToShow();
}
break;
default:
break;
};
}</pre>
<p>Loading the file will also activate the window.</p>
<pre> #include &quot;main.moc&quot;
int main(int argc, char **argv)
{
QtSingleApplication instance(&quot;File loader QtSingleApplication example&quot;, argc, argv);
QString message;
for (int a = 1; a &lt; argc; ++a) {
message += argv[a];
if (a &lt; argc-1)
message += &quot; &quot;;
}
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(&amp;instance, SIGNAL(messageReceived(const QString&amp;)),
&amp;mw, SLOT(handleMessage(const QString&amp;)));
instance.setActivationWindow(&amp;mw, false);
QObject::connect(&amp;mw, SIGNAL(needToShow()), &amp;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&#x2e; 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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