Restoring Bindings after XamlReader parsing - wpf

Question

my problem is the following: In my program I let the user place shapes (class DrawingShape) on a Canvas. The Drawing Shape encapsulates a stacked path and label:
<UserControl x:Class="HandballTrainerFluent.Graphics.DrawingShape"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="60"
d:DesignWidth="60"
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid x:Name="container" Width="Auto" Height="Auto">
<Grid.RowDefinitions>
<RowDefinition Height="38"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Canvas x:Name="geometryCanvas" HorizontalAlignment="Center" Grid.Row="0" Width="38" Height="38">
<Path x:Name="Path"
Width="35.8774"
Height="31.2047"
Canvas.Left="1.0613"
Canvas.Top="3.29528"
Stretch="Fill"
StrokeLineJoin="Round"
Stroke="{Binding OutlineBrush,Mode=OneWay}"
StrokeThickness="{Binding OutlineWidth,Mode=OneWay}"
StrokeDashArray="{Binding OutlinePattern,Mode=OneWay}"
Fill="{Binding FillBrush,Mode=OneWay}"
Data="F1 M 19,3.79528L 1.5613,34L 36.4387,34L 19,3.79528 Z "/>
</Canvas>
<TextBlock x:Name="TextBox" HorizontalAlignment="Center" Grid.Row="1" Text="{Binding LabelText,Mode=OneWay}"></TextBlock>
</Grid>
</UserControl>
So some visual setting and the label text are bound to Properties of the code-behind file.
After deserializing a Canvas with these Drawing shapes, I need to restore the binding between the XAML and the code-behind file. I've tried this, but it does not seem to work:
private void RepairBindingsAfterLoading()
{
foreach (UIElement element in this.drawingCanvas.Children)
{
if (element.GetType() == typeof(DrawingShape))
{
DrawingShape shape = (DrawingShape)element;
BindingOperations.ClearAllBindings(shape.Path);
BindingOperations.ClearAllBindings(shape.TextBox);
BindingOperations.ClearAllBindings(shape);
shape.BeginInit();
Binding dataContextBinding = new Binding();
dataContextBinding.RelativeSource = RelativeSource.Self;
shape.SetBinding(DrawingShape.DataContextProperty, dataContextBinding);
Binding fillBinding = new Binding("FillBrush");
shape.Path.SetBinding(Path.FillProperty, fillBinding);
Binding outlineBinding = new Binding("OutlineBrush");
shape.Path.SetBinding(Path.StrokeProperty, outlineBinding);
Binding widthBinding = new Binding("OutlineWidth");
shape.Path.SetBinding(Path.StrokeThicknessProperty, widthBinding);
Binding patternBinding = new Binding("OutlinePattern");
shape.Path.SetBinding(Path.StrokeDashArrayProperty, patternBinding);
Binding labelTextBinding = new Binding("LabelText");
shape.TextBox.SetBinding(TextBlock.TextProperty, labelTextBinding);
shape.EndInit();
shape.UpdateLayout();
}
}
}
No matter what I do to the code-behind Properties (e.g. change FillBrush), the visuals of the displayed DrawingShape won't update. Am I missing an important step here?
I've added shape.BeginUpdate() and shape.EndUpdate() after seeing this question: Bindings not applied to dynamically-loaded xaml
Thanks a lot for any insights
Edit 2012-09-25
Looking at another piece of code which does not depend on any bindings makes me wonder, if I can actually reference any elements from the Xaml-Definition via their x:Name after de-serialization. The following callback does not do anything on a shape:
private void rotateClockwiseMenuItem_Click(object sender, RoutedEventArgs e)
{
if(this.drawingCanvas.SelectedItem.GetType() == typeof(DrawingShape))
{
DrawingShape shape = (DrawingShape)this.drawingCanvas.SelectedItem;
TransformGroup transformStack = new TransformGroup();
transformStack.Children.Add(shape.geometryCanvas.LayoutTransform);
transformStack.Children.Add(new RotateTransform(90));
shape.geometryCanvas.LayoutTransform = transformStack;
}
}
Debugging tells me that the contents of shape seem just right. When I execute the command once, shape.geometryCanvas.LayoutTransformis the identity matrix. When executing it a second time, shape.geometryCanvas.LayoutTransform is a TransformGroup of two elements.
It somehow looks like the reference for geometryCanvas (declared in the Xaml) is no the one used on screen.

Answer 1

Got it!
I didn't know that you can't successfully reference x:Name'd XAML elements from outside the code-behind file after de-serialization (that at least seems to be the problem at hand).
A solution is to use FindName() on the UserControl, e.g.:
TextBlock textBox = shape.FindName("TextBox") as TextBlock;
The complete and correct RepairBindingsAfterLoading() looks like this:
private void RepairBindingsAfterLoading()
{
foreach (UIElement element in this.drawingCanvas.Children)
{
if (element.GetType() == typeof(DrawingShape))
{
DrawingShape shape = (DrawingShape)element;
shape.DataContext = shape;
Path path = shape.FindName("Path") as Path;
Binding fillBinding = new Binding("FillBrush");
path.SetBinding(Path.FillProperty, fillBinding);
Binding outlineBinding = new Binding("OutlineBrush");
path.SetBinding(Path.StrokeProperty, outlineBinding);
Binding widthBinding = new Binding("OutlineWidth");
path.SetBinding(Path.StrokeThicknessProperty, widthBinding);
Binding patternBinding = new Binding("OutlinePattern");
path.SetBinding(Path.StrokeDashArrayProperty, patternBinding);
TextBlock textBox = shape.FindName("TextBox") as TextBlock;
Binding labelTextBinding = new Binding("LabelText");
textBox.SetBinding(TextBlock.TextProperty, labelTextBinding);
}
}
}
Just for the record, my clumsy
BindingOperations.ClearAllBindings(shape.Path);
BindingOperations.ClearAllBindings(shape.TextBox);
BindingOperations.ClearAllBindings(shape);
works just like the much more simple and elegant solution suggested by dbaseman with:
shape.DataContext = this;
Hope this helps someone else to avoid my mistake :-)