Front -End Processor Overview

Purpose

Front End Processors, or FEPs, enable users -to input characters that are not on the device keyboard. For most phones a -FEP is essential for entering anything anything other than numbers. Typically -FEPs are used for processing multi-tap keypad input, predictive text, handwriting -recognition, voice recognition and character selection.

Architectural relationships

FEPs are ECOM plugins -that implement the FEP interface. They typically use the UI Control Framework -to intercept key and pointer events which are processed as necessary and the -output sent to the current application. Applications do not need to be aware -that a FEP is present.

Note that until the introduction of Platform -Security FEPs were implemented as polymorphic DLLs. Significantly, -under Platsec, FEPs require a capability of All - Tcb as they may be -loaded by any application.

Description

The API has five key concepts: FEP -base, control input capability, FEP-aware text editor, foreground observer -and focus observer.

FEP Base

The FEP -base, CCoeFep, is the abstract base class from which a -FEP is derived. A FEP is typically implemented to have a window owning control, -the standard Symbian OS means of receiving input events. The UI Control Framework -uses a control stack to determine the order in which controls are offered -key events. A FEP places its control on the stack with a high priority such -that it has first access to key events.

- FEP Base - -

The Window Server provides support for windows that float above -other windows in the application. This allows a FEP to have a visible presence.

Each -running application has its own instance of the current FEP. Support is provided -for synchronising attributes across all instances so that there appears to -be only one.

Control input-capabilities

A FEP must -be able to discover the input-capabilities of the target control(s) to determine -what output is appropriate. Input capabilities are provided by TCoeInputCapabilities.

FEP-aware -text editors

A text-editing control can be designed to be closely -integrated with a FEP by implementing MCoeFepAwareTextEditor. -Most of the Symbian provided editing controls do this. The use of in-line -editing in FEP aware editors can mean that a FEP has no obvious visible presence -at all.

Foreground observer

A FEP can implement an -observer interface to be notified when the application goes into the foreground -or background. The foreground observer is MCoeForegroundObserver.

Focus -observer

A FEP can implement an observer to be notified when controls -under the FEP gain or lose focus. The FEP can then discover the input-capabilities -of the current target control(s). The focus observer is MCoeFocusObserver.