WPF binding with custom control

Question

I am currently designing a system, (my first in WPF) and i am looking to bind properties of my custom control to elements set within the control-style.

<Style TargetType="{x:Type c:Connection}">
    <Setter Property="SnapsToDevicePixels" Value="true"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type c:Connection}">
                <Grid DataContext="{Binding RelativeSource={RelativeSource TemplatedParent}}">
                    <Line Stroke="Red" X1="90" X2="90" Y1="90" Y2="5"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

I am looking to bind the elements of the Line (X1/2 Y1/2) to properties within my Connection Control. However, as soon as i add a connection element (in code, even without binding), i get a Type Initialization Error. My Connection class is as follows:

public class Connection : Control
{
    public Connector StartElement { get; set; }
    public Connector EndElement { get; set; }

   #region Properties


    #endregion

}

And I Initialize as follows: Connection con = new Connection(); (and then i add it to the canvas).

How can i bind the coordinates to a the Points that are in Connector? (ex StartElement.GetXPosition());

Kind Regards Tom

What's the exact error are you getting, what location in your code is causing the error? It would help if you included your initialization code. — Rachel
– Rachel, Commented Mar 25, 2013 at 16:50

Viv · Accepted Answer · 2013-03-25 17:00:58Z

Are you sure your creating your elements correctly?

This works for me:

In Connection.cs file

using System.Windows.Controls;

public class Connector {
  public int X { get; set; }
  public int Y { get; set; }
}

public class Connection : Control {
  public Connector StartElement { get; set; }
  public Connector EndElement { get; set; }
}

Xaml:

<UserControl x:Class="WpfApplication1.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WpfApplication1">
  <UserControl.Resources>
    <Style TargetType="{x:Type local:Connection}">
      <Setter Property="SnapsToDevicePixels"
              Value="true" />
      <Setter Property="Template">
        <Setter.Value>
          <ControlTemplate TargetType="{x:Type local:Connection}">
            <Grid DataContext="{Binding RelativeSource={RelativeSource TemplatedParent}}">
              <Line Stroke="Red"
                    X1="{Binding StartElement.X}"
                    X2="{Binding EndElement.X}"
                    Y1="{Binding StartElement.Y}"
                    Y2="{Binding EndElement.Y}" />
            </Grid>
          </ControlTemplate>
        </Setter.Value>
      </Setter>
    </Style>
  </UserControl.Resources>
  <Canvas x:Name="canvasElement"
          Background="White" />
</UserControl>

and UserControl code-behind:

public UserControl1() {
  InitializeComponent();
  Connection connectionVariable = new Connection {
    StartElement = new Connector { X = 0, Y = 0 },
    EndElement = new Connector { X = 300, Y = 300 }
  };
  canvasElement.Children.Add(connectionVariable);
  Canvas.SetLeft(connectionVariable, 0);
  Canvas.SetTop(connectionVariable, 0);
}

Running this, I see a Red diagonal line.

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