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Show Error Message in Textbox

See original GitHub issue

I have a Textbox that I just want user’s input is numeric, I use Validation Rule then I custom ErrorTemplate but I can’t show any message in Template. This is my Textbox: <TextBox Margin="100,20,100,0" x:Name="txbSDT" FontSize="14" FontFamily="/CoffeeHome;component/CoffeeHomeFont/#Roboto" materialDesign:HintAssist.Hint="Số điện thoại" Style="{StaticResource MaterialDesignFloatingHintTextBox}" Validation.ErrorTemplate="{StaticResource textBoxErrorTemplate}"> <TextBox.Text> <Binding Path="Staff.Sdt" UpdateSourceTrigger="PropertyChanged"> <Binding.ValidationRules> <validation:NumericValidation PropertyName="Số điện thoại" ValidatesOnTargetUpdated="True"/> </Binding.ValidationRules> </Binding> </TextBox.Text> </TextBox>

And this is my ErrorTemplate: <ControlTemplate x:Key="textBoxErrorTemplate"> <StackPanel> <Border BorderBrush="Red" BorderThickness="1"> <AdornedElementPlaceholder Name="a" /> </Border> <TextBlock Foreground="Red" Text="{Binding [0].ErrorContent}"/> </StackPanel> </ControlTemplate>

In the preview of Visual Studio I can still see the message but when I build and test the message doesn’t show. I can’t understand, is it because of the default of Material Design ? If someone can help me out, I will very grateful