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### 1. Introduction

### 1.1 What KDE provides

The K Desktop Environment offers an easy way for application designers to equip their products with an intuitive way of user interaction. It provides all means to solve common tasks using a set of library classes that extend the facilities of the Qt toolkit. This allows for a unique look and feel to applications as well as interaction with other programs and the window manager. This handbook provides an introduction to the usage of the KDE libraries, shipped with KDE, to enable developers to find easy solutions for common programming issues. It also explains why certain techniques and classes should be used when creating applications that are targeting the K Desktop Environment.

Basically, KDE offers a set of standards that allow a unique look and usage of applications that should be watched when designing programs. A lot of tasks are done automatically, such as:

- Session Management
- Standard keyboard accelerator configuration
- Font, Color and Style changing
- Theme support (KDE 1.1.2 and higher)
- Internationalization

Therefore, theses issues only have to be mentioned in their functionality for complete information. Application developers only have to care about what their program is intended to do and where KDE can help. There, KDE offers user interfaces that extend the Qt toolkit where necessary. If both libraries offer similar solutions, KDE developers should (in most cases) use the methods provided by the KDE libraries.

KDE offers a set of widgets that can be used for creating application specific dialogs and views. Examples are

- KSeparator, offering a common separator line
- KColorButton, offering a push button displaying a color

Normally, applications ask the user to select various values. Here, the libraries provide easy means to get these values by complex widgets that are ready to use and are already known to the user by the KDE desktop, such as:

- File dialogs,
- Color dialogs,
- Font dialogs,
- Keyboard configuration dialogs

These should be used wherever a user setting is required as it simplifies the programmer's work, extends the application's facilities dramatically and provide a common look.

The Qt library is addressed in this handbook as far as it offers solutions not provided by KDE, but as information about event handling and the signal/slot mechanism is hard to find for developers, this turned out to be a special chapter in this handbook.

### 1.2 Notes about KDE 2 / Qt 2.0

As you may have guessed, this handbook explicitely adresses KDE 1.x development using the Qt 1.4x libraries. You may ask "Hey, Qt's 2.0 version is released already, why not talk only about that ?" - but there are several issues that result in a need for a KDE 1.x reference.

The issues that lead to this are first of all that developers should consider the KDE 1.x series the stable desktop and development environment. As long as KDE 2 (which introduces Qt 2.0 as well) is under development, programmers will have a hard time to follow the changes, which means a high time-consuming search for information and, if you experience bugs, error searching. There are projects covered by the KDE core team that ensure the KDE 2 libraries will work - the KDE itself as well as the supplying applications and the KOffice suite. Nevertheless, developers who are starting or developing projects for KDE now have the choice and those that want to rely on the stable environment will also want to port their applications to KDE 2 to make it usable on one hand and to implement improvements that are introduced by new library functions. Therefore information about where KDE and Qt differ from the 1.x series in future releases have been included as footnotes as far as changes are known to the author at the time of this writing and doesn't claim to be in any way complete. Explanations of classes that are still in the KDE 1.x API but are already removed in the current KDE 2 API are left out to avoid any trouble when porting to KDE 2.

In further versions of this handbook KDE 2 development will be addressed completely and the according chapters revisited for the changes this implies.

### 1.3 About this Handbook

This handbook has been written in order to give developers a guideline to the usage of the KDE 1.x libraries in general in conjunction with the Qt 1.4x library on X11 desktop systems. It cannot replace any programming knowledge that is needed for C++ programming and covers the Qt classes where necessary. You should in any case look at the page "Structure Overview" of the Qt online reference which contains a general guidance to the Qt library by class usage in general. This handbook tries to follow this structure to complete your knowledge about where KDE classes are appropriate and explains the technique of KDE application development by describing class usage on topics.

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