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POCombo-box loses selection after collection changes
 

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    <p>I have a WPF combo box bound to an obvserable collection (OC):</p> <pre><code> &lt;ComboBox Name="cbCombination" ItemsSource="{Binding Combinations}" SelectedIndex="0" /&gt; </code></pre> <p>Elsewhere, in the object set as data context:</p> <pre><code> public ObservableCollection&lt;Combination&gt; Combinations { get; set; } </code></pre> <p>Combination overrides its ToString and everything is peachy: The combo-box's drop-down displays all Combination items in the Combinations OC. The combo-box's selection box displays the value of the first Combination.</p> <p>Now, the data-context object has to change the values in its Combinations OC:</p> <pre><code> var combinationsList = CombinationsManager.CombinationsFor(someParam); this.Combinations.Clear(); foreach (var combination in combinationsList) this.Combinations.Add(combination); NotifyPropertyChanged(@"Combinations"); </code></pre> <p>This causes the combo-box's selection box shows an empty string. (The drop-down is closed. However, when I make it drop down, it does show the correct new Combinations, so it <em>is</em> bound to the updated collection).</p> <p>I tried to capture both SourceUpdated and (in my dispair) TargetUpdated events (thining of setting the SelectedIndex there), but my event handlers didn't get called!</p> <p>So my question is: <strong>How do I make a WPF ComboBox refresh the value of its selection-box when the observable collection it is bound-to changes?</strong></p> <p><strong>Update</strong>: </p> <p>I've totally forgotten to mention, and I don't know whether it's important, but the combo-box is within a UserControl. The UserControl's XAML looks like this:</p> <pre><code>&lt;UserControl x:Class="...CombinationsToolBar" .... mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="300"&gt; &lt;ToolBarTray Name="toolBarTray1" &gt; &lt;ToolBar Name="toolBar1"&gt; &lt;ComboBox Name="cbCombination" ItemsSource="{Binding Path=Combinations, NotifyOnSourceUpdated=True, IsAsync=True}" SelectedIndex="0" IsEditable="False" SelectionChanged="CbCombinationSelectionChanged" SourceUpdated="CbCombinationSourceUpdated" TargetUpdated="CbCombinationTargetUpdated"&gt;&lt;/ComboBox&gt; &lt;/ToolBar&gt; &lt;/ToolBarTray&gt; </code></pre> <p></p> <p><strong>In the UserControl's code</strong> I have breakpoints on CbCombinationSelectionChanged, CbCombinationSourceUpdated and CbCombinationTargetUpdated. </p> <p>The CbCombinationSelectionChanged fires once when the form containing the user control is first loaded. It is indeed called a second time when the Combinations collection is cleared, as @asktomsk said.</p> <p>The source updated and target updated are not triggered - CbCombinationSourceUpdated and CbCombinationTargetUpdated are not called. </p> <p>As the combo box is inside a usercontrol and the Combinations collection is within the view model, and as the view model doesn't have access to the combo box, <strong>I have no opportunity to set the selected index of the combo unless the events fire</strong>.</p> <p>:(</p>
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