使用 Qt 4.3 构建工业级 C++ 应用程序

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"C++ GUI Programming with Qt 4, Second Edition" 本书是关于使用 Qt 4 进行 C++ 图形用户界面编程的权威指南。 Qt 是一个跨平台的应用程序开发框架，由 Trolltech 公司开发，现已被诺基亚公司收购。该框架提供了一个功能强大且灵活的工具集，允许开发者使用 C++ 语言创建高性能的图形用户界面应用程序。在这本书中，作者 Jasmin Blanchette 和 Mark Summerfield 共同介绍了如何使用 Qt 4 创建工业级别的 C++ 应用程序。他们提供了大量的实践示例和深入的建议，帮助读者快速掌握 Qt 4 的所有方面。本书的内容涵盖了 Qt 4 的所有主要方面，从模型/视图架构的实现到使用 Qt 4 的改进图形支持。读者将学习如何使用 Qt 4 实现各种 GUI 开发任务，如数据库访问、XML 集成和子类设计。 Qt 4 的重要特点包括： * 跨平台支持：Qt 4 支持 Windows、Linux/Unix、MacOS X 和嵌入式 Linux 等多个平台。 * 性能优越：Qt 4 使用 C++ 语言实现，提供了高性能的图形用户界面应用程序。 * 灵活性强：Qt 4 提供了一个灵活的工具集，允许开发者快速创建复杂的 GUI 应用程序。本书适合 C++ 程序员、Qt 开发者和 GUI 应用程序开发人员。知识点： 1. Qt 4 的概述和特点 2. 使用 Qt 4 创建工业级别的 C++ 应用程序 3. 模型/视图架构的实现 4. 使用 Qt 4 的改进图形支持 5. 数据库访问和 XML 集成 6. 子类设计和实现 7. Qt 4 的跨平台支持 8. Qt 4 的性能优越和灵活性强本书是 Qt 4 编程的权威指南，提供了大量的实践示例和深入的建议，帮助读者快速掌握 Qt 4 的所有方面。

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.