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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
the window</title><image href="GUID-61C340D0-9058-45C2-9A90-4AB8E0612872_d0e41032_href.png"/></fig>
<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>
<fig id="GUID-5884BDB6-6ED0-4EF6-A64F-3EEAAAEE2FF0"><title>Relative positions of three controls where a child owns a window</title><image href="GUID-3A506E2A-2999-458B-BBA2-DCC4D2EA5492_d0e41135_href.png"/></fig>
<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>