WPF binding IValueConverter and the width of another control

Question

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The following code worked fine. There was an error elsewhere in the code. Still, the advice given is good.

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I am trying to bind the Width of a TextBox to a percentage of the Width of a parent control. I know I can accomplish something similar by simply setting a Margin, but I was wondering why this doesn't work.

First, I set a reference to an IValueConverter in the resources collection of my user control:

<UserControl.Resources>
    <local:TextBoxWidthConverter x:Key="txtWidthConv" />
</UserControl.Resources>

In the main xaml, I have the following:

<StackPanel Name="parentPanel" Width="300">
  <ScrollViewer HorizontalScrollBarVisibility="Auto"    
       VerticalScrollBarVisibility="Hidden" Name="scroller" Width="{Binding Width,    
       ElementName=parentPanel, Converter={StaticResource txtWidthConv}}">           
     <StackPanel Orientation="Horizontal">
       <TextBox></TextBox>
     </StackPanel>
   </ScrollViewer>
</StackPanel>

The ivalueconverter looks like this:

public class TextBoxWidthConverter : IValueConverter
{

    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        double result = (double)value;

        if (!Double.IsNaN(result))
        {
            result = result * .25;
        }
        else
        {
            result = 100D;
        }

        return result;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new System.NotImplementedException("Not implemented.");
    }

    #endregion
}

Setting the width property does nothing here, let alone setting the IValueConverter. I would expect the ScrollViewer to be 1/4 the width of the parent StackPanel.

Answer 1

Set the ScrollViewer's HorizontalAlignment to something other than Stretch.

Also, you should bind to the ActualWidth property.