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<concept id="GUID-DAC32BB9-C0EB-42FF-A596-C2F1A90A4BD7" xml:lang="en"><title>Views</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The term <i>view</i> refers to the <xref href="GUID-BDDDF68F-F7C3-43AF-8B6C-C77C701FD2A9.dita">MVC

design</xref> (Model-View-Controller) component that has the following attributes:</p>

<ul>

<li><p>displays the application state known by the application</p>

</li>

<li><p>receives user input</p></li>

<li><p>is owned by the <xref href="GUID-FD2CDEB8-0784-4BE5-A775-170F57D71BBC.dita">UI

controller</xref></p></li>

<li><p>observes application state changes either directly or through

the UI controller and updates the screen accordingly</p></li>

</ul>

<p>In practice, views are collections of interface elements, such as controls,

menus, command button areas (CBAs), key events, that make up one top-level

window in an application. Applications may have one or more views. If an application

has more than one view and if the status pane behavior is organized in this

manner, then each view in an application can have its own tab. Applications

can have only a single view active at any one time. The current view is the

view that interacts with the user, receiving events and menu choices as if

it were the only set of UI elements.</p>

<p>Multiple view architectures are widely used in application development

on the Symbian platform. Multiple view architectures:</p>

<ul>

<li><p>provide developers with an efficient way to build multiple

views within an application and switch between them easily and simply. </p>

</li>

<li><p>allow applications to bundle their user interface requirements

into a single element (a view). The view architecture then provides the capability

to switch quickly between the views.</p></li>

<li><p>allow applications to take advantage of object orientation

to encapsulate code, keeping it simple and clear. </p></li>

<li><p>provide the ability for one application to activate the view

of another. This is particularly useful when you want to use an existing display

or editing capability without going to the expense of integrating a component

into your application. </p></li>

<li><p>allow applications to register views, with one view being

active in each running application at any one time. It does not dictate what

a view is; however, it does provide support for a view being a display page

on the screen</p></li>

</ul>

<fig id="GUID-79751C55-C0D9-4511-9147-8E6CB95AA610"><title>Controller-view hierarchy in traditional and Symbian architectures</title><image href="GUID-46040A24-92C3-4B0B-88CC-BDD8DDA8F27C_d0e41397_href.png"/></fig>

<p>In practice, the view concept varies depending upon your chosen architecture

approach: </p>

<section id="GUID-53125010-FFC7-422E-9EE5-A42427031F10"><title>Traditional architecture

views</title>

<p>In a traditional architecture, the view is derived from <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita"><apiname>CCoeControl</apiname></xref>,

which typically constructs a top-level window-owning control that draws itself

and contains other controls.</p>

<p>For more information on views in tradition architecture approaches,

see <xref href="GUID-B5DE1C86-2B16-4B22-887F-7079E54A8ED6.dita">Traditional

Symbian UI application architecture</xref>.</p>

</section>

<section id="GUID-B473202D-9682-4EBA-83F2-8391DB2B56D9"><title>Symbian architecture

views</title>

<p>In Symbian view architecture, a view controller is added between the <xref href="GUID-FD2CDEB8-0784-4BE5-A775-170F57D71BBC.dita">UI controller</xref> and

the view that draws itself and contains other controls. For example, view

controllers can be used to specify CBAs that are specific to specific views.</p>

<p>In a Symbian architecture, the view controller is derived from <xref href="GUID-11967EBB-7439-3775-B287-7560ECA0AF1F.dita"><apiname>CAknView</apiname></xref>,

which is derived directly from <xref href="GUID-8F6FE089-E2A8-30F4-B67E-10F286347681.dita"><apiname>CBase</apiname></xref> and not from <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita"><apiname>CCoeControl</apiname></xref>.

This means the <xref href="GUID-11967EBB-7439-3775-B287-7560ECA0AF1F.dita"><apiname>CAknView</apiname></xref>-derived views are not controls. <xref href="GUID-11967EBB-7439-3775-B287-7560ECA0AF1F.dita"><apiname>CAknView</apiname></xref>-derived

views need to contain <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita"><apiname>CCoeControl</apiname></xref>-derived classes to provide

visual representation on the display.</p>

<p>For more information on views in Symbian architecture approaches, see <xref href="GUID-68B999C2-0993-4804-9624-42C3D88BE5C7.dita">View

architecture</xref>.</p>

</section>

<section id="GUID-C9AA9483-424E-4626-8335-5F70FE246E1D"><title>Dialog architecture

views</title>

<p>In dialog architectures, views are implemented in modeless dialog boxes.

Multiple views can be constructed using nested dialogs or a tabbed dialog

pane.</p>

<p>For more information on views in dialog architecture approaches, see <xref href="GUID-DD88DD7B-E246-4BF2-B537-5C677728CC49.dita">Dialog

architecture</xref>.</p>

</section>