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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/tutorial1-07.html | |
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diff --git a/doc/html/tutorial1-07.html b/doc/html/tutorial1-07.html new file mode 100644 index 0000000..11c08b0 --- /dev/null +++ b/doc/html/tutorial1-07.html @@ -0,0 +1,213 @@ +<!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:670 --> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>Qt Tutorial - Chapter 7: One Thing Leads to Another</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 7: One Thing Leads to Another</h1> + + +<p> <center><img src="t7.png" alt="Screenshot of tutorial seven"></center> +<p> This example shows how to create custom widgets with signals and +slots, and how to connect them together in more complex ways. For the +first time, the source is split among several files which we've placed +in the <tt>t7</tt> subdirectory. +<p> <ul> +<li> <a href="t7-lcdrange-h.html">t7/lcdrange.h</a> contains the LCDRange class definition. +<li> <a href="t7-lcdrange-cpp.html">t7/lcdrange.cpp</a> contains the LCDRange implementation. +<li> <a href="t7-main-cpp.html">t7/main.cpp</a> contains MyWidget and main. +</ul> +<p> <h2> Line-by-line Walkthrough +</h2> +<a name="1"></a><p> <h3> <a href="t7-lcdrange-h.html">t7/lcdrange.h</a> +</h3> +<a name="1-1"></a><p> This file is mainly lifted from <a href="tutorial1-06.html#main">main.cpp</a> in +Chapter 6; only the changes are noted here. +<p> + +<p> <pre> #ifndef LCDRANGE_H + #define LCDRANGE_H +</pre> +<p> This is the classic C construction to avoid errors if a header file +happens to be included more than once. If you don't use it already, +it is a very good habit to develop. The #ifndef should enclose <em>all</em> of the +header file. +<p> <pre> #include <<a href="qvbox-h.html">qvbox.h</a>> +</pre> +<p> <a href="qvbox-h.html">qvbox.h</a> is included. LCDRange inherits <a href="qvbox.html">QVBox</a>, and the header file +of a parent class must always be included. We cheated a bit in the +previous chapters, and we let <a href="qwidget-h.html">qwidget.h</a> be included indirectly via +other header files such as <a href="qpushbutton-h.html">qpushbutton.h</a>. +<p> <pre> class QSlider; +</pre> +<p> This is another classic trick, but one that's much less used often. Because +we don't need <a href="qslider.html">QSlider</a> in the <em>interface</em> of the class, only in the +implementation, we use a forward declaration of the class in the +header file and include the header file for QSlider in the .cpp +file. +<p> This makes the compilation of big projects much faster, because when a +header file has changed, fewer files need to be recompiled. It can +often speed up big compilations by a factor of two or more. +<p> <pre> class LCDRange : public <a href="qvbox.html">QVBox</a> + { + <a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a> + public: + LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 ); +</pre> +<p> Note the Q_OBJECT. This macro must be included in <em>all</em> classes that +contain signals and/or slots. If you are curious, it defines the +functions that are implemented in the +<a href="metaobjects.html">meta object file</a>. +<p> <pre> int value() const; + public slots: + void setValue( int ); + + signals: + void valueChanged( int ); +</pre> +<p> These three members make up an interface between this widget and other +components in a program. Until now, LCDRange didn't really have an +interface at all. +<p> value() is a public function for accessing the value of the LCDRange. +setValue() is our first custom slot and valueChanged() is our first +custom signal. +<p> Slots must be implemented in the normal way (remember that a slot is also +a C++ member function). Signals are automatically implemented in the +<a href="signalsandslots.html">meta object</a> file. Signals follow the +access rules of protected C++ functions (i.e., they can be emitted only +by the class they are defined in or by classes inheriting from it). +<p> The signal valueChanged() is used when the LCDRange's value has +changed - just as you guessed from the name. This is not the last +signal you'll see called <i>something</i>Changed(). +<p> <h3> <a href="t7-lcdrange-cpp.html">t7/lcdrange.cpp</a> +</h3> +<a name="1-2"></a><p> + +<p> This file is mainly lifted from <a href="tutorial1-06.html#main">t6/main.cpp</a>, and +only the changes are noted here. +<p> <pre> <a name="x2333"></a> <a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), + <a name="x2330"></a> lcd, SLOT(<a href="qlcdnumber.html#display">display</a>(int)) ); + <a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), + SIGNAL(valueChanged(int)) ); +</pre> +<p> This code is from the LCDRange constructor. +<p> The first connect is the same that you have seen in the previous chapter. +The second is new; it connects slider's valueChanged() signal to this +object's valueChanged <em>signal</em>. Connect() with 3 arguments always +connects to signals or slots in <tt>this</tt> object. +<p> Yes, that's right. Signals can be connected to other signals. When +the first is emitted, the second signal is also emitted. +<p> Let's look at what happens when the user operates the slider. The +slider sees that its value has changed and emits the valueChanged() +signal. That signal is connected both to the display() slot of the +<a href="qlcdnumber.html">QLCDNumber</a> and to the valueChanged() signal of the LCDRange. +<p> Thus, when the signal is emitted, LCDRange emits its own +valueChanged() signal. In addition, <a href="qlcdnumber.html#display">QLCDNumber::display</a>() is called +and shows the new number. +<p> Note that you're not guaranteed any particular order of execution - +LCDRange::valueChanged() may be emitted before or after +QLCDNumber::display()and is entirely arbitrary. +<p> <pre> int LCDRange::value() const + { + <a name="x2332"></a> return slider-><a href="qslider.html#value">value</a>(); + } +</pre> +<p> The implementation of value() is straightforward; it simply returns +the slider's value. +<p> <pre> void LCDRange::setValue( int value ) + { + <a name="x2331"></a> slider-><a href="qslider.html#setValue">setValue</a>( value ); + } +</pre> +<p> The implementation of setValue() is equally straightforward. Note +that because the slider and LCD number are connected, setting the +slider's value automatically updates the LCD number as well. In +addition, the slider will automatically adjust the value if it is +outside its legal range. +<p> <h3> <a href="t7-main-cpp.html">t7/main.cpp</a> +</h3> +<a name="1-3"></a><p> + +<p> <pre> LCDRange *previous = 0; + for( int r = 0 ; r < 4 ; r++ ) { + for( int c = 0 ; c < 4 ; c++ ) { + LCDRange* lr = new LCDRange( grid ); + if ( previous ) + <a href="qobject.html#connect">connect</a>( lr, SIGNAL(valueChanged(int)), + previous, SLOT(setValue(int)) ); + previous = lr; + } + } +</pre> +<p> All of main.cpp is copied from the previous chapter except in +the constructor for MyWidget. When we create the 16 LCDRange object, we +now connect them using the <a href="signalsandslots.html">signal/slot</a> mechanism. Each has its valueChanged() signal +connected to the setValue() slot in the previous one. Because LCDRange +emits the signal valueChanged() when its value changes (surprise!), we +are here creating a "chain" of signals and slots. +<p> <a name="compiling"></a> +<h2> Compiling +</h2> +<a name="2"></a><p> Creating a makefile for a multi-file application is no different from +creating one for a single-file application. If you've saved all the +files in this example in their own directory, all you have to do is: +<pre> +qmake -project +qmake +</pre> + +<p> The first command tells <a href="qmake-manual.html">qmake</a> to +create a <tt>.pro</tt> (project) file. The second command tells it to create +a (platform-specific) makefile based on the project file. You should +now be able to type <tt>make</tt> (or <tt>nmake</tt> if you're using Visual +Studio) to build your application. +<p> <h2> Behavior +</h2> +<a name="3"></a><p> On startup, the program's appearance is identical to the previous one. +Try operating the slider to the bottom right... +<p> <h2> Exercises +</h2> +<a name="4"></a><p> Use the bottom right slider to set all LCDs to 50. Then set the top +half to 40 by clicking once to the left of the slider handle. Now, +use the one to the left of the last one operated to set the first +seven LCDs back to 50. +<p> Click to the left of the handle on the bottom right slider. What +happens? Why is this the correct behavior? +<p> You're now ready for <a href="tutorial1-08.html">Chapter 8.</a> +<p> [<a href="tutorial1-06.html">Previous tutorial</a>] +[<a href="tutorial1-08.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> |