深入探索Qt高级编程

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"QT高级编程，一份详细的PDF文档，涵盖了Qt的高级编程技术和应用，适合想要深入学习Qt的读者。" 在《高级Qt编程》这本书中，作者Mark Summerfield深入探讨了使用C++和Qt 4创建高质量软件的方法。Qt是一个强大的跨平台应用程序开发框架，广泛用于桌面、移动和嵌入式设备的软件开发。本书旨在帮助开发者充分利用Qt的强大功能，提升编程技能，并创造出卓越的软件产品。书中可能涵盖的知识点包括但不限于： 1. **Qt核心概念**：介绍Qt的基本架构，如信号与槽机制、事件处理系统以及对象模型，这些都是理解Qt工作原理的关键。 2. **Qt设计模式**：讨论Qt中实现的各种设计模式，如工厂模式、观察者模式等，这些模式使得代码更加可维护和可扩展。 3. **图形用户界面（GUI）编程**：详细讲解如何利用Qt Creator进行界面设计，以及Q widgets、QML等工具构建用户友好的图形界面。 4. **网络编程**：阐述如何使用Qt的网络模块进行TCP/IP通信、HTTP请求和数据传输，这对于开发网络应用程序至关重要。 5. **数据库集成**：介绍如何与各种数据库系统（如SQLite、MySQL等）连接和交互，以及使用Qt SQL模块进行查询和操作。 6. **多线程编程**：讲解如何在Qt环境中利用QThread实现并发和多线程，提高程序性能。 7. **国际化与本地化**：探讨如何为应用程序添加多语言支持，使软件适应不同地区的用户。 8. **单元测试与调试**：讲解如何使用Qt的测试框架（如Qt Test）进行代码测试，以及利用Qt Creator的调试工具找出并修复程序错误。 9. **性能优化**：提供优化Qt应用程序的策略和技巧，包括内存管理、减少CPU使用率等。 10. **移动与嵌入式开发**：介绍如何在Android、iOS等移动平台以及嵌入式设备上使用Qt进行开发。 11. **自定义控件和组件**：展示如何创建自定义的Qt组件，以满足特定项目需求。此外，书中可能还包含实际案例分析和示例代码，以帮助读者更好地理解和应用所学知识。同时，对于企业级别的批量购买或特殊销售，出版社还提供了折扣和定制服务，包括电子版和/或带有公司特定封面和内容的版本。通过深入学习《高级Qt编程》，开发者不仅能掌握Qt的高级技术，还能提升解决问题和开发复杂软件的能力，从而在软件工程领域取得更大的成就。

ptg

Forew ord

Way back in 1991, I sat on a park bench in Trondheim, Norway, together with

Haavard Nord. We were doing our non-military service together at the regional

hospital there, and needed to develop software for the storage and analysis of

ultrasound images. The hospital used all sorts of computers and wanted the

system to work on Unix, Mac, and Windows. This was a huge challenge and we

scanned the market for available class libraries that could help us. We were

appalled by the quality of what we found. On that park bench we decided to

come up with our own solution to the challenge.

We were young, ambitious, and naïve. Sick and tired of wasting our time ﬁnd-

ing out how to use non-intuitive tools and libraries,we set our sights on improv-

ing the situation. We wanted to change the world of software development ever

so slightly. Our goal was to make life easier for software developers. To make

it possible to focus on what we all know is the fun side of developing software:

being creative and turning out well-written code. So, we created the ﬁrst crude

versions of Qt, and incorporated Trolltech a few years later.

I think we achieved at least part of our goal. Qt has had tremendous success

since it was ﬁrst released in 1995.

In 2008 Trolltech was acquired by Nokia and in April 2009 it was time for

me to move on. After 15 years and 27 days in the company I was no longer on

the inside.

The product is in good hands, and the passion and hard work of the team are

the same as ever. The Trolls at Nokia are making sure that Qt continues to be

the rock solid framework you expect. Lars Knoll (of kHTML—WebKit—fame)

today leads almost 150 dedicated Qt engineers. Nokia has also added the

LGPL as a licensing option, making Qt accessible to even more developers.

