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POWhy does ItemsControl show a focus rectangle when its parent is focused?
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  1. POWhy does ItemsControl show a focus rectangle when its parent is focused?
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    copied!<p>WPF's ItemsControl will display a focus rectangle when it thinks it has focus and the user presses Tab or Alt.</p> <p>But I recently had an ItemsControl display a focus rectangle even though it <em>did not have focus</em> -- one of its parents did. The ItemsControl was inside a UserControl, which was inside another UserControl that <em>did</em> have focus. Something like this:</p> <pre><code>&lt;!-- UserControl1.xaml; this is the control that has focus --&gt; &lt;UserControl x:Class="UserControl1" Focusable="True" ...&gt; &lt;UserControl2/&gt; &lt;/UserControl&gt; &lt;!-- UserControl2.xaml --&gt; &lt;UserControl x:Class="UserControl2"&gt; &lt;ItemsControl .../&gt; &lt;/UserControl&gt; </code></pre> <p>Or, to show the nesting visually:</p> <pre><code>+---------------------------------------------------+ | UserControl1 (has focus) | | | | +-----------------------------------------------+ | | | UserControl2 | | | | | | | | +-------------------------------------------+ | | | | | ItemsControl (shows focus rectangle) | | | </code></pre> <p>It took me a while (and a <a href="https://stackoverflow.com/questions/818566/remove-focus-rectangle-on-a-usercontrol">StackOverflow question</a>) to figure out where the focus rectangle was coming from, because I never expected a control that didn't have focus to show a focus rectangle.</p> <p>I'm still learning my way around WPF, and obviously I don't know enough yet, or this wouldn't have confused me. Two questions to help me understand:</p> <ol> <li><em>Why</em> does ItemsControl display a focus rectangle when it doesn't actually have focus, but one of its parent controls does? What's the reason for this feature? (I'm sure there is one -- maybe something to do with templates or visual trees? -- I just don't have a deep enough understanding of WPF mechanics and philosophy yet.)</li> <li><em>How</em> does this work? What's the mechanism ItemsControl uses to decide that it should display a focus rectangle?</li> </ol>
 

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