WPF: Drawing canvas content to a bitmap problem

Question

I have a custom control of class DottedCanvas inherited from Canvas, which contains some custom controls of class TreeNode inherited from TextBox. The canvas control has style:

<Style x:Key="DottedStyle" TargetType="TreeBuilder:DottedCanvas">
    <!--Makes canvas dotted-->
    <Setter Property="Background" Value="{StaticResource DottedBrush}"/>
    <Style.Triggers>
        <Trigger Property="DottedEnabled" Value="False">
            <!--Removes dots when printing-->
            <Setter Property="Background" Value="White"/>
        </Trigger>
    </Style.Triggers>
</Style>

The TextBox controls are wrapped to a UserControl and also have their own style:

<Style x:Key="NodeBoxStyle" TargetType="{x:Type TreeBuilder:TreeNodeBox}">
    <Setter Property="BorderThickness" Value="1"/>
    <Style.Triggers>
        <!--Must remove d-->
        <Trigger Property="IsBeingPrinted" Value="true">
            <Setter Property="BorderThickness" Value="0"/>
        </Trigger>
    </Style.Triggers>
</Style>

Then I'm trying to print this canvas to a bitmap:

public BitmapSource BuildImage(Tree tree)
{
    canvas = tree.Canvas;
    PrepareTree(canvas);

    Size size = GetSize();
    canvas.Measure(size);
    canvas.Arrange(new Rect(size));

    RenderTargetBitmap image = new RenderTargetBitmap(
        (int)size.Width,
        (int)size.Height, 
        96, 
        96, 
        PixelFormats.Pbgra32);

    image.Render(canvas);

    UnprepareTree(canvas);

    return image;
}

private void UnprepareTree(Canvas canvas)
{
    canvas.DottedEnabled = true;

    foreach (var element in canvas.Children.OfType<IPrintable>())
    {
        element.IsBeingPrinted = false;
    }
}

private void PrepareTree(Canvas canvas)
{
    canvas.Focus();
    canvas.DottedEnabled = false;

    foreach (var element in canvas.Children.OfType<IPrintable>())
    {
        element.IsBeingPrinted = true;
    }
}

The image looks so:

Result

The Canvas has no dots (the style did its work) but the TextBox's BorderThickness stays 1 on the image. A breakpoint in PrepareTree() function shows that TextBox BorderThickness property is set to zero (that means, the style works too). How can I get the "new" version of TextBoxes on the image?

Answer 1

I succeed to solve the problem. I called Measure() and Arrange() methods on Canvas, that's why it rendered before printing. Making the same with TextBoxes helped.