This fall I was invited by Nokia as a guest of honor at the Qt Developer Days

in Munich, Germany. This user conference—which also takes place in the

U.S.—is a fantastic venue for Qt enthusiasts and has been increasing in size

year by year. It was great feeling the buzz and talking to Qt users from all

over Europe. I spoke to many developers who told me that Qt makes a real

difference in their software work. That makes an old hacker feel good.

Qt as a good tool and class library is only half the story behind its success. You

also need good documentation, tutorials, and books. After all, the goal was to

make life easier for developers.

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Introduction

For some time I have wanted to write a Qt book that covered topics that were

too advanced for C

GUI Programming with Qt 4,

★

even though that book

itself has proved quite challenging for some readers. There is also some

specialized material—not all of it difﬁcult—that I wanted to cover that simply

does not belong in a ﬁrst book on Qt programming. Furthermore, in view of

the sheer size of Qt, no one book can possibly do justice to all that it offers, so

there was clearly room for the presentation of new material.

What I’ve done in this book is to take a selection of modules and classes from

a variety of areas and shown how to make good use of them. The topics

chosen reﬂect both my own interests and also those that seem to result in the

most discussion on the

qt-interest

mailing list. Some of the topics are not

covered in any other book, while other topics cover more familiar ground—for

example, model/view programming. In all cases, I have tried to provide more

comprehensive coverage than is available elsewhere.

So the purposes of this book are to help Qt programmers deepen and broaden

their Qt knowledge and to increase the repertoire of what they can achieve

using Qt. The “advanced” aspect often refers more to what you will be able

to achieve than to the means of achieving it. This is because—as always—Qt

insulates us as far as possible from irrelevant detail and underlying complexity

to provide easy-to-use APIs that we can use simply and directly to great effect.

For example, we will see how to create a music player without having to know

anything about how things work under the hood; we will need to know only the

high-level API that Qt provides. On the other hand, even using the high-level

QtConcurrent module, the coverage of threading is necessarily challenging.

This book assumes that readers have a basic competence in C

programming,

and at least know how to create basic Qt applications—for example, having

read a good Qt 4 book, and having had some practical experience. Readers are

also assumed to be familiar with Qt’s reference documentation, at least as far

as being able to navigate it to look up the APIs of classes of interest. In addi-

tion, some chapters assume some basic topic-speciﬁc knowledge—for example,

Chapter 1 assumes some knowledge of JavaScript and web programming, and

the threading chapters assume a basic understanding of threading and Qt’s

threading classes. All these assumptions mean that this book can avoid ex-

★

GUI Programming with Qt 4, Second Edition, by Jasmin Blanchette and this author,

ISBN 0132354160.

ptg

2 Introduction

plaining many details and classes that are already familiar to Qt programmers,

such as using layouts, creating actions, connecting signals and slots, and so on,

leaving the book free to focus on the less familiar material.

Of course, no single volume book can realistically do justice to Qt’s more than

700 public classes—almost 800 in Qt 4.6—and its much more than one million

words of documentation, so no attempt is made to do so here. Instead this

book provides explanations and examples of how to use some of Qt’s most

powerful features, complementing the reference documentation rather than

duplicating it.

The book’s chapters have been designed to be as self-contained as possible, so

it is not necessary to read the book from beginning to end in chapter order. To

support this, where particular techniques are used in more than one chapter,

the explanation is given in just one place and cross-references are given else-

where. Nonetheless, if you plan to read odd chapters out of order, I recommend

that you at least do an initial skim read of the entire book, since chapters and

sections devoted to one particular topic may of necessity have material relating

to other topics. Also, I have tried to include lots of small details from Qt’s API

throughout, to make the book’s content richer, and to show as many features as

possible in context, so useful information appears throughout.

