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169 lines
7.6 KiB
169 lines
7.6 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:80 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Qt Tutorial - Chapter 1: Hello, World!</title>
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<style type="text/css"><!--
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fn { margin-left: 1cm; text-indent: -1cm; }
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a:link { color: #004faf; text-decoration: none }
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a:visited { color: #672967; text-decoration: none }
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body { background: #ffffff; color: black; }
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--></style>
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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| <a href="classes.html">
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<font color="#004faf">All Classes</font></a>
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| <a href="mainclasses.html">
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<font color="#004faf">Main Classes</font></a>
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| <a href="annotated.html">
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<font color="#004faf">Annotated</font></a>
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<font color="#004faf">Grouped Classes</font></a>
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| <a href="functions.html">
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<font color="#004faf">Functions</font></a>
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</td>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Qt Tutorial - Chapter 1: Hello, World!</h1>
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<p> <center><img src="t1.png" alt="Screenshot of tutorial one"></center>
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<p> This first program is a simple hello-world example. It contains only
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the bare minimum you need to get a Qt application up and running.
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The picture above is a snapshot of this program.
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<p> <pre>/****************************************************************
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**
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** Qt tutorial 1
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**
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****************************************************************/
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#include <<a href="qapplication-h.html">qapplication.h</a>>
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#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
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int main( int argc, char **argv )
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{
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<a href="qapplication.html">QApplication</a> a( argc, argv );
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<a href="qpushbutton.html">QPushButton</a> hello( "Hello world!", 0 );
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hello.<a href="qwidget.html#resize">resize</a>( 100, 30 );
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a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &hello );
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hello.<a href="qwidget.html#show">show</a>();
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return a.<a href="qapplication.html#exec">exec</a>();
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}
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</pre>
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<p> <h2> Line-by-line Walkthrough
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</h2>
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<a name="1"></a><p> <pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
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</pre>
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<p> This line includes the <a href="qapplication.html">QApplication</a> class definition. There has to be
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exactly one QApplication object in every application that uses Qt.
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QApplication manages various application-wide resources, such as the
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default font and cursor.
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<p> <pre> #include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
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</pre>
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<p> This line includes the <a href="qpushbutton.html">QPushButton</a> class definition. The
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<a href="hierarchy.html">reference documentation</a> for each class
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mentions at the top which file needs to be included to use that class.
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<p> QPushButton is a classical GUI push button that the user can press
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and release. It manages its own look and feel, like every other <a href="qwidget.html">QWidget</a>. A widget is a user interface object that can process user
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input and draw graphics. The programmer can change both the overall
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<a href="qapplication.html#setStyle">look and feel</a> and many minor
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properties of it (such as color), as well as the widget's content. A
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QPushButton can show either a text or a <a href="qpixmap.html">QPixmap</a>.
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<p> <pre> int main( int argc, char **argv )
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{
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</pre>
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<p> The main() function is the entry point to the program. Almost always
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when using Qt, main() only needs to perform some kind of initialization
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before passing the control to the Qt library, which then tells the
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program about the user's actions via events.
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<p> <tt>argc</tt> is the number of command-line arguments and <tt>argv</tt> is the
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array of command-line arguments. This is a C/C++ feature. It is not
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specific to Qt; however, Qt needs to process these arguments (see
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following).
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<p> <pre> <a href="qapplication.html">QApplication</a> a( argc, argv );
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</pre>
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<p> <tt>a</tt> is this program's <a href="qapplication.html">QApplication</a>. Here it is created and processes
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some of the command-line arguments (such as -display under X Window).
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Note that all command-line arguments recognized by Qt are removed from
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<tt>argv</tt> (and <tt>argc</tt> is decremented accordingly). See the <a href="qapplication.html#argv">QApplication::argv</a>() documentation for details.
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<p> <strong>Note:</strong> It is essential that the QApplication object be
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created before any window-system parts of Qt are used.
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<p> <pre> <a href="qpushbutton.html">QPushButton</a> hello( "Hello world!", 0 );
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</pre>
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<p> Here, <em>after</em> the QApplication, comes the first window-system code: A
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push button is created.
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<p> The button is set up to display the text "Hello world!" and be a
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window of its own (because the constructor specifies 0 for the parent
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window, inside which the button should be located).
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<p> <pre> <a name="x2285"></a> hello.<a href="qwidget.html#resize">resize</a>( 100, 30 );
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</pre>
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<p> The button is set up to be 100 pixels wide and 30 pixels high (plus the
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window system frame). In this case we don't care about the button's
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position, and we accept the default value.
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<p> <pre> <a name="x2284"></a> a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &hello );
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</pre>
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<p> The push button is chosen as the main widget for the application. If
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the user closes a main widget, the application exits.
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<p> You don't have to have a main widget, but most programs do have one.
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<p> <pre> <a name="x2286"></a> hello.<a href="qwidget.html#show">show</a>();
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</pre>
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<p> A widget is never visible when you create it. You must call show() to
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make it visible.
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<p> <pre> <a name="x2283"></a> return a.<a href="qapplication.html#exec">exec</a>();
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</pre>
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<p> This is where main() passes control to Qt, and exec() will return when
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the application exits.
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<p> In exec(), Qt receives and processes user and system events and passes
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these on to the appropriate widgets.
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<p> <pre> }
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</pre>
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<p> You should now try to compile and run this program.
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<p> <a name="compiling"></a>
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<h2> Compiling
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</h2>
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<a name="2"></a><p> To compile a C++ application you need to create a makefile. The
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easiest way to create a makefile for Qt is to use the <a href="qmake-manual.html">qmake</a> build tool supplied with Qt. If you've
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saved <tt>main.cpp</tt> in its own directory, all you have to do is:
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<pre>
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qmake -project
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qmake
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</pre>
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<p> The first command tells <a href="qmake-manual.html">qmake</a> to
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create a <tt>.pro</tt> (project) file. The second command tells it to create
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a (platform-specific) makefile based on the project file. You should
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now be able to type <tt>make</tt> (or <tt>nmake</tt> if you're using Visual
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Studio) and then run your first Qt application!
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<p> <h2> Behavior
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</h2>
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<a name="3"></a><p> When you run it, you will see a small window filled with a single
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button, and on it you can read the famous words, Hello World!
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<p> <h2> Exercises
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</h2>
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<a name="4"></a><p> Try to resize the window. Press the button. If you're running X
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Window, try running the program with the -geometry option
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(for example, <tt>-geometry 100x200+10+20</tt>).
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<p> You're now ready for <a href="tutorial1-02.html">Chapter 2.</a>
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<p> [<a href="tutorial1-02.html">Next tutorial</a>]
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[<a href="tutorial.html">Main tutorial page</a>]
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<p>
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<!-- eof -->
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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