From d796c9dd933ab96ec83b9a634feedd5d32e1ba3f Mon Sep 17 00:00:00 2001 From: Timothy Pearson Date: Tue, 8 Nov 2011 12:31:36 -0600 Subject: Test conversion to TQt3 from Qt3 8c6fc1f8e35fd264dd01c582ca5e7549b32ab731 --- doc/html/tutorial1-07.html | 213 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 213 insertions(+) create mode 100644 doc/html/tutorial1-07.html (limited to 'doc/html/tutorial1-07.html') diff --git a/doc/html/tutorial1-07.html b/doc/html/tutorial1-07.html new file mode 100644 index 000000000..a54ef7803 --- /dev/null +++ b/doc/html/tutorial1-07.html @@ -0,0 +1,213 @@ + + + + + +TQt Tutorial - Chapter 7: One Thing Leads to Another + + + + + + + +

TQt Tutorial - Chapter 7: One Thing Leads to Another

+ + +

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 t7 subdirectory. +

t7/lcdrange.h contains the LCDRange class definition. +
t7/lcdrange.cpp contains the LCDRange implementation. +
t7/main.cpp contains MyWidget and main. +

Line-by-line Walkthrough +

t7/lcdrange.h +

This file is mainly lifted from main.cpp in +Chapter 6; only the changes are noted here. +

+ +

    #ifndef LCDRANGE_H
+    #define LCDRANGE_H
+

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 all of the +header file. +

    #include <qvbox.h>
+

qvbox.h is included. LCDRange inherits TQVBox, and the header file +of a parent class must always be included. We cheated a bit in the +previous chapters, and we let qwidget.h be included indirectly via +other header files such as qpushbutton.h. +

    class TQSlider;
+

This is another classic trick, but one that's much less used often. Because +we don't need TQSlider in the interface 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 TQSlider in the .cpp +file. +

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. +

    class LCDRange : public TQVBox
+    {
+        Q_OBJECT
+    public:
+        LCDRange( TQWidget *parent=0, const char *name=0 );
+

Note the Q_OBJECT. This macro must be included in all classes that +contain signals and/or slots. If you are curious, it defines the +functions that are implemented in the +meta object file. +

        int value() const;
+    public slots:
+        void setValue( int );
+
+    signals:
+        void valueChanged( int );
+

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. +

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. +

Slots must be implemented in the normal way (remember that a slot is also +a C++ member function). Signals are automatically implemented in the +meta object 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). +

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 somethingChanged(). +

t7/lcdrange.cpp +

+ +

This file is mainly lifted from t6/main.cpp, and +only the changes are noted here. +

        connect( slider, SIGNAL(valueChanged(int)),
+                 lcd, SLOT(display(int)) );
+        connect( slider, SIGNAL(valueChanged(int)),
+                 SIGNAL(valueChanged(int)) );
+

This code is from the LCDRange constructor. +

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 signal. Connect() with 3 arguments always +connects to signals or slots in this object. +

Yes, that's right. Signals can be connected to other signals. When +the first is emitted, the second signal is also emitted. +

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 +TQLCDNumber and to the valueChanged() signal of the LCDRange. +

Thus, when the signal is emitted, LCDRange emits its own +valueChanged() signal. In addition, TQLCDNumber::display() is called +and shows the new number. +

Note that you're not guaranteed any particular order of execution - +LCDRange::valueChanged() may be emitted before or after +TQLCDNumber::display()and is entirely arbitrary. +

    int LCDRange::value() const
+    {
+        return slider->value();
+    }
+

The implementation of value() is straightforward; it simply returns +the slider's value. +

    void LCDRange::setValue( int value )
+    {
+        slider->setValue( value );
+    }
+

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. +

t7/main.cpp +

+ +

        LCDRange *previous = 0;
+        for( int r = 0 ; r < 4 ; r++ ) {
+            for( int c = 0 ; c < 4 ; c++ ) {
+                LCDRange* lr = new LCDRange( grid );
+                if ( previous )
+                    connect( lr, SIGNAL(valueChanged(int)),
+                             previous, SLOT(setValue(int)) );
+                previous = lr;
+            }
+        }
+

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 signal/slot 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. +

Compiling +

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: +

+qmake -project
+qmake
+

+ +

The first command tells qmake to +create a .pro (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 make (or nmake if you're using Visual +Studio) to build your application. +

Behavior +

On startup, the program's appearance is identical to the previous one. +Try operating the slider to the bottom right... +

Exercises +

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. +

Click to the left of the handle on the bottom right slider. What +happens? Why is this the correct behavior? +

You're now ready for Chapter 8. +

[Previous tutorial] +[Next tutorial] +[Main tutorial page] +

+ +

Trademarks +

TQt 3.3.8

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