Attached Properties in DataGrid

Question

I am using an attached property to limit the input into textboxes and textblocks to either numeric or alphabetic. Now I would like to apply this attached property to a datagridtextcolumn. I tried the following:

<DataGridTextColumn Header="Max" Width="50"
                                  Binding="{Binding Path=Max, Mode=TwoWay"
                                  Helper:InputService.NumericOnly="True">

and something like this:

 <DataGridTextColumn.ElementStyle>
                      <Style>
                        <Setter Property="Helper:InputService.NumericOnly" Value="True"/>
                      </Style>
                </DataGridTextColumn.ElementStyle>

But it does not work. How do I do it right?

My InputService contains the NumericOnly property:

 public static readonly DependencyProperty NumericOnlyProperty =          DependencyProperty.RegisterAttached(
     "NumericOnly",
     typeof(bool),
     typeof(InputService),
     new UIPropertyMetadata(false, OnNumericOnlyChanged));


public static bool GetNumericOnly(DependencyObject d)
{
  return (bool)d.GetValue(NumericOnlyProperty);
}


public static void SetNumericOnly(DependencyObject d, bool value)
{
  d.SetValue(NumericOnlyProperty, value);
}

private static void OnNumericOnlyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
  bool isNumericOnly = (bool)e.NewValue;

  if (d is TextBox)
  {
    var textBox = (TextBox)d;

    if (isNumericOnly)
    {
      textBox.PreviewTextInput += BlockNonDigitCharacters;
      textBox.PreviewKeyDown += ReviewKeyDown;
    }
    else
    {
      textBox.PreviewTextInput -= BlockNonDigitCharacters;
      textBox.PreviewKeyDown -= ReviewKeyDown;
    }
  }
  else if (d is TextBlock)
  {
    var textBlock = (TextBlock)d;

    if (isNumericOnly)
    {
      textBlock.PreviewTextInput += BlockNonDigitCharacters;
      textBlock.PreviewKeyDown += ReviewKeyDown;
    }
    else
    {
      textBlock.PreviewTextInput -= BlockNonDigitCharacters;
      textBlock.PreviewKeyDown -= ReviewKeyDown;
    }
  }
}


private static void BlockNonDigitCharacters(object sender, TextCompositionEventArgs e)
{
  foreach (char ch in e.Text)
  {
    if (Char.IsDigit(ch))
    {
      e.Handled = true;
    }
  }
}

Answer 1

Ok, this it what works for me:

         <DataGridTextColumn.EditingElementStyle>
            <Style TargetType="TextBox">
              <Setter Property="Helper:InputService.NumericOnly" Value="True"/>
            </Style>
          </DataGridTextColumn.EditingElementStyle>

Answer 2

Your property implementation expects only to be set on a TextBox or TextBlock. I would suggest that you put a breakpoint in your code and check what type of control it's actually being set on - I suspect you'll find it's the parent container of your cell, rather than the text control itself.

EDIT: based on your comment, you probably want to include the following in your binding:

Binding="{Binding Path=Max, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

This will cause the binding to refresh every time the property changes, where the default for most input controls is to fire when a control loses focus.