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| author | Timothy Pearson <kb9vqf@pearsoncomputing.net> | 2011-07-10 15:24:15 -0500 |
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| committer | Timothy Pearson <kb9vqf@pearsoncomputing.net> | 2011-07-10 15:24:15 -0500 |
| commit | bd0f3345a938b35ce6a12f6150373b0955b8dd12 (patch) | |
| tree | 7a520322212d48ebcb9fbe1087e7fca28b76185c /doc/html/tutorial1-04.html | |
| download | qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.tar.gz qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.zip | |
Add Qt3 development HEAD version
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diff --git a/doc/html/tutorial1-04.html b/doc/html/tutorial1-04.html new file mode 100644 index 0000000..524ce69 --- /dev/null +++ b/doc/html/tutorial1-04.html @@ -0,0 +1,182 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:378 --> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>Qt Tutorial - Chapter 4: Let There Be Widgets</title> +<style type="text/css"><!-- +fn { margin-left: 1cm; text-indent: -1cm; } +a:link { color: #004faf; text-decoration: none } +a:visited { color: #672967; text-decoration: none } +body { background: #ffffff; color: black; } +--></style> +</head> +<body> + +<table border="0" cellpadding="0" cellspacing="0" width="100%"> +<tr bgcolor="#E5E5E5"> +<td valign=center> + <a href="index.html"> +<font color="#004faf">Home</font></a> + | <a href="classes.html"> +<font color="#004faf">All Classes</font></a> + | <a href="mainclasses.html"> +<font color="#004faf">Main Classes</font></a> + | <a href="annotated.html"> +<font color="#004faf">Annotated</font></a> + | <a href="groups.html"> +<font color="#004faf">Grouped Classes</font></a> + | <a href="functions.html"> +<font color="#004faf">Functions</font></a> +</td> +<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 4: Let There Be Widgets</h1> + + +<p> <center><img src="t4.png" alt="Screenshot of tutorial four"></center> +<p> This example shows how to create your own widget, describes how to control the +minimum and maximum sizes of a widget, and introduces widget names. +<p> <pre>/**************************************************************** +** +** Qt tutorial 4 +** +****************************************************************/ + +#include <<a href="qapplication-h.html">qapplication.h</a>> +#include <<a href="qpushbutton-h.html">qpushbutton.h</a>> +#include <<a href="qfont-h.html">qfont.h</a>> + + +class MyWidget : public <a href="qwidget.html">QWidget</a> +{ +public: + MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 ); +}; + + +<a name="f552"></a>MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name ) + : <a href="qwidget.html">QWidget</a>( parent, name ) +{ + <a href="qwidget.html#setMinimumSize">setMinimumSize</a>( 200, 120 ); + <a href="qwidget.html#setMaximumSize">setMaximumSize</a>( 200, 120 ); + + <a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" ); + quit-><a href="qwidget.html#setGeometry">setGeometry</a>( 62, 40, 75, 30 ); + quit-><a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) ); + + <a href="qobject.html#connect">connect</a>( quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), qApp, SLOT(<a href="qapplication.html#quit">quit</a>()) ); +} + + +int main( int argc, char **argv ) +{ + <a href="qapplication.html">QApplication</a> a( argc, argv ); + + MyWidget w; + w.<a href="qwidget.html#setGeometry">setGeometry</a>( 100, 100, 200, 120 ); + a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &w ); + w.<a href="qwidget.html#show">show</a>(); + return a.<a href="qapplication.html#exec">exec</a>(); +} +</pre> + + + +<p> <h2> Line-by-line Walkthrough +</h2> +<a name="1"></a><p> <pre> class MyWidget : public <a href="qwidget.html">QWidget</a> + { + public: + MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 ); + }; +</pre> +<p> Here we create a new class. Because this class inherits from <a href="qwidget.html">QWidget</a>, +the new class is a widget and may be a top level window or a child +widget (like the push button in Chapter 3). +<p> This class has only one member, a constructor (in addition to the +members it inherits from QWidget). The constructor is a standard Qt +widget constructor; you should always include a similar constructor +when you create widgets. +<p> The first argument is its parent widget. To create a top-level window +you specify a null pointer as the parent. As