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<concept id="GUID-24039DCE-B5C4-46CB-9E02-AB421C64FB87" xml:lang="en"><title>Relationship

between window controls</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>When a control draws in the window of another control, the position

is relative to that window. If a control owns a window that is a child of

another window, that control's position is relative to the parent window;

however, if that control is a compound control, its child control's coordinates

are relative to its own parent control window position. Top-level window-owning

controls are displayed using a position relative to the display. In other

words, it uses the physical coordinates of the display.</p>

<p>The following figure illustrates this relationship.</p>

<fig id="GUID-9D373EB7-096D-4C84-8060-577F33D462EE"><title>Relative positions of three controls where the top-level parent owns

<p>Consider three controls, <b>A</b>, <b>B</b>, and <b>C</b> (shown in

the figure above):</p>

<ul>

<li><p><b>A</b> is a top-level control and owns a window</p>

</li>

<li><p>Child controls <b>B</b> and <b>C</b> do not create their

own windows in this example.</p></li>

<li><p><b>B</b>, a child control of <b>A</b>, does not create a

window, and it has a child control, <b>C</b>. </p>

<itemgroup>

<p><b>B</b>'s window is set calling the <parmname>CCoeControl::SetContainerWindowL(A)</parmname> method

and <b>C</b>'s window is set with <parmname>CCoeControl::SetContainerWindowL(B)</parmname>.

Then <b>C</b>'s position (p) is relative to <b>A</b>, since it is the actual

window owner. <b>A</b>'s position (m) is relative to the display position.</p>

</itemgroup>

</li>

</ul>

<p>However, if <b>B</b> is a child control of <b>A</b> but also has a window

of its own, it is a child window of <b>A</b>'s window (as shown in the following

figure). Then if <b>C</b> is a child of <b>B</b> and sets its window by calling <parmname>CCoeControl::SetContainerWindowL(B)</parmname>,

the position of <b>C</b> (p') is relative to <b>B</b>'s window.</p>

<p>As the example illustrates, a control position depends on the window

in which it is drawn. Therefore, you need to know the drawing window for each

control. It is an important issue when designing a UI layout. There are some

common controls that optionally may have their own window, such as menus,

dialogs, and scroll bars. The application framework handles drawing these

controls, as long as the appropriate resources and flags have been set. The <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-8AF77599-1FE4-36C1-AED8-1FB8A053354F"><apiname>CCoeControl::OwnsWindow()</apiname></xref> call

can be used to detect whether a control owns a window or not.</p>

</conbody></concept>