Question

I am trying to use Validation in WPF. I created a NotNullOrEmptyValidationRule as shown below:

public class NotNullOrEmptyValidationRule : ValidationRule     {         public override ValidationResult Validate(object value, CultureInfo cultureInfo)         {             if (String.IsNullOrEmpty(value as String))                 return new ValidationResult(false, 'Value cannot be null or empty');              return new ValidationResult(true, null);          }     } 

Now, I need to use it in my application. In my App.xaml file I declared the Style for the TextBox. Here is the declaration.

 <Style x:Key='textBoxStyle' TargetType='{x:Type TextBox}'>              <Setter Property='Background' Value='Green'/>              <Style.Triggers>                  <Trigger Property='Validation.HasError' Value='True'>                      <Setter Property='Background' Value='Red'/>                     <Setter Property='ToolTip' Value='{Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent}'/>                  </Trigger>              </Style.Triggers>          </Style> 

Now, I want to use it on my TextBox so I am using the following code:

  <TextBox Style='{StaticResource textBoxStyle}'>                 <TextBox.Text>                     <Binding>                         <Binding.ValidationRules>                             <NotNullOrEmptyValidationRule />                         </Binding.ValidationRules>                     </Binding>                 </TextBox.Text>               </TextBox> 

The error comes on the Tag NotNullOrEmptyValidationRule. The XAML syntax checker is not able to resolve the NotNullOrEmptyValidationRule. I have even tried putting the namespace but it does not seem to work.

Answer 1

i see your binding on the TextBox is set to a path of ‘Text’ – is that a field on whatever the datacontext of this textbox is? is the textbox actually getting a value put into it? also, if you put a breakpoint in your validation method, is that ever getting fired?

you may want to lookup how to log failures in binding and review those as well..