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copied!<p>With only your code mentioned above, it will be thrown as the null reference exception to write a collection property in XAML due to the fact from the <a href="http://msdn.microsoft.com/en-us/library/ms753379.aspx#Collection_Properties" rel="nofollow">MSDN</a>:</p> <pre><code>The presence of that collection type is implicit whenever you specify a property in XAML that takes a collection type. </code></pre> <p>So, I suggest initializing the collection in XAML as the following, if you do not want to have the collection instance in the class declaration.</p> <pre><code><Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:system="clr-namespace:System.Collections;assembly=mscorlib" xmlns:local="clr-namespace:WpfApplication1" Title="MainWindow" Height="350" Width="525"> <Window.Resources> <local:MiniObject x:Key="RootItem" Caption="Item0" Checked="True"> <local:MiniObject.Content> <system:ArrayList> -------------------------------------1) <local:MiniObject Caption="Item1" Checked="True"> </local:MiniObject> <local:MiniObject Caption="Item2" Checked="True"> </local:MiniObject> </system:ArrayList> </local:MiniObject.Content> </local:MiniObject> </Window.Resources> <Grid> <ListBox ItemsSource="{Binding Source={StaticResource ResourceKey=RootItem}, Path=Content}" DisplayMemberPath="Caption"/> </Grid> </Window> public class MiniObject { public bool Checked { get; set; } public String Caption { get; set; } public IList Content { get; set; } -----------------------------------------2) } </code></pre> <p>At the 2), you may know there are the four alternatives(IList,IDictionary, etc.) to be the collection property in XAML. Please, refer to the <a href="http://msdn.microsoft.com/en-us/library/ms753379.aspx#Collection_Properties" rel="nofollow">MSDN</a>. Above, ICollection is also OK, as the items are added to the ArrayList.</p> <p>At the 1), We cannot declare a generic type collection yet, but I know it would be supported as soon.</p>

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