Question

I’m using the lastest version of Silverlight 2.0 within Visual Studio 2008. I have a simple Silverlight UserControl with the following code:

public partial class SilverlightControl1 : UserControl
{
    public SilverlightControl1()
    {
        InitializeComponent();
        this.Loaded += new RoutedEventHandler(SilverlightControl1_Loaded);
        Composite = new Composite();
    }

    void SilverlightControl1_Loaded(object sender, RoutedEventArgs e)
    {
        Composite.Width = this.Width / 2.0;
        Composite.Height = this.Height / 2.0;
        if (!this.LayoutRoot.Children.Contains(Composite)) 
            this.LayoutRoot.Children.Add(Composite);
    }

    public Composite Composite
    {
        get;
        set;
    }
}

public class Composite : ContentControl
{
    private Grid grid;
    private Canvas canvas;

    public Composite()
    {
        if (grid == null) grid = new Grid();
        if (canvas == null) canvas = new Canvas();
        if (!grid.Children.Contains(canvas)) 
            grid.Children.Add(canvas);
        Content = grid;
        this.Loaded += new RoutedEventHandler(Composite_Loaded);
    }

    private Rectangle rectangle;

    void Composite_Loaded(object sender, RoutedEventArgs e)
    {
        if (rectangle == null) rectangle = new Rectangle();
        Canvas.SetTop(rectangle, 0);
        Canvas.SetLeft(rectangle, 0);
        rectangle.Fill = new SolidColorBrush(Color);
        rectangle.Width = Width;
        rectangle.Height = Height;
        if (!canvas.Children.Contains(rectangle)) 
            canvas.Children.Add(rectangle);
    }

    public Color Color
    {
        get;
        set;
    }
}

I then use this UserControl in a Silverlight application, the XAML of the page looking like this:

<UserControl x:Class="SilverlightApplication1.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:test="clr-namespace:SilverlightClassLibrary1;assembly=SilverlightClassLibrary1"
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="Green">
    <test:SilverlightControl1 Name="uControl1">
      <test:SilverlightControl1.Composite>
        <test:Composite Color="Yellow"/>
      </test:SilverlightControl1.Composite>
    </test:SilverlightControl1>
    </Grid>
</UserControl>

My question is: what code do I have to add to the above so that by changing “Composite Color” to something other than Yellow and hitting the return button, the UserControl automatically refreshes? As the code is, the only way to refresh the UserControl is by moving the Slider bar within the VS2008 IDE which changes the percentage zoom of the Silverlight Page. A side question, although of lesser importance to the above question, is: with the code as it is above, why can’t I change the “Background” color of the LayoutRoot? If I remove my UserControl it works as expected.

Answer 1

The solution was two-fold. Firstly to make changes in the LayoutUpdated event rather than the Loaded event and secondly to subscribe to the PropertyChangedCallback of the PropertyMetadata. Here’s the complete working code:

  public partial class SilverlightControl1 : UserControl
  {
    public SilverlightControl1()
    {
      InitializeComponent();
      this.LayoutUpdated += new EventHandler(SilverlightControl1_LayoutUpdated);
      Composite = new Composite();
    }

    void SilverlightControl1_LayoutUpdated(object sender, EventArgs e)
    {
      Composite.Width = this.Width / 2.0;
      Composite.Height = this.Height / 2.0;
      if (!this.LayoutRoot.Children.Contains(Composite)) this.LayoutRoot.Children.Add(Composite);
    }

    public Composite Composite
    {
      get;
      set;
    }
  }

  public class Composite : ContentControl
  {
    private Grid grid;
    private Canvas canvas;

    public Composite()
    {
      if (grid == null) grid = new Grid();
      if (canvas == null) canvas = new Canvas();
      if (!grid.Children.Contains(canvas)) grid.Children.Add(canvas);
      Content = grid;
      this.LayoutUpdated += new EventHandler(Composite_LayoutUpdated);
    }

    void Composite_LayoutUpdated(object sender, EventArgs e)
    {
      if (rectangle == null) rectangle = new Rectangle();
      Canvas.SetTop(rectangle, 0);
      Canvas.SetLeft(rectangle, 0);
      rectangle.Fill = new SolidColorBrush(Color);

      rectangle.Width = Width;
      rectangle.Height = Height;
      if (!canvas.Children.Contains(rectangle)) canvas.Children.Add(rectangle);
    }

    public static readonly DependencyProperty ColorProperty = DependencyProperty.Register("Color", typeof(Color), typeof(Composite), new PropertyMetadata(Colors.Red, new PropertyChangedCallback(OnColorPropertyChanged)));

    private static void OnColorPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
      Composite comp = (Composite)d;
      comp.InvalidateArrange();
    }

    private Rectangle rectangle;

    public Color Color
    {
      get { return (Color)GetValue(ColorProperty); }
      set { SetValue(ColorProperty, value); }
    }
  }