Add Custom Validation Errors in Silverlight

Question

Is there any way to add custom validation errors to the list of control's errors? I know how to use IDataErrorInfo, INotifyErrorInfo, ValidationAttribute, etc, but I would like to add custom validation errors from code.

Answer 1

Found a way:

1. First, create a public class for holding our error message:

   public class TagModelError { private readonly String errorMessage;

       public TagModelError(String errorMessage)
       {
           this.errorMessage = errorMessage;
       }
   
       public Object Tag
       {
           get
           {
               return new Object();
           }
           set
           {
               throw new ValidationException(this.errorMessage);
           }
       }
   }
   

2. Next, create a helper method:

   public static void AddValidationError(this Control control, