From bd0f3345a938b35ce6a12f6150373b0955b8dd12 Mon Sep 17 00:00:00 2001 From: Timothy Pearson Date: Sun, 10 Jul 2011 15:24:15 -0500 Subject: Add Qt3 development HEAD version --- doc/html/tutorial1-01.html | 168 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 168 insertions(+) create mode 100644 doc/html/tutorial1-01.html (limited to 'doc/html/tutorial1-01.html') diff --git a/doc/html/tutorial1-01.html b/doc/html/tutorial1-01.html new file mode 100644 index 0000000..ffda07a --- /dev/null +++ b/doc/html/tutorial1-01.html @@ -0,0 +1,168 @@ + + + + + +Qt Tutorial - Chapter 1: Hello, World! + + + + + + + +

Qt Tutorial - Chapter 1: Hello, World!

+ + +

This first program is a simple hello-world example. It contains only +the bare minimum you need to get a Qt application up and running. +The picture above is a snapshot of this program. +

/****************************************************************
+**
+** Qt tutorial 1
+**
+****************************************************************/
+
+#include <qapplication.h>
+#include <qpushbutton.h>
+
+
+int main( int argc, char **argv )
+{
+    QApplication a( argc, argv );
+
+    QPushButton hello( "Hello world!", 0 );
+    hello.resize( 100, 30 );
+
+    a.setMainWidget( &hello );
+    hello.show();
+    return a.exec();
+}
+

+ + + +

Line-by-line Walkthrough +

    #include <qapplication.h>
+

This line includes the QApplication class definition. There has to be +exactly one QApplication object in every application that uses Qt. +QApplication manages various application-wide resources, such as the +default font and cursor. +

    #include <qpushbutton.h>
+

This line includes the QPushButton class definition. The +reference documentation for each class +mentions at the top which file needs to be included to use that class. +

QPushButton is a classical GUI push button that the user can press +and release. It manages its own look and feel, like every other QWidget. A widget is a user interface object that can process user +input and draw graphics. The programmer can change both the overall +look and feel and many minor +properties of it (such as color), as well as the widget's content. A +QPushButton can show either a text or a QPixmap. +

    int main( int argc, char **argv )
+    {
+

The main() function is the entry point to the program. Almost always +when using Qt, main() only needs to perform some kind of initialization +before passing the control to the Qt library, which then tells the +program about the user's actions via events. +

argc is the number of command-line arguments and argv is the +array of command-line arguments. This is a C/C++ feature. It is not +specific to Qt; however, Qt needs to process these arguments (see +following). +

        QApplication a( argc, argv );
+

a is this program's QApplication. Here it is created and processes +some of the command-line arguments (such as -display under X Window). +Note that all command-line arguments recognized by Qt are removed from +argv (and argc is decremented accordingly). See the QApplication::argv() documentation for details. +

Note: It is essential that the QApplication object be +created before any window-system parts of Qt are used. +

        QPushButton hello( "Hello world!", 0 );
+

Here, after the QApplication, comes the first window-system code: A +push button is created. +

The button is set up to display the text "Hello world!" and be a +window of its own (because the constructor specifies 0 for the parent +window, inside which the button should be located). +

        hello.resize( 100, 30 );
+

The button is set up to be 100 pixels wide and 30 pixels high (plus the +window system frame). In this case we don't care about the button's +position, and we accept the default value. +

        a.setMainWidget( &hello );
+

The push button is chosen as the main widget for the application. If +the user closes a main widget, the application exits. +

You don't have to have a main widget, but most programs do have one. +

        hello.show();
+

A widget is never visible when you create it. You must call show() to +make it visible. +

        return a.exec();
+

This is where main() passes control to Qt, and exec() will return when +the application exits. +

In exec(), Qt receives and processes user and system events and passes +these on to the appropriate widgets. +

}
+

You should now try to compile and run this program. +

Compiling +

To compile a C++ application you need to create a makefile. The +easiest way to create a makefile for Qt is to use the qmake build tool supplied with Qt. If you've +saved main.cpp in its 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) and then run your first Qt application! +

Behavior +

When you run it, you will see a small window filled with a single +button, and on it you can read the famous words, Hello World! +

Exercises +

Try to resize the window. Press the button. If you're running X +Window, try running the program with the -geometry option +(for example, -geometry 100x200+10+20). +

You're now ready for Chapter 2. +

[Next tutorial] +[Main tutorial page] +

+ +

Trademarks +

Qt 3.3.8

+ -- cgit v1.2.1