Question

I’m trying to use a MultiBinding as the ItemsSource for a ListBox, and I want to bind a couple of collections to the MultiBinding. The collections aren’t populated until after the host control (a derivation of Page) has already been instantiated. Just after being constructed, I call a method that sets up some of the data for the Page, including these collections.

Right now, I have something like this:

public void Setup() {     var items = MyObject.GetWithID(backingData.ID); // executes a db query to populate collection       var relatedItems = OtherObject.GetWithID(backingData.ID); } 

and I want to do something like this in XAML:

<Page ...    ...      <ListBox>         <ListBox.ItemsSource>             <MultiBinding Converter='{StaticResource converter}'>                 <Binding Source='{somehow get items}'/>                 <Binding Source='{somehow get relatedItems}'/>             </MultiBinding>         </ListBox.ItemsSource>     </ListBox>   ... </Page> 

I know I can’t use DynamicResource in a Binding, so what can I do?

Answer 1

Sounds to me like what you really want is a CompositeCollection and to setup a DataContext for your Page.

<Page x:Class='MyPage' DataContext='{Binding RelativeSource={RelativeSource Self}}'>     <Page.Resources>         <CollectionViewSource Source='{Binding Items}' x:Key='items' />         <CollectionViewSource Source='{Binding RelatedItems}' x:Key='relatedItems' />     </Page.Resources>      <ListBox>        <ListBox.ItemsSource>          <CompositeCollection>            <CollectionContainer              Collection='{StaticResource items}' />            <CollectionContainer              Collection='{StaticResource relatedItems}' />          </CompositeCollection>        </ListBox.ItemsSource>     </ListBox> </Page> 

The Code behind would look something like this:

public class MyPage : Page {     private void Setup()     {         Items = ...;         RelatedItems = ...;     }      public static readonly DependencyProperty ItemsProperty =         DependencyProperty.Register('Items', typeof(ReadOnlyCollection<data>), typeof(MyPage),new PropertyMetadata(false));     public ReadOnlyCollection<data> Items     {         get { return (ReadOnlyCollection<data>)this.GetValue(ItemsProperty ); }         set { this.SetValue(ItemsProperty , value); }      }      public static readonly DependencyProperty RelatedItemsProperty =         DependencyProperty.Register('RelatedItems', typeof(ReadOnlyCollection<data>), typeof(MyPage),new PropertyMetadata(false));     public ReadOnlyCollection<data> RelatedItems     {         get { return (ReadOnlyCollection<data>)this.GetValue(RelatedItemsProperty ); }         set { this.SetValue(RelatedItemsProperty , value); }      } } 

Edit: I remembered that CollectionContainer doesn’t participate in the logical tree so you need to use a CollectionViewSource and a StaticResource.