you can see, this widget +defaults to be a top-level window. +<p> The second argument is the widget's name. This is <em>not</em> the text +that appears in the window's title bar or in the button. It is a name +associated with a widget to make it possible to <a href="qobject.html#queryList">look up</a> this widget later, and there is +also a <a href="qobject.html#dumpObjectTree">handy debugging function</a> that will list a complete widget hierarchy. +<p> <pre> MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name ) + : <a href="qwidget.html">QWidget</a>( parent, name ) +</pre> +<p> The implementation of the constructor starts here. Like most widgets, +it just passes on the <tt>parent</tt> and <tt>name</tt> to the <a href="qwidget.html">QWidget</a> +constructor. +<p> <pre> { + <a href="qwidget.html#setMinimumSize">setMinimumSize</a>( 200, 120 ); + <a href="qwidget.html#setMaximumSize">setMaximumSize</a>( 200, 120 ); +</pre> +<p> Because this widget doesn't know how to handle resizing, we fix its size +by setting the minimum and maximum to be equal. In the next chapter +we will show how a widget can respond to resize event from the user. +<p> <pre> <a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" ); + <a name="x2308"></a> quit-><a href="qwidget.html#setGeometry">setGeometry</a>( 62, 40, 75, 30 ); + <a name="x2307"></a> quit-><a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) ); +</pre> +<p> Here we create and set up a child widget of this widget (the new widget's +parent is <tt>this</tt>) which has the widget name "quit". The widget +name has nothing to do with the button text; it just happens to be +similar in this case. +<p> Note that <tt>quit</tt> is a local variable in the constructor. MyWidget +does not keep track of it, but Qt does, and will by default delete it +when MyWidget is deleted. This is why MyWidget doesn't need a +destructor. (On the other hand, there is no harm in deleting a child +when you choose to, the child will automatically tell Qt about its +imminent death.) +<p> The setGeometry() call does the same as move() and resize() did in the +previous chapters. +<p> <pre> <a name="x2306"></a><a name="x2304"></a> <a href="qobject.html#connect">connect</a>( quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), qApp, SLOT(<a href="qapplication.html#quit">quit</a>()) ); + } +</pre> +<p> Because the MyWidget class doesn't know about the application object, it +has to connect to Qt's pointer to it, <tt>qApp</tt>. +<p> A widget is a software component and should know as little as possible +about its environment in order to be as general and reusable as +possible. +<p> Knowing the name of the application object would break this principle, +so Qt offers an alias, qApp, for the cases in which a component such as +MyWidget needs to talk to the application object. +<p> <pre> int main( int argc, char **argv ) + { + <a href="qapplication.html">QApplication</a> a( argc, argv ); + + MyWidget w; + w.<a href="qwidget.html#setGeometry">setGeometry</a>( 100, 100, 200, 120 ); + <a name="x2305"></a> a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &w ); + <a name="x2309"></a> w.<a href="qwidget.html#show">show</a>(); + <a name="x2303"></a> return a.<a href="qapplication.html#exec">exec</a>(); + } +</pre> +<p> Here we instantiate our new child, set it to be the main widget, and +execute the application. +<p> <h2> Behavior +</h2> +<a name="2"></a><p> This program is very similar in behavior to the previous one. The +difference lies in the way we have implemented it. It does behave +slightly differently, however. Just try to resize it to see. +<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a +makefile and build the application.) +<p> <h2> Exercises +</h2> +<a name="3"></a><p> Try to create another MyWidget object in main(). What happens? +<p> Try to add more buttons or put in widgets other than <a href="qpushbutton.html">QPushButton</a>. +<p> You're now ready for <a href="tutorial1-05.html">Chapter 5.</a> +<p> [<a href="tutorial1-03.html">Previous tutorial</a>] +[<a href="tutorial1-05.html">Next tutorial</a>] +[<a href="tutorial.html">Main tutorial page</a>] +<p> +<!-- eof --> +<p><address><hr><div align=center> +<table width=100% cellspacing=0 border=0><tr> +<td>Copyright © 2007 +<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a> +<td align=right><div align=right>Qt 3.3.8</div> +</table></div></address></body> +</html> |