Question

I have a cell template for listview is defined as follows:

<DataTemplate x:Key="editableIPAddressColTemplate">
    <Grid x:Name="dtTemplateGrid">
        <TextBlock Width="100" FontSize="11" Text="{Binding ElementName=txt, Path=Text, Mode=TwoWay}" 
                   ToolTip="{Binding ElementName=txt, Path=ToolTip, Mode=OneWay}"
                        Style="{StaticResource GridBlockStyle}">
        </TextBlock>
        <TextBox x:Name="txt" FontSize="11" Width="100" Style="{StaticResource GridEditStyle}"
                 Validation.Error="TextBox_Error" LostFocus="txt_LostFocus" >
            <Binding Path="IPAddress" Mode="TwoWay" ValidatesOnDataErrors="True" 
                     ValidatesOnExceptions="True" NotifyOnValidationError="True">
                <Binding.ValidationRules>
                    <local:IPAddressValidationRule>
                        <local:IPAddressValidationRule.Params>
                            <local:ValidationParameters BoundListView="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type ListView}}}"/>
                        </local:IPAddressValidationRule.Params>
                    </local:IPAddressValidationRule>
                </Binding.ValidationRules> 
            </Binding>
        </TextBox>
    </Grid>                
</DataTemplate>

The IPAddressValidationRule is derived from ValidationRule and has a property called Params which is of type ValidationParameters. The ValidationParameters class is derived from dependency object and has a property called BoundListView which is of type ListView.

When I see through debugger, in side the IPValidationRule class, the BoundListView property is always null. What am I doing wrong?

I would greatly appreciate if anybody can help me figure out this.

Thanks a lot in advance.

Answer 1

You have a break in the tree, the validation rules just float about as property of a binding, you cannot use ElementName or RelativeSource in such a disconnected place. Check the output window and you should be able to see some binding errors regarding this.

You could try naming the ListView and set the Binding.Source using x:Reference (x:Reference does not like cyclical dependencies, so you need to watch out for that)