Programmatically Create Grid with Custom Element

I'm trying to create a grid programmatically and appending a custom control as a child to the grid as row 0 column 0 out of a 2x2 matrix. To make matters more tricky, I'm using the MVVM design pattern. Heres some code to help everyone get the idea:

App.xaml.cs

base.OnStartup(e);
var viewModel = new MainWindowViewModel();
var mainWindow = new MainWindow();
mainWindow.GridWindows = viewModel.Window.GridWindows;

MainWindowViewModel - method returns the GridWindows.

    private Grid CreateGrid()
    {
        Grid grid = new Grid();

        // Create column definitions.
        ColumnDefinition columnDefinition1 = new ColumnDefinition();
        ColumnDefinition columnDefinition2 = new ColumnDefinition();
        columnDefinition1.Width = new GridLength(640);
        columnDefinition2.Width = new GridLength(640);

        // Create row definitions.
        RowDefinition rowDefinition1 = new RowDefinition();
        RowDefinition rowDefinition2 = new RowDefinition();
        rowDefinition1.Height = new GridLength(340);
        rowDefinition2.Height = new GridLength(340);

        // Attached definitions to grid.
        grid.ColumnDefinitions.Add(columnDefinition1);
        grid.ColumnDefinitions.Add(columnDefinition2);
        grid.RowDefinitions.Add(rowDefinition1);
        grid.RowDefinitions.Add(rowDefinition2);

        // Create preview window.
        Border border = new Border();
        border.BorderThickness = new Thickness(20);
        border.Padding = new Thickness(8);
        border.SetResourceReference(Control.BackgroundProperty, "PreviewWindow");

        MediaRTSPElement previewElement = new MediaRTSPElement();
        previewElement.Name = "RTSPStreamPlayer";
        previewElement.Stretch = Stretch.UniformToFill;
        previewElement.Source = "rtsp://192.100.100.22/media/video1";
        previewElement.VideoRenderer = VideoRendererType.EnhancedVideoRenderer;
        previewElement.LoadedBehavior = WPFEVR.DirectShow.Players.MediaState.Play;
        previewElement.SpeedRatio = 0.5;

        //border.Child = previewElem开发者_Go百科ent;

        // Add preview window.
        for (int i = 0; i < 4; i++)
        {
            grid.Children.Add(previewElement as UIElement);
            Grid.SetColumn(previewElement, i);
            Grid.SetRow(previewElement, i);
            break;
        }

        return grid;
    }

And the XAML Markup that the grid should assign to

<Grid x:Name="GridWindows"></Grid>

The problem is my custom control does not appear in the grid layout, heres the xaml code that does it without code-behind, and this does work:

        <Grid x:Name="GridWindows">
            <!--<Grid.ColumnDefinitions>
                <ColumnDefinition Width="640" />
                <ColumnDefinition Width="640" />
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="340" />
                <RowDefinition Height="340" />
            </Grid.RowDefinitions>
            <Border BorderThickness="20" Padding="8" Background="{DynamicResource ResourceKey=PreviewWindow}" Grid.Row="0" Grid.Column="0">
                <evr:MediaRTSPElement x:Name="RTSPStreamPlayer"
                              Stretch="UniformToFill"
                              VideoRenderer="EnhancedVideoRenderer"
                              LoadedBehavior="Play"
                              Source="rtsp://192.100.100.22/media/video1"
                              SpeedRatio="0.5" />
            </Border>
            <Border BorderThickness="20" Padding="8" Background="{DynamicResource ResourceKey=PreviewWindow}" Grid.Row="0" Grid.Column="1">
                <evr:MediaRTSPElement x:Name="RTSPStreamPlayer2"
                              Stretch="UniformToFill"
                              VideoRenderer="EnhancedVideoRenderer"
                              LoadedBehavior="Play"
                              Source="rtsp://192.100.100.78/media/video1"
                              SpeedRatio="0.5" />
            </Border>
            <Border BorderThickness="20" Padding="8" Background="{DynamicResource ResourceKey=PreviewWindow}" Grid.Row="1" Grid.Column="0">
                <evr:MediaRTSPElement x:Name="RTSPStreamPlayer3"
                              Stretch="UniformToFill"
                              VideoRenderer="EnhancedVideoRenderer"
                              LoadedBehavior="Play"
                              Source="rtsp://192.100.100.78/media/video1"
                              SpeedRatio="0.5" />
            </Border>
            <Border BorderThickness="20" Padding="8" Background="{DynamicResource ResourceKey=PreviewWindow}" Grid.Row="1" Grid.Column="1">
                <evr:MediaRTSPElement x:Name="RTSPStreamPlayer4"
                              Stretch="UniformToFill"
                              VideoRenderer="EnhancedVideoRenderer"
                              LoadedBehavior="Play"
                              Source="rtsp://192.100.100.22/media/video1"
                              SpeedRatio="0.5" />
            </Border>-->
        </Grid>

Any ideas as to why programmatic code isn't working?

if you're creating Grid in the xaml you can't later set it in code. Grid (instance) is already in visualtree. Overwriting variable won't do any effect. You should set your Grid as content of xaml defined control. I'm guessing that your code looks like this:

Code:

this.GridWindows = createdGrid;

Xaml:

<Grid x:Name="GridWindows"></Grid>

In code you should have something like this:

this.GridWindows.Children.Add(createdGrid);