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<h1 align="center">Qt Tutorial 2 - Calling it Quits</h1>

<p>Files:</p>

<ul>

<li><a href="tutorial-t2-main-cpp.html">tutorial/t2/main.cpp</a></li>

</ul>

<center><img src="images/t2.png" alt="Screenshot of tutorial two" /></center><p>Having created a window in <a href="tutorial-t1.html">Chapter 1,</a> we will now go on to make the application quit properly when the user tells it to.</p>

<p>We will also use a font that is more exciting than the default one.</p>

<pre>  /****************************************************************

** Qt tutorial 2

****************************************************************/

#include <QApplication>

#include <QFont>

#include <QPushButton>

int main(int argc, char *argv[])

{

QApplication app(argc, argv);

QPushButton quit("Quit");

quit.resize(75, 30);

quit.setFont(QFont("Times", 18, QFont::Bold));

QObject::connect(&quit, SIGNAL(clicked()), &app, SLOT(quit()));

quit.show();

return app.exec();

}</pre>

<h2>Line by Line Walkthrough</h2>

<pre>  #include <QFont></pre>

<p>Since this program uses <a href="qfont.html">QFont</a>, it needs to include <tt><QFont></tt>.</p>

<pre>  QPushButton quit("Quit");</pre>

<p>This time, the button says <b>Quit</b> and that's exactly what the program will do when the user clicks the button.</p>

<pre>  quit.resize(75, 30);</pre>

<p>We've chosen another size for the button since the text is a bit shorter than "Hello world!". We could also have used <a href="qfontmetrics.html">QFontMetrics</a> to set right size, or let <a href="qpushbutton.html">QPushButton</a> choose a reasonable default.</p>

<pre>  quit.setFont(QFont("Times", 18, QFont::Bold));</pre>

<p>Here we choose a new font for the button, an 18-point bold font from the Times family. It is also possible to change the default font for the entire application, using <a href="qapplication.html#setFont">QApplication::setFont</a>().</p>

<pre>  QObject::connect(&quit, SIGNAL(clicked()), &app, SLOT(quit()));</pre>

<p><a href="qobject.html#connect">QObject::connect</a>() is perhaps <i>the</i> most central feature of Qt. Note that <a href="qobject.html#connect">connect()</a> is a static function in <a href="qobject.html">QObject</a>. Do not confuse it with the <tt>connect()</tt> function in the Berkeley socket library.</p>

<p>This <a href="qobject.html#connect">connect()</a> call establishes a one-way connection between two Qt objects (objects that inherit <a href="qobject.html">QObject</a>, directly or indirectly). Every Qt object can have both <tt>signals</tt> (to send messages) and <tt>slots</tt> (to receive messages). All widgets are Qt objects, since they inherit <a href="qwidget.html">QWidget</a>, which in turn inherits <a href="qobject.html">QObject</a>.</p>

<p>Here, the <a href="qabstractbutton.html#clicked">clicked()</a> signal of <tt>quit</tt> is connected to the <a href="qcoreapplication.html#quit">quit()</a> slot of <tt>app</tt>, so that when the button is clicked, the application quits.</p>

<p>The <a href="signalsandslots.html">Signals and Slots</a> documentation describes this topic in detail.</p>

<h2>Running the Application</h2>

<p>When you run this program, you will see an even smaller window than in Chapter 1, filled with an even smaller button.</p>

<p>See <a href="tutorial-t1.html">Chapter 1</a> for how to create a makefile and build the application.</p>

<h2>Exercises</h2>

<p>Try to resize the window. Press the button. Oops! That <a href="qobject.html#connect">connect()</a> would seem to make some difference.</p>

<p>Are there any other signals in <a href="qpushbutton.html">QPushButton</a> you can connect to quit? [Hint: The <a href="qpushbutton.html">QPushButton</a> inherits most of its functionality from <a href="qabstractbutton.html">QAbstractButton</a>.]</p>

<p>

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