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<concept id="GUID-FCEDC338-61CA-5D10-A8DB-E44A3EBBDE5E" xml:lang="en"><title>Front

End Processor Overview</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-4DBE2888-BC56-417E-B12F-520A9AFF5CBE"><title>Purpose</title> <p>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. </p> </section>

<section id="GUID-CB4AD573-8695-4BE0-A40D-DCB813AD313C"><title>Architectural relationships</title> <p>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. </p> <p>Note that until the introduction of <xref href="GUID-4BFEDD79-9502-526A-BA7B-97550A6F0601.dita">Platform

Security</xref> FEPs were implemented as polymorphic DLLs. Significantly,

under Platsec, FEPs require a capability of <b>All - Tcb</b> as they may be

loaded by any application. </p> </section>

<section id="GUID-DDA8FA60-B059-45ED-98FE-BA0C274BFC36"><title>Description</title> <p>The API has five key concepts: FEP

base, control input capability, FEP-aware text editor, foreground observer

and focus observer. </p> <p><b>FEP Base</b> </p> <p>The FEP

base, <xref href="GUID-ADAA039A-7BF3-3B06-8486-2E3604C2633D.dita"><apiname>CCoeFep</apiname></xref>, 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. </p> <fig id="GUID-55FA95ED-227B-560E-98B4-CCFB8E42A216">

<title>                 FEP Base               </title>

<image href="GUID-DD3A519B-26D5-5920-BEF3-16273A661448_d0e16898_href.png" placement="inline"/>

</fig> <p>The Window Server provides support for windows that float above

other windows in the application. This allows a FEP to have a visible presence. </p> <p>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. </p> <p><b>Control input-capabilities</b> </p> <p>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 <xref href="GUID-BB7D0D56-1713-3DC0-BDA0-3CA1F0462BE2.dita"><apiname>TCoeInputCapabilities</apiname></xref>. </p> <p><b>FEP-aware

text editors</b> </p> <p>A text-editing control can be designed to be closely

integrated with a FEP by implementing <xref href="GUID-A5D563D6-A99A-31DF-B844-5F94EF5FFE87.dita"><apiname>MCoeFepAwareTextEditor</apiname></xref>.

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. </p> <p><b>Foreground observer</b> </p> <p>A FEP can implement an

observer interface to be notified when the application goes into the foreground

or background. The foreground observer is <xref href="GUID-2CAC79B0-8BD3-3961-A162-75B004AEE5FC.dita"><apiname>MCoeForegroundObserver</apiname></xref>. </p> <p><b>Focus

observer</b> </p> <p>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 <xref href="GUID-E591B7D7-ED56-3CEF-883F-7091D5833731.dita"><apiname>MCoeFocusObserver</apiname></xref>. </p> </section>

<section id="GUID-90026D68-1FB6-4190-B0A8-9CDD0B1C6C18"><title>See also</title> <p><xref href="GUID-37E8A48E-09B8-5958-9263-B33EDAE3F7C6.dita">UI

Control Framework Overview</xref>  </p> </section>

</conbody></concept>