C++ Qt4入门指南：从基础到高级GUI开发

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"C++ GUI Programming with Qt" 是一本由 Jasmin Blanchette 和 Mark Summerfield 合著的专业教材，它为初学者提供了全面学习 Qt 开发的绝佳指南。该书由 Prentice Hall 出版，于2006年6月21日发行，拥有印制版 ISBN-10:0-13-187249-4 和 ISBN-13:978-0-13-187249-3。全书共计560页，内容涵盖了Qt 4.1的深度使用，这是Trolltech官方推荐的最佳实践指导。这本书的核心内容聚焦于如何利用 C++ 实现高效、工业级的图形用户界面 (GUI) 应用程序，这些应用可以无缝运行在 Windows、Linux/Unix、MacOS X 和嵌入式 Linux 等多种平台上，无需对源代码进行过多调整。作者们作为Trolltech内部专家，从头到尾详细讲解了如何在 Qt 4.1 的强大功能上取得卓越成果，包括其模型/视图架构（Model-View Architecture）和强大的2D绘图引擎。书中深入剖析了Qt的关键技术，让读者掌握最有效的编程模式和技巧。读者将了解到Qt事件模型和布局系统的运作机制，并通过实际案例，逐步了解从基础GUI开发到高级数据库和XML集成的高级技术。特别值得关注的是，书中新增了关于Qt 4.1模型/视图架构的章节，这对于理解如何组织和管理复杂的数据与视图关系至关重要。这是一本全面且实用的教程，对于希望在C++环境中使用Qt进行GUI开发的开发者来说，无论是入门者还是有一定经验的程序员，都能从中受益匪浅。通过阅读和实践书中的内容，读者将能够建立起坚实的Qt开发基础，并提升自己的技能水平。

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

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

This document is created with trial version of CHM2PDF Pilot 2.11.

(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

In lines 19 to 22, we lay out the spin box and slider widgets using a layout manager. A layout manager is an object

that sets the size and position of the widgets that lie under its responsibility. Qt has three main layout manager

classes:



QHBoxLayout

lays out widgets horizontally from left to right (right to left for some cultures).



QVBoxLayout

lays out widgets vertically from top to bottom.



QGridLayout

lays out widgets in a grid.

The call to

QWidget::setLayout()

on line 22 installs the layout manager on the window. Behind the scenes, the

QSpinBox

and

QSlider

are "reparented" to be children of the widget on which the layout is installed, and for this

reason we don't need to specify an explicit parent when we construct a widget that will be put in a layout.

Figure 1.6. The Age application's widgets

Even though we didn't set the position or size of any widget explicitly, the

QSpinBox

and

QSlider

appear nicely laid

out side by side. This is because

QHBox -Layout

automatically assigns reasonable positions and sizes to the widgets

for which it is responsible, based on their needs. The layout managers free us from the chore of hard-coding screen

positions in our applications and ensure that windows resize smoothly.

Qt's approach to building user interfaces is simple to understand and very flexible. The most common pattern that Qt

programmers use is to instantiate the required widgets and then set their properties as necessary. Programmers add

the widgets to layouts, which automatically take care of sizing and positioning. User interface behavior is managed

by connecting widgets together using Qt's signals and slots mechanism.

This document is created with trial version of CHM2PDF Pilot 2.11.

http://doc.trolltech.com/ . This site also has selected articles from Qt Quarterly, the Qt programmers' newsletter

sent to all commercial licensees.

This chapter has introduced the key concepts of signalslot connections and layouts. It has also begun to reveal Qt's

consistent and fully object-oriented approach to the construction and use of widgets. If you browse through Qt's

documentation, you will find a uniformity of approach that makes it straightforward to learn how to use new widgets,

and you will also find that Qt's carefully chosen names for functions, parameters, enums, and so on, make

programming in Qt surprisingly pleasant and easy.

The following chapters of Part I build on the fundamentals covered here, showing how to create complete GUI

applications with menus, toolbars, document windows, a status bar, and dialogs, along with the underlying

functionality to read, process, and write files.

Widget Styles

The screenshots we have seen so far have been taken on Linux, but Qt applications look native on

every supported platform. Qt achieves this by emulating the platform's look and feel, rather than

wrapping a particular platform or toolkit's widget set.

Figure 1.9. Styles available everywhere

With Qt/X11 and Qtopia Core, the default style is Plastique, which uses gradients and anti-aliasing to

provide a modern look and feel. Qt application users can override the default style by using the

-style

command-line option. For example, to launch the Age application using the Motif style on X11, simply

type

./age -style motif

on the command line.

Figure 1.10. Platform-

specific styles

Unlike the other styles, the Windows XP and Mac styles are only available on their native platforms,

since they rely on the platforms' theme engines.

This document is created with trial version of CHM2PDF Pilot 2.11.

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