Qt4编程指南：C++ GUI实践

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"C++ Gui Programming with Qt 4" 《C++ GUI Programming with Qt 4》是Jasmin Blanchette和Mark Summerfield合著的一本专著，由Prentice Hall出版社于2008年2月4日出版，旨在全面介绍Qt 4框架，帮助读者轻松入门并掌握C++下的图形用户界面编程。本书适用于Windows、Linux/Unix、Mac OS X以及嵌入式Linux平台，无需修改源代码即可实现跨平台运行。书中的内容涵盖了Qt 4.3的所有核心特性，包括最新的Qt编程模式和最佳实践。作者们作为Trolltech（现为Nokia）的内部专家，确保了书中提供的指导和示例具有权威性。全书共有752页，包含了丰富的实例和深入的建议，是Trolltech用于培训新员工的官方教材。本书重点介绍了以下几个方面的内容： 1. **模型/视图架构**：详细讲解如何实现和利用Qt的模型/视图架构，这是一种强大的设计模式，允许分离数据模型与用户界面，提供灵活的数据展示和操作方式。 2. **图形系统改进**：针对Qt 4.3更新的图形支持，介绍如何利用这些改进来创建更高效、更美观的用户界面，包括2D图形和动画效果。 3. **数据库访问**：提供了如何集成和使用Qt的数据库模块（如QSql）来连接和操作各种数据库系统的实例，支持SQL标准以及多种数据库驱动。 4. **XML集成**：探讨了如何利用Qt的XML支持来读写XML文件，以及如何将XML数据与应用程序的其他部分集成。 5. **子类化和扩展**：深入讲解如何通过子类化Qt的类来扩展其功能，满足特定项目需求，同时保持代码的可维护性和灵活性。 6. **事件处理和网络编程**：介绍Qt的事件机制，以及如何进行网络通信，包括HTTP、FTP和TCP/IP协议的使用。 7. **国际化和本地化**：阐述如何使用Qt工具和API实现应用程序的多语言支持，适应全球用户。 8. **性能优化和调试**：提供了一些关于如何优化Qt应用程序性能和进行有效调试的技巧和策略。此外，书中的索引和目录结构使得读者能够快速定位到感兴趣的主题，无论是初学者还是经验丰富的开发者，都能从中受益匪浅。这本书不仅适合个人自学，也适合作为大学或培训机构的教材，帮助学习者掌握Qt 4的精髓，提升GUI开发能力。

展开

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.