Question

I have expanders that contain text boxes, the text boxes use the wpf validation stuff to draw a red box around them ( text boxes are wrapped in Adorner Decorators to make sure I don’t get empty red boxes everywhere when the expanders are collapsed)

I want to indicate in the header of the expander that it has contents that have errors (in case it is in a collapsed state) – an icon or red exclamation mark or something. I think I see a way to do this in code from my validation function (not ideal) but is there a way to do it in xaml? Can I use a style for the expander with a trigger somehow pointing to the Validation.HasError of all children?

thanks for any thoughts..

Trev

Answer 1

If you know the contents of your expander, you can use a MultiDataTrigger to do this:

<Expander>     <Expander.Header>         <TextBlock>             <TextBlock.Style>                 <Style TargetType='{x:Type TextBlock}'>                     <Setter Property='Text' Value='ERROR'/>                     <Style.Triggers>                         <MultiDataTrigger>                             <MultiDataTrigger.Conditions>                                 <Condition Binding='{Binding ElementName=txtWidth, Path=(Validation.HasError)}' Value='False'/>                                 <Condition Binding='{Binding ElementName=txtHeight, Path=(Validation.HasError)}' Value='False'/>                             </MultiDataTrigger.Conditions>                             <Setter Property='Text' Value='NO ERROR'/>                         </MultiDataTrigger>                     </Style.Triggers>                 </Style>             </TextBlock.Style>         </TextBlock>     </Expander.Header>     <StackPanel>         <TextBox x:Name='txtWidth' Text='{Binding Width, ElementName=rect, UpdateSourceTrigger=PropertyChanged, ValidatesOnExceptions=True}'/>         <TextBox x:Name='txtHeight' Text='{Binding Height, ElementName=rect, UpdateSourceTrigger=PropertyChanged, ValidatesOnExceptions=True}'/>         <Rectangle x:Name='rect' Width='100' Height='100' Margin='10' Fill='Green'/>     </StackPanel> </Expander> 

If the contents of the expander aren’t known, then you’ll probably have to set Binding.NotifyOnValidationError on the TextBoxes and handle the Error attached event.