Qt4编程指南：打造跨平台C++ GUI应用

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“C++ GUI Programming with Qt4 是一本由 Jasmin Blanchette 和 Mark Summerfield 合著的专业书籍，由 Prentice Hall 出版社在2006年6月21日发行。该书专注于Qt 4.1版本的编程，提供了构建跨平台C++应用程序的全面指南，这些应用程序可在Windows、Linux/Unix、Mac OS X以及嵌入式Linux上原生运行，而无需修改源代码。这本书是Trolltech（现为Nokia的Qt部门）内部专家为开发者提供的官方最佳实践指导。通过本书，读者将深入理解Qt 4.1的各种高效编程模式和技术，涵盖从模型/视图架构到强大的新2D绘图引擎的关键技术。作者详细解析了Qt的事件模型和布局系统，并通过实际示例介绍了GUI开发、数据库集成和XML处理等方面的高级技巧。书中的新章节专门讨论了Qt 4的模型/视图架构，这是一个强大的设计模式，允许数据和用户界面分离，提高代码的可复用性和可维护性。此外，还涵盖了Qt的新插件系统，这使得开发者能够轻松扩展应用程序的功能，创建可动态加载的模块。书中的内容包括但不限于： 1. Qt基础知识：介绍Qt库的核心概念，包括信号与槽机制、对象系统和事件处理。 2. 用户界面设计：讲解如何使用Qt的QWidgets和QML构建用户界面，以及使用布局管理器优化界面布局。 3. 模型/视图编程：深入理解如何使用QAbstractItemModel、QListView、QTableView等类实现数据驱动的界面。 4. 绘图系统：探讨如何利用QPainter和QPaintEvent进行图形绘制，以及Qt的高级2D图形功能。 5. 文件和网络编程：介绍读写文件、目录操作以及网络通信API的使用。 6. 数据库集成：讲解如何使用QSql库连接和操作各种数据库，如SQLite、MySQL等。 7. XML支持：教授如何利用Qt的XML模块解析和生成XML文档。 8. 插件系统：学习如何创建和使用Qt插件，实现应用程序的可扩展性。 9. 嵌入式开发：对于希望在嵌入式设备上运行Qt应用的开发者，书中提供了相关指导。无论你是初学者还是有经验的Qt开发者，这本书都提供了丰富的资源和实践建议，帮助你充分利用Qt 4.1的强大功能，构建高效、健壮且跨平台的应用程序。”

instance, QPushButton emits a clicked() signal when the user clicks the button. A signal can be

connected to a function (called a slot in that context), so that when the signal is emitted, the slot is

automatically executed. In our example, we connect the button's clicked() signal to the

QApplication object's quit() slot. The SIGNAL() and SLOT() macros are part of the syntax; they are

explained in more detail in the next chapter.

[*]

Qt signals are unrelated to Unix signals. In this book, we are only concerned with Qt signals.

Figure 1.3. The Quit application

We will now build the application. We assume that you have created a directory called quit

containing quit.cpp. Run qmake in the quit directory to generate the project file, then run it again to

generate a makefile, as follows:

qmake -project

qmake quit.pro

Now build the application, and run it. If you click Quit, or press Space (which presses the button),

the application will terminate.

Laying Out Widgets

In this section, we will create a small example application that demonstrates how to use layouts to

manage the geometry of widgets in a window and how to use signals and slots to synchronize two

widgets. The application asks for the user's age, which the user can enter by manipulating either a

spin box or a slider.

The application consists of three widgets: a QSpinBox, a QSlider, and a QWidget. The QWidget is the

application's main window. The QSpinBox and the QSlider are rendered inside the QWidget; they are

children of the QWidget. Alternatively, we can say that the QWidget is the parent of the QSpinBox

and the QSlider. The QWidget has no parent itself because it is being used as a top-level window.

The constructors for QWidget and all of its subclasses take a QWidget * parameter that specifies the

parent widget.

Figure 1.4. The Age application

Here's the source code:

1 #include <QApplication>

2 #include <QHBoxLayout>

3 #include <QSlider>

4 #include <QSpinBox>

5 int main(int argc, char *argv[])

6 {

7 QApplication app(argc, argv);

8 QWidget *window = new QWidget;

9 window->setWindowTitle("Enter Your Age");

10 QSpinBox *spinBox = new QSpinBox;

11 QSlider *slider = new QSlider(Qt::Horizontal);

12 spinBox->setRange(0, 130);

13 slider->setRange(0, 130);

14 QObject::connect(spinBox, SIGNAL(valueChanged(int)),

15 slider, SLOT(setValue(int)));

16 QObject::connect(slider, SIGNAL(valueChanged(int)),

17 spinBox, SLOT(setValue(int)));

18 spinBox->setValue(35);

19 QHBoxLayout *layout = new QHBoxLayout;

20 layout->addWidget(spinBox);

21 layout->addWidget(slider);

22 window->setLayout(layout);

23 window->show();

24 return app.exec();

25 }

Lines 8 and 9 set up the QWidget that will serve as the application's main window. We call

setWindowTitle() to set the text displayed in the window's title bar.

Lines 10 and 11 create a QSpinBox and a QSlider, and lines 12 and 13 set their valid ranges. We can

safely assume that the user is at most 130 years old. We could pass window to the QSpinBox and

QSlider constructors, specifying that these widgets should have window as their parent, but it isn't

necessary here because the layout system will figure this out by itself and automatically set the

parent of the spin box and the slider, as we will see shortly.

The two QObject::connect() calls shown in lines 14 to 17 ensure that the spin box and the slider are

synchronized so that they always show the same value. Whenever the value of one widget changes,

its valueChanged(int) signal is emitted, and the setValue(int) slot of the other widget is called with

the new value.

Line 18 sets the spin box value to 35. When this happens, the QSpinBox emits the valueChanged(int)

signal with an int argument of 35. This argument is passed to the QSlider's setValue(int) slot,

which sets the slider value to 35. The slider then emits the valueChanged(int) signal, because its

own value changed, triggering the spin box's setValue(int) slot. But at this point, setValue(int)

doesn't emit any signal, since the spin box value is already 35. This prevents infinite recursion.

Figure 1.5 summarizes the situation.

Figure 1.5. Changing one widget's value changes both

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