WP7: Canvas controls from xaml can be null?

[Radu Stefan]

In MainPage.xaml I have 2 canvas controls (bd1 and ball) that represent 2 layers.

<Canvas  x:Name="ContentCanvas" Width="354" Height="669">
                <Canvas.Background>
                        <RadialGradientBrush>
                            <GradientStop Color="#FF9D0A0A" Offset="0" />
                            <GradientStop Color="Black" Offset="1" />
                        </RadialGradientBrush>
                </Canvas.Background>
                <Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
                            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
                            x:Name="bd1" Width="370" Height="480" Clip="F1 M 0,0L 640,0L 640,480L 0,480L 0,0" MouseMove="Canvas_MouseMove" HorizontalAlignment="Left" VerticalAlignment="Top">
                        <Canvas.RenderTransform>
                            <TransformGroup>
                                <RotateTransform Angle="0" CenterX="0.5" CenterY="0.5" />
                                <TranslateTransform X="0" Y="0" />
                                <ScaleTransform ScaleX="1" ScaleY="1" />
                                <SkewTransform AngleX="0" AngleY="0"/>
                            </TransformGroup>
                        </Canvas.RenderTransform>
                        <Path....../>
                        ........
                </Canvas>
                <Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
                            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Name="ball" 
                            Width="54" Height="52.5" Clip="F1 M 0,0L 54,0L 54,52.5L 0,52.5L 0,0"
                             MouseMove="Canvas_MouseMove" HorizontalAlignment="Left" VerticalAlignment="Top">
                        <Canvas.RenderTransform>
                            <TransformGroup>
                                <RotateTransform Angle="0" CenterX="0.5" CenterY="0.5" />
                                <TranslateTransform X="0" Y="0" />
                                <ScaleTransform ScaleX="1" ScaleY="1" />
                                <SkewTransform AngleX="0" AngleY="0"/>
                            </TransformGroup>
                        </Canvas.RenderTransform>
                        <Canvas Width="640" Height="480.425" Canvas.Left="0" Canvas.Top="0">
                            <Ellipse x:Name="Ellipse" Width="54" Height="52.5" Canvas.Left="4.17233e-007" Canvas.Top="2.03252e-005" Stretch="Fill" StrokeLineJoin="Round" Stroke="#FFFF0000">
                                <Ellipse.Fill>
                                    <LinearGradientBrush StartPoint="0.0633299,0.762378" EndPoint="0.93667,0.237621">
                                        <LinearGradientBrush.GradientStops>
                                            <GradientStop Color="#FF000000" Offset="0"/>
                                            <GradientStop Color="#FFFFFFFF" Offset="1"/>
                                        </LinearGradientBrush.GradientStops>
                                    </LinearGradientBrush>
                                </Ellipse.Fill>
                            </Ellipse>
                        </Canvas>
                    </Canvas>

For that I created a class called Layer that has a Canvas property :

public class Layer
        {
                public Layer() { }
                public Layer(Canvas canvas, Tipologie tip) 
                {
                    ThisCanvas = canvas; Tip = tip;
                }
                public string Name { get; set; }  
                private Canvas canv;
                public Canvas ThisCanvas
                {
                    get { return canv; }
                    set
                    {                
                        canv = value;
                        if (value != null)                        
                            Name = value.GetValue(Canvas.NameProperty) as string;
                    }
                }
        }

In the MainPage class I have a global collection of Layer type. Initially I put in the collection 2 layers.

private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
        {
            Layers[0] = new Layer(); Layers[0].ThisCanvas = GetTemplateChild("bd1") as Canvas;
            Layers[1] = new Layer(); Layers[1].ThisCanvas = ball;
            LayerSelector.ItemsSource = Layers;
        } 
        Layer[] Layers = new Layer[2];

The problem is that bd1 and ball canvas controls are null . I also tried to put the code in the constructor of the page but it was the same problem.

I can't explain that.

Am I doing something wrong? Thanks in advance!