Bind DataGrid Column Width to Two Colums of Another DataGrid

Question

Question: How do I bind StatName.Width to Samp1.ActualWidth + Samp2.ActualWidth?

Sub-questions:<

Answer 1

The code finally executes as expected with the following:

• <Binding Source="{x:Reference Samp2}" Path="ActualWidth" />
• return new DataGridLength(totalWidth);

The Converter gets called on load and when resizing Samp1 or Samp2. The column widths remain synchronized as expected.

<DataGridTextColumn x:Name="StatName"  Binding="{Binding a}" Header="Stat">
   <DataGridTextColumn.Width >
       <MultiBinding Converter="{StaticResource WidthConverter}">
           <Binding Source="{x:Reference Samp1}" Path="ActualWidth" />
           <Binding Source="{x:Reference Samp2}" Path="ActualWidth" />
       </MultiBinding>
   </DataGridTextColumn.Width>
</DataGridTextColumn>

The Convert function needed to return a DataGridLength, the data type of DataGridTextColumn.Width.

public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{

    double totalWidth = 0;

    foreach (double Width in values)
        totalWidth += Width;

    return new DataGridLength(totalWidth);
}

Note: The code executes as expected, regardless of the error Specified cast is not valid.

1. The Visual Studio designer underlines the entire tag <MultiBinding ... </MultiBinding> in cyan.
2. The Error List window reports the error "Specified cast is not valid."
3. While it is displayed as an error, Visual Studio will still build and execute the code.