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PODependency Property in User Control works only on the first instance
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  1. PODependency Property in User Control works only on the first instance
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    copied!<p>I have several custom user controls in a window. They appear dynamically, like workspaces. I need to add a dependency property on an itemscontrol to trigger a scrolldown when an item is being added to the bound observable collection to my itemscontrol, like so: (usercontrol)</p> <pre><code>&lt;ScrollViewer VerticalScrollBarVisibility="Auto" &gt; &lt;ItemsControl Grid.Row="0" ItemsSource="{Binding Messages}" View:ItemsControlBehavior.ScrollOnNewItem="True"&gt; &lt;ItemsControl.ItemTemplate&gt; &lt;DataTemplate&gt; &lt;TextBox IsReadOnly="True" TextWrapping="Wrap" Text="{Binding Path=DataContext, RelativeSource={RelativeSource Self}}" /&gt; &lt;/DataTemplate&gt; &lt;/ItemsControl.ItemTemplate&gt; &lt;/ItemsControl&gt; &lt;/ScrollViewer&gt; </code></pre> <p>And the code of my dependency property : </p> <pre><code> public class ItemsControlBehavior { static readonly Dictionary&lt;ItemsControl, Capture&gt; Associations = new Dictionary&lt;ItemsControl, Capture&gt;(); public static bool GetScrollOnNewItem(DependencyObject obj) { return (bool)obj.GetValue(ScrollOnNewItemProperty); } public static void SetScrollOnNewItem(DependencyObject obj, bool value) { obj.SetValue(ScrollOnNewItemProperty, value); } public static readonly DependencyProperty ScrollOnNewItemProperty = DependencyProperty.RegisterAttached( "ScrollOnNewItem", typeof(bool), typeof(ItemsControl), new UIPropertyMetadata(false, OnScrollOnNewItemChanged)); public static void OnScrollOnNewItemChanged( DependencyObject d, DependencyPropertyChangedEventArgs e) { var mycontrol = d as ItemsControl; if (mycontrol == null) return; bool newValue = (bool)e.NewValue; if (newValue) { mycontrol.Loaded += new RoutedEventHandler(MyControl_Loaded); mycontrol.Unloaded += new RoutedEventHandler(MyControl_Unloaded); } else { mycontrol.Loaded -= MyControl_Loaded; mycontrol.Unloaded -= MyControl_Unloaded; if (Associations.ContainsKey(mycontrol)) Associations[mycontrol].Dispose(); } } static void MyControl_Unloaded(object sender, RoutedEventArgs e) { var mycontrol = (ItemsControl)sender; Associations[mycontrol].Dispose(); mycontrol.Unloaded -= MyControl_Unloaded; } static void MyControl_Loaded(object sender, RoutedEventArgs e) { var mycontrol = (ItemsControl)sender; var incc = mycontrol.Items as INotifyCollectionChanged; if (incc == null) return; mycontrol.Loaded -= MyControl_Loaded; Associations[mycontrol] = new Capture(mycontrol); } class Capture : IDisposable { public ItemsControl mycontrol{ get; set; } public INotifyCollectionChanged incc { get; set; } public Capture(ItemsControl mycontrol) { this.mycontrol = mycontrol; incc = mycontrol.ItemsSource as INotifyCollectionChanged; incc.CollectionChanged +=incc_CollectionChanged; } void incc_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { if (e.Action == NotifyCollectionChangedAction.Add) { ScrollViewer sv = mycontrol.Parent as ScrollViewer; sv.ScrollToBottom(); } } public void Dispose() { incc.CollectionChanged -= incc_CollectionChanged; } } } </code></pre> <p>During the first instantiation of my user control, it works like a charm. But when another user control of the same type is dynamically instantiated, the DependencyProperty is never attached anymore to my scrollviewer. Only the first instance will work correctly. I know that dependency properties are static, but does that mean they can't work at the same time on several user control of the same type added to the window? </p> <p>Update 02/03 : Here's how I set the viewmodel to the view (not programmatically) : </p> <pre><code> &lt;ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:vm="clr-namespace:testDp.ViewModel" xmlns:View="clr-namespace:testDp.View"&gt; &lt;DataTemplate DataType="{x:Type vm:ChatTabViewModel}"&gt; &lt;View:ChatTabView /&gt; &lt;/DataTemplate&gt; &lt;/ResourceDictionary&gt; </code></pre> <p>even with x:shared = false in the datatemplate tag, it won't work. But if I set the datacontext in a classic way like usercontrol.datacontext = new viewmodel(), it definitely work. But it's recommended to have a "shared" view, so how do we make dependency properties work with this "xaml" way of setting datacontext ?</p>
 

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