Silverlight 3 - Data Binding Position of a rectangle on a canvas

Question

Hi Everyone,

I am currently trying to bind a collection of objects to a Canvas in Silverlight 3 using an ItemsControl as below:

<ItemsControl x:Name="ctrl" ItemsSource="{Binding myObjectsCollection}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <Canvas></Canvas>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Rectangle Stroke="LightGray" Fill="Black"  StrokeThickness="2" 
                   RadiusX="15" RadiusY="15" Canvas.Left="{Binding XAxis}"
                   Height="25" Width="25">
            </Rectangle>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

Unfortunately it seems the binding on the Canvas.Left is being ignored. From what i have learned here it would appear this is due to the items being placed inside a content presenter not the actual canvas i have specified in the items panel.

Is there a way i can use data binding to determine the position of elements on a canvas?

Answer 1

You are right, a ContentPresenter is inserted between the Canvas and the Rectangle. One workaround would be to set a left margin instead of a Canvas.Left:

<Rectangle Stroke="LightGray" Fill="Black" StrokeThickness="2" 
      RadiusX="15" RadiusY="15" Height="25" Width="25">
    <Rectangle.Margin>
        <Thickness Left="{Binding XAxis}"/>
    </Rectangle.Margin>
</Rectangle>

Answer 2

I realize that this already has an answer accepted, but the way to achieve the initial goal without messing with margins is to create a custom ItemsControl and override the PrepareContainerForItemOverride method. In this method, you set the binding in code.

public class CustomItemsCollection
    : ItemsControl
{
    protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
    {

        FrameworkElement contentitem = element as FrameworkElement;
        Binding leftBinding = new Binding("Left"); // "Left" is the property path that you want to bind the value to.
        contentitem.SetBinding(Canvas.LeftProperty, leftBinding);

        base.PrepareContainerForItemOverride(element, item);
    }

}

Answer 3

Add the following to your ItemsControl

 <ItemsControl.ItemContainerStyle>
    <Style TargetType="{x:Type ContentPresenter}">
      <Setter Property="Canvas.Left" Value="{Binding XPath=XAxis}"/>
    </Style>
  </ItemsControl.ItemContainerStyle>

No need for any custom controls

Answer 4

You cannot use ItemsControl.ItemContainerStyle in Silverlight. It doesn't exist. It exists only on a couple of leaf level classes like ListBox itself.