Qt4.3编程指南：C++ GUI实践

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"C++ GUI Programming with Qt4" 是一本由 Jasmin Blanchette 和 Mark Summerfield 合著的书籍，由 Prentice Hall 出版，第二版发布于2008年2月4日，主要关注使用Qt 4.3进行C++图形用户界面（GUI）编程。该书提供了跨平台的解决方案，支持在Windows、Linux/Unix、Mac OS X以及嵌入式Linux系统上无源代码更改地运行应用程序。书中内容涵盖了Qt的官方最佳实践，是Trolltech（现为Nokia所有）用来培训新员工的教程。本书的特点和主要内容包括： 1. **Qt 4.3的全面介绍**：详细讲解了Qt 4.3的主要功能和改进，包括新的图形支持和性能提升，为开发者提供了最新的开发工具和技术。 2. **模型/视图架构**：深入介绍了如何实现和利用Qt的模型/视图架构，这一架构允许分离数据模型和用户界面，从而提高了代码的可复用性和可维护性。 3. **图形系统增强**：详细讨论了Qt 4.3的图形支持，包括QGraphicsView和QGraphicsScene等组件，帮助开发者创建更复杂的用户界面和动画效果。 4. **数据库访问**：提供了解决方案，指导读者如何使用Qt的QSql模块与各种数据库进行交互，实现高效的数据存储和检索。 5. **XML集成**：介绍了如何利用Qt的XML支持来读取、写入和处理XML文档，增强了应用程序的数据交换能力。 6. **子类化和插件**：阐述了如何通过子类化Qt的类来扩展其功能，以及如何构建和使用插件系统，增加应用程序的灵活性和可扩展性。 7. **网络编程**：涵盖了网络通信的基础，包括HTTP、FTP等协议的使用，使开发者能够构建可以联网的应用程序。 8. **国际化和本地化**：详细讲解了如何使应用程序适应不同的语言和文化，包括使用Qt的QTranslator和QLocale类。 9. **调试和测试**：提供了有关如何有效地调试和测试Qt应用程序的策略，以确保代码的质量和稳定性。 10. **实例丰富**：书中包含大量实际示例，让读者能够通过实践学习，加深理解并快速掌握Qt编程技巧。《C++ GUI Programming with Qt4》是一本面向C++程序员的权威指南，无论初学者还是经验丰富的开发者，都能从中受益，提升在Qt平台上开发高质量GUI应用的能力。通过这本书，读者将能够构建出强大、稳定且具有吸引力的跨平台应用程序。

It is now possible to try the program on your own machine. It should look like the one shown in Figure 1.1. First, you will need to

install Qt 4.3.2 (or a later Qt 4 release), a process that is explained in Appendix A. From now on, we will assume that you have a

correctly installed copy of Qt 4 and that Qt's bin directory is in your PATH environment variable. (On Windows, this is done

automatically by the Qt installation program.) You will also need the program's code in a file called hello.cpp in a directory

called hello. You can type in hello.cpp yourself or copy it from the examples that accompany this book, where it is

available as examples/chap01/hello/hello.cpp. (All the examples are available from the book's web site,

http://www.informit.com/title/0132354160.)

Figure 1.1. Hello on Linux

From a command prompt, change the directory to hello, and type

qmake -project

to create a platform-independent project file (hello.pro), and then type

qmake hello.pro

to create a platform-specific makefile from the project file. (The qmake tool is covered in more detail in Appendix B.) Type

make to build the program. Run it by typing hello on Windows, ./hello on Unix, and open hello.app on Mac OS X.

To terminate the program, click the close button in the window's title bar.

If you are using Windows and have installed the Qt Open Source Edition and the MinGW compiler, you will have a shortcut to an

MS-DOS Prompt window that has all the environment variables correctly set up for Qt. If you start this window, you can compile

Qt applications within it using qmake and make as described previously. The executables produced are put in the application's

debug or release folder (e.g., C:\examples\chap01\hello\release\hello.exe).

If you are using Microsoft Visual C++ with a commercial version of Qt, you will need to run nmake instead of make.

Alternatively, you can create a Visual Studio project file from hello.pro by typing

qmake -tp vc hello.pro

and then build the program in Visual Studio. If you are using Xcode on Mac OS X, you can generate an Xcode project using the

command

qmake -spec macx-xcode hello.pro

Before we go on to the next example, let's have some fun: Replace the line

QLabel *label = new QLabel("Hello Qt!");

with

QLabel *label = new QLabel("<h2><i>Hello</i> "

"<font color=red>Qt!</font></h2>");

and rebuild the application. When run, it should look like Figure 1.2. As the example illustrates, it's easy to brighten up a Qt

application's user interface using some simple HTML-style formatting.

Figure 1.2. A label with basic HTML formatting

Part I: Basic Qt

1. Getting Started

Hello Qt•

Making Connections•

Laying Out Widgets•

Using the Reference Documentation•

This chapter shows how to combine basic C++ with the functionality provided by Qt to create a few small graphical user interface

(GUI) applications. This chapter also introduces two key Qt ideas: "signals and slots" and layouts. In Chapter 2, we will go into

more depth, and in Chapter 3, we will start building a more realistic application.

If you already know Java or C# but have limited experience with C++, you might want to start by reading the C++ introduction in

Appendix D.

Hello Qt

Let's start with a very simple Qt program. We will first study it line by line, and then see how to compile and run it.

1 #include <QApplication>

2 #include <QLabel>

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

4 {

5 QApplication app(argc, argv);

6 QLabel *label = new QLabel("Hello Qt!");

7 label->show();

8 return app.exec();

9 }

Lines 1 and 2 include the definitions of the QApplication and QLabel classes. For every Qt class, there is a header file with

the same name (and capitalization) as the class that contains the class's definition.

Line 5 creates a QApplication object to manage application-wide resources. The QApplication constructor requires argc

and argv because Qt supports a few command-line arguments of its own.

Line 6 creates a QLabel widget that displays "Hello Qt!". In Qt and Unix terminology, a widget is a visual element in a user

interface. The term stems from "window gadget" and is the equivalent of both "control" and "container" in Windows terminology.

Buttons, menus, scroll bars, and frames are all examples of widgets. Widgets can contain other widgets; for example, an

application window is usually a widget that contains a QMenuBar, a few QToolBars, a QStatusBar, and some other widgets.

Most applications use a QMainWindow or a QDialog as the application window, but Qt is so flexible that any widget can be a

window. In this example, the QLabel widget is the application window.

Line 7 makes the label visible. Widgets are always created hidden so that we can customize them before showing them, thereby

avoiding flicker.

Line 8 passes control of the application on to Qt. At this point, the program enters the event loop. This is a kind of stand-by mode

where the program waits for user actions such as mouse clicks and key presses. User actions generate events (also called

"messages") to which the program can respond, usually by executing one or more functions. For example, when the user clicks a

widget, a "mouse press" and a "mouse release" event are generated. In this respect, GUI applications differ drastically from

conventional batch programs, which typically process input, produce results, and terminate without human intervention.

For simplicity, we don't bother calling delete on the QLabel object at the end of the main() function. This memory leak is

harmless in such a small program, since the memory will be reclaimed by the operating system when the program terminates.