WPF DataBinding and Validation - wpf

Question

I have a WPF User Interface and I've implemented bound ValidationRules with UpdateSourceTrigger="Explicit". I'm finding that it works perfectly when I have the tab page where the fields being validated is visible:
but if I'm on the third tab page where the form ends and trigger the UpdateSources method on the BindingExpressions for the fields being Validated then when I step back to the first tab the fields aren't actually highlighted in red. Even once I'm back on that tab page and re-trigger they don't highlight even though they're empty. I need to enter a value, re-trigger, then delete the value and re-trigger, THEN the modified ones get highlighted.
Anyone know how to address this behaviour?
Also is there a way to force a specific tab page to be switched to when the Validation fails, switching to the page which has the first field to fail?
I know there's an option to go with PropertyChanged and LostFocus but I'd like to get full form entry first and do all validation in one hit at the end.

Answer 1

It's because of the way the TabControl handles the AdornerLayer. They are obviously not preserved when the TabItem is switched. It works when you force to re-render the AdornerLayer when switching back to the TabItem.
<!-- Custom error template -->
<ControlTemplate x:Key="ValidationErrorTemplate">
<StackPanel>
<!-- Placeholder for the TextBox itself -->
<AdornedElementPlaceholder />
<TextBlock Text="{Binding ErrorContent}"
Foreground="Red" />
</StackPanel>
</ControlTemplate>
<!-- Style to trigger the rendering of the AdornerLayer by setting the error template -->
<Style TargetType="TextBox">
<Setter Property="Validation.ErrorTemplate"
Value="{x:Null}" />
<Style.Triggers>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="Validation.HasError"
Value="True" />
<Condition Property="IsVisible"
Value="True" />
</MultiTrigger.Conditions>
<Setter Property="Validation.ErrorTemplate"
Value="{StaticResource ValidationErrorTemplate}" />
</MultiTrigger>
</Style.Triggers>
</Style>
Consider to disallow leaving the current tab if it has validation errors to avoid this behavior.