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

问题

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?

回答1:

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);
    }

}

回答2:

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

回答3:

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>

回答4:

I know this question is a little old, but you can just use a render transform - I'm doing something similar;

<ItemsControl ItemsSource="{Binding Notes}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <Canvas Background="Aqua"/>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>

    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border Width="{Binding W}" Height="{Binding H}" BorderBrush="Navy" BorderThickness="5" CornerRadius="10">
                <TextBlock Text="{Binding Text}"/>
                <Border.RenderTransform>
                    <TransformGroup>
                        <RotateTransform Angle="0"/>
                        <TranslateTransform X="{Binding X}" Y="{Binding Y}"/>
                    </TransformGroup>
                </Border.RenderTransform>
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

回答5:

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

来源：https://stackoverflow.com/questions/1637400/silverlight-3-data-binding-position-of-a-rectangle-on-a-canvas