Hi Tacho,

Thank you so much for your reply.  I almost got it to work.  Here are few changes that I made. 

1. I should not display the error icon.  So I set the DataErrorDisplayMode ="highlight" only in the xamdatagrid.

2. I added triggers to the tooltip template to show tooltip only if Host.HasDataError = True

3. I added Tooltip property to the DataErrorContentTemplateKey's DataTemplate

It's working fine except half the time I get a blank tooltip when I hover the mouse on an invalid cell if:

1. I first select a cell with no error in the same column (put it in edit mode)

2. Then I move the mouse to an invalid cell either above or below the selected cell within the same column

Do you know why half the time the tooltip is blank?

 Below is the modified xaml to display tooltip only if there is error.

<!-- ============ Tooltip with template ============ -->
<ToolTip Name="errorTooltip" x:Key="tooltip" Placement="Right" Margin="10,0,0,0">
   <ToolTip.Template>
      <ControlTemplate>
         <Border Background="#fc5236" BorderBrush="DarkRed" BorderThickness="1">
            <TextBlock Text="{Binding Host.DataError}" Foreground="White" Margin="4,2,4,2" />
         </Border>
         <ControlTemplate.Triggers>
         <MultiDataTrigger>
            <MultiDataTrigger.Conditions>
               <Condition Binding="{Binding Host.HasDataError}" Value="True" />
            </MultiDataTrigger.Conditions>
               <Setter Property="Visibility" Value="Visible" />
         </MultiDataTrigger>
         <MultiDataTrigger>
            <MultiDataTrigger.Conditions>
               <Condition Binding="{Binding Host.HasDataError}" Value="False" />
            </MultiDataTrigger.Conditions>
               <Setter Property="Visibility" Value="Collapsed" />
         </MultiDataTrigger>
         </ControlTemplate.Triggers>
      </ControlTemplate>
   </ToolTip.Template>
</ToolTip>

<!--============ Style for error content ============-->
<DataTemplate x:Key="{x:Static igDP:DataPresenterBase.DataErrorContentTemplateKey}" >
   <Grid ToolTip ="{StaticResource tooltip}">
      <Grid.ColumnDefinitions>
         <ColumnDefinition Width="*" />
         <ColumnDefinition Width="Auto" />
      </Grid.ColumnDefinitions>
      <!-- ============= Content presenter to display the cell's value ============= -->
   <Grid Background="DarkRed" >

      <ContentPresenter ContentTemplate="{x:Null}" />
   </Grid>
   <!-- ============= Control for the error icon ============= -->
      <Control Grid.Column="1"
         Name="errorIcon"
         Visibility="Collapsed"
         Style="{DynamicResource {x:Static igDP:DataPresenterBase.DataErrorIconStyleKey}}"
         ToolTip="{StaticResource tooltip}">
      </Control>
      <!--============= Border for the highlight ============= -->
      <Border Name="errorHighlight" BorderBrush="Blue" BorderThickness="0.7" />
   </Grid>

Hello Marlon,

Thank you for the feedback and code-snippet you have provided.

Setting data triggers for both when the HasDataError property is True and False can interfere with the neighbouring cells from the field.
An approach I can suggest you in order to avoid the empty ToolTip is to set its Visibility to Hidden when the HasDataError is False.

<MultiDataTrigger>
    <MultiDataTrigger.Conditions>
        <Condition Binding="{Binding Host.HasDataError}" Value="False" />
    </MultiDataTrigger.Conditions>
<Setter Property="Visibility" Value="Hidden" />
</MultiDataTrigger>

I have attached a sample application that demonstrates the approach from above.

If you have any questions, please let me know.

Hi Tacho,

Thank you for a quick reply.  Yes that fixed the blank tooltip problem.

Another requirement that I have which I am not sure how to implement is when an invalid cell is selected and in edit mode, we also ant to have the dark red background and light red border.  Can you show how to implement that?

Thank you.

Hello Marlon,

When the CellValuePresenter is in edit mode, we are actually working with its respective editor (for example: XamNumericEditor, XamTextEditor, etc.).
This why in order to change the filling color of our cell in edit mode, we will have to set the Background of the corresponding editor.

For example:

<Style TargetType="igEditors:XamTextEditor">
    <Style.Triggers>
        <MultiDataTrigger>
            <MultiDataTrigger.Conditions>
                <Condition Binding="{Binding Path=IsInEditMode, RelativeSource={RelativeSource AncestorType=igDP:CellValuePresenter}}" Value="True" />
                <Condition Binding="{Binding Path=HasDataError, RelativeSource={RelativeSource AncestorType=igDP:CellValuePresenter}}" Value="True" />
                <Condition Binding="{Binding Path=IsDataErrorDisplayModeHighlight, RelativeSource={RelativeSource AncestorType=igDP:CellValuePresenter}}" Value="True" />
            </MultiDataTrigger.Conditions>
            <Setter Property="Background" Value="DarkRed" />
        </MultiDataTrigger>
    </Style.Triggers>
</Style>

<Style TargetType="igEditors:XamCurrencyEditor">
    ...
</Style>
<Style TargetType="igEditors:XamNumericEditor">
    ...
</Style>

Please note that since the fields could use different editors depending on the data they are containing, we will have to include a Style for all the editors that are used by the fields.
I have attached a sample application that demonstrates the approach from above.

If you have any questions, please let me know.