UI -Control Framework Overview

Description

Controls

A -control is a rectangular area of a window that may respond to user input. -Controls have a number of properties that determine their behavior and their -relationships to other controls and windows.

A control is represented -by the class CCoeControl.

A simple control is -one which contains no other controls.

A container control is -one which contains one or more controls. A container control is also referred -to as a compound control. The contained controls may themselves be -container controls. When a control is contained in a container control it -is called a component control. A component control is always redrawn -when its container control is redrawn.

The following diagram shows -simple controls in orange and container controls in grey.

- Simple and compound controls - -

Controls and Windows

A window may be considered -as a transparent layer. Windows are managed by the Window Server and described elsewhere. A control -provides a means of access to a window - it can be drawn onto the window and -can receive input.

Each window has a one-to-one relationship with -a single control that covers it precisely. This control is referred to as -a window-owning control. A window-owning control shares the behavior -of its window, in particular the parent-child window relationships which govern -the window's position and overlapping behavior.

A non-window-owning -control typically covers only part of a window. It cannot be moved around -on the screen independently of its window, cannot draw outside its window -and is always a component control.

You might think of a window-owning -control as a piece of glass and a non-window-owning control as a sticker on -a window-owning control.

Application User Interface (AppUi) framework

The -application user interface framework provides support for the distribution -of key events to an application's controls. It maintains a control stack to -which an application must add all the top-level container controls that it -wishes to handle key events, setting a priority for each. When a key event -occurs, the framework offers it to each control on the stack in priority order -until it is consumed.

The application user interface framework is -provided by the base class CCoeAppUi. UIKON and UI variants -specialize CCoeAppUi further. Applications derive from the -variant AppUi.

CCoeAppUi provides a simplified -interface to the View -Server which enables seamless switching between different views across -various applications.

Control Environment (CoeEnv)

The -Control Environment simplifies the interface to the Window Server and provides -an environment for creating controls. It is a single instance (a singleton) -of the class CCoeEnv which encapsulates an active scheduler -and active objects for communicating with the window server. CCoeEnv is -created automatically by the framework and a pointer stored in Thread Local -Storage (TLS). It is available through CCoeControl::CoeEnv(), CCoeAppUi::CoeEnv() and -through its own static function, CCoeEnv::Static(), which -is less efficient.

The control environment also provides simplified -access to drawing functions, fonts, and resource files which are used by most -applications.