Display DataGrid-ValidtionError in ToolTip

Question

I am using a DataGrid for showing and editing data. The view (datagrid) is bound to a viewmodel. No I added a custom ValidationRule (following this tutorial: http://blogs.u2u.be/diederik/post/2009/09/30/Validation-in-a-WPF-DataGrid.aspx)

namespace Presentation.ViewsRoot.ValidationRules
{
    class IsPositiveIntegerRule : ValidationRule
    {
        public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
        {
            if (string.IsNullOrEmpty(value as string))
            {
                return new ValidationResult(true, null);
            }
            else
            {
                int proposedValue;

                if (!int.TryParse(value.ToString(), out proposedValue))
                {
                    return new ValidationResult(false, "'" + value.ToString() + "' ist no positive integer (>=0).");
                }

                if (proposedValue < 0)
                {
                    // Something was wrong.
                    return new ValidationResult(false, "Value can't be smaller than 0.");
                }
            }

            // Everything OK.
            return new ValidationResult(true, null);
        }
    }
}

I am binding to this validationrule in xaml

<DataGridTextColumn Header="Shitfs" IsReadOnly="False">
   <DataGridTextColumn.Binding>
       <Binding Path="Shifts">
          <Binding.ValidationRules>
             <validationRules:IsPositiveIntegerRule />
          </Binding.ValidationRules>
       </Binding>
   </DataGridTextColumn.Binding>
</DataGridTextColumn>

The cell gets a red border when entering wrong values and the rowheader shows a red exclamation mark (!). But no Tooltip with message is shown. I tried adding a custom style in UserControl.Resources but it didn't work:

<Style TargetType="TextBlock">
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
            <Setter Property="ToolTip"
               Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                  Path=(Validation.Errors)[0].ErrorContent}"/>
        </Trigger>
    </Style.Triggers>
</Style>

Any ideas on how to show the errorcontent in a tooltip in a datagrid? I think I am missing something essential, but I can't find what...

Working Solution:

<Style x:Key="CellEditStyle" TargetType="TextBox">
   <Style.Triggers>
       <Trigger Property="Validation.HasError" Value="true">
           <Setter Property="ToolTip"
                   Value="{Binding RelativeSource={RelativeSource Self},
                   Path=(Validation.Errors)[0].ErrorContent}"/>
       </Trigger>
   </Style.Triggers>
</Style>

Combining the comments about using {Binding RelativeSource Self} and referencing it by name works. I also had to change TargetType from TextBlock to TextBox. Thanks for the helpful comments.

In my case it did work with RelativeSource={RelativeSource Self} — Florian Gl
@FlorianGl : Changed to <Setter Property="ToolTip" Value="RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> -> no tooltip :( — basti
Try <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> — Florian Gl
@FlorianGl if you post your comment as an answer I will accept it. So its at least aviable on google etc. :) — basti

Florian Gl Florian Gl · Accepted Answer · 2012-09-27T13:27:13

Try

<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/>

Display DataGrid-ValidtionError in ToolTip

1 Answers