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POWPF: ICollectionView - Filter one list if item is contained in another list?
 

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  1. POWPF: ICollectionView - Filter one list if item is contained in another list?
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    <p>Basically, I have 2 ListView's each binding to a different <code>ItemsSource</code>.</p> <p>List 1 <b>can not</b> be changed (it's a <code>ReadOnlyObservableCollection</code>).<br /> List 2 <b>can</b> be changed (through user interaction).<br /></p> <p>I need to add a filter to List 1 so that it doesn't display anything that's found in List 2. This is my code so far...</p> <pre><code>view = CollectionViewSource.GetDefaultView(List1.ItemsSource); view.Filter += o =&gt; { MyItem item = o as MyItem; return List2.ItemsSource.??; }; </code></pre> <p><hr> List2.ItemsSource comes back as an IEnumerable instead of ObservableCollection (what it really is). I want to do this as efficiently as possible, so I wasn't sure if I should:</p> <ol> <li>Explicitly Cast the ItemsSource as a IList to gain access to Contains?</li> <li>Iterate through the the ItemsSource myself to see if it contains the item?</li> <li>Use LINQ's Cast extension method to cast to an IList (or some other type) to gain access to Contains?</li> <li>Any other way?</li> </ol> <hr> <p><b>UPDATE:</b></p> <p>It doesn't seem to continue filtering items after the first time it renders:</p> <pre><code>view = CollectionViewSource.GetDefaultView(List1.ItemsSource); view.Filter += o =&gt; { MyItem item = (MyItem)o; var collection = (ObservableCollection&lt;MyItem&gt;)List2.ItemsSource; //return collection.Contains(item);//Filters out ALL items from the list return !collection.Contains(item); //Shows all items, but as I add items //to list 2 it doesn't filter items out of //list 1. }; </code></pre> <p><b>UPDATE 2:</b></p> <p>I think I understand why it's not reapplying the filter. The original collection is not raising a CollectionChanged notification, so it doesn't bother to run the filter again. Perhaps solving this part is better suited as a different question? But, in case anyone wants to answer it here:</p> <p>How can I get my List1 to reapply the filter when the List2 collection changes?</p> <p><b>UPDATE 3:</b> I asked how to tie into the collectionchanged event in a <a href="https://stackoverflow.com/questions/5806172/wpf-how-do-i-hook-into-a-listviews-collectionchanged-notification">separate SO question</a> and got my answer.</p>
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