No DataBinding when rendering a UserControl+ItemsControl in WriteableBitmap?

Question

I want to use a WriteableBitmap to render a programmatically instantiated UserControl to a jpg/png image to use it as a live tile background image in a Windows Phone 7.1 project, but DataBinding is not working as expected when rendering the control.

In general, the UserControl is something like this:

<UserControl>
  <Grid x:Name="LayoutRoot" Height="173" Width="173" >
    <Grid.Background >
      <SolidColorBrush Color="{StaticResource PhoneAccentColor}" />
    </Grid.Background >
    <Grid.RowDefinitions>
      <RowDefinition Height="27"/>
      <RowDefinition Height="146"/>
    </Grid.RowDefinitions >
    <ItemsControl Grid.Row="1" Margin="10,0,0,0" ItemsSource="{Binding}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <StackPanel />
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemTemplate>
          <DataTemplate>
            <TextBlock Text="{Binding MyBindingProperty, FallbackValue=xxx}" />
          </DataTemplate>
        </ItemsControl.ItemTemplate>
      </ItemsControl>
      <TextBlock Text="Hello World" FontSize="22" Margin="5,0,0,0"/>
      <TextBlock TextWrapping="Wrap" Text="{Binding Count, FallbackValue=-1}" FontSize="18.667" Margin="123,0,0,0"/>
    </Grid>
</UserControl>

When I now put this control onto a PhoneApplicationPage and assign a list with items of my data structure to the DataContext property of the UserControl, everything works fine and I see one TextBlock for each list item and the Text property of that TextBlock is correctly displaying the value of the property of my data structure. Also the last TextBlock on the Grid displays correctly the current count of list items.

BUT when I'm now trying to programmatically create that UserControl, assign the same list to the DataContext and then use a WriteableBitmap to render it to an image file, it seems that all DataBindings within the DataTemplate of the ItemsControl aren't working anymore, they're displaying the FallbackValue now. Although the DataBinding of the outer TextBlock in the Grid is still working perfectly and also I got the correct number of TextBlocks in the StackPanel (= items in the bound list).

Here is my code for creating the the WriteableBitmap:

var tile = new MyTileControl { DataContext = this._myList };
tile.Arrange(new Rect(0, 0, 173, 173));
tile.Measure(new Size(173, 173));

var bmp = new WriteableBitmap(173, 173); 
bmp.Render(tile, null); 
bmp.Invalidate();

What's the problem with the DataBindings in the DataTemplate when rendering through a WriteableBitmap and how can I solve it?

Ku6opr Ku6opr · Accepted Answer · 2011-12-25T10:05:49

I think, that your control not fully created yet, and you can't grab bitmap just after creation. Try to use Dispatcher.BeginInvoke or something else for delayed grabbing of image.

Also, add this control to your page and look where is a problem - in control creation or in bitmap? This give you more information about a problem.

No DataBinding when rendering a UserControl+ItemsControl in WriteableBitmap?

1 Answers