As with all my previous books, the quoted code snippets are of “live code”,

that is, the code was automatically extracted from the examples’ source ﬁles

and directly embedded in the PDF that went to the publisher—so there are

no cut and paste errors, and the code works. The examples are available from

www.qtrac.eu/aqpbook.html

and are licensed under the GPL (GNU General

Public License version 3). The book presents more than twenty-ﬁve examples

spread over more than 150

.hpp

and

.cpp

ﬁles, and amounting to well over

20 000 lines of code. Although all of the most important pieces of code are quot-

ed and explained in the book, there are numerous small details that there isn’t

space to cover in the book itself, so I recommend downloading the examples

and at least reading the source code of those examples that are in your areas

of particular interest. In addition to the examples, some modules containing

commonly used functionality are also provided. These all use the

AQP

names-

pace to make them easy to reuse, and they are all introduced in the ﬁrst couple

of chapters, and then used throughout the book.

All the examples—except for those in the last chapter which use Qt 4.6-speciﬁc

features—have been tested with Qt 4.5 and Qt 4.6 on Linux, Mac OS X, and

Windows. Applications built using Qt 4.5 will run unchanged with Qt 4.6, and

later Qt 4.x versions, because Qt maintains backward compatibility between

minor releases. However, where there are differences between the two Qt

versions, the book shows and explains the Qt 4.6-speciﬁc approach, while the

source code uses

#if QT_VERSION

so that the code compiles with either version

with the best practices used for each. A few examples may work with earlier

Qt 4.x versions, particularly Qt 4.4, and some examples could be backported to

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Introduction 3

an earlier Qt version—however, the focus of this book is purely on Qt 4.5 and

Qt 4.6, so there is no explicit coverage of backporting.

The book shows best Qt 4.6 practices, and despite Qt 4.6’s numerous new fea-

tures compared with Qt 4.5, this makes few differences to the code. One trivial

difference is that Qt 4.6 has a shortcut for the “quit” action and Qt 4.5 hasn’t;

the source code uses the shortcut for Qt 4.6 and has equivalent code for Qt 4.5

by using

#if QT_VERSION

. A much more important difference is that Qt 4.6 in-

troduced the

QGraphicsObject

class and also changed the behavior of graphics

items when it comes to communicating geometry changes. We explain the dif-

ferences in a sidebar and show the Qt 4.6 approach in the book’s code snippets,

but in the source code,

#if QT_VERSION

is used to show how to do the same things

using Qt 4.6 and Qt 4.5 or earlier, and using the best approach for both. In the

book’s last chapter, Qt 4.6-speciﬁc features are shown, with two out of the three

examples covered being conversions of examples presented earlier, and that

make use of the Qt 4.6 animation and state machine frameworks. Modifying

earlier examples makes it easier to see how to go from the traditional Qt ap-

proach to using the new frameworks.

The next version of Qt—Qt 4.7—will focus on stability, speed, and apart from

the new Qt Quick technology (which provides a means of creating GUIs declar-

atively using a JavaScript- like language), will introduce fewer new features

than in previous releases. Nonetheless, despite the huge ongoing development

effort that is being put into Qt, and its ever increasing scope, this book should

serve as a useful resource for learning about and using important Qt technolo-

gies in the Qt 4.x series, especially for Qt 4.5, Qt 4.6, and later versions,for some

years to come.

Acknowledgements

My ﬁrst acknowledgement is of my friend Trenton Schulz, an ex-senior soft-

ware engineer at Nokia’s Qt Development Frameworks (formerly Trolltech)

who is now a research scientist at the Norwegian Computing Center. Trenton

has proved to be a reliable, insightful, and challenging reviewer, whose careful

reading, high standards, and numerous suggestions have considerably helped

to improve this book.

My next acknowledgement is of another friend, Jasmin Blanchette, also an

ex-senior software engineer at Qt Development Frameworks, coauthor with

me of the C

GUI Programming with Qt 4 book, and now researching for a

PhD at the Technische Universität München. We both came up with the idea

for this book some time ago, and it is only due to pressure of work that he has

been an excellent—and demanding—reviewer, rather than coauthor.

I would also like to thank many people who work for (or worked for) Qt Develop-

ment Frameworks who read portions of the book and provided useful feedback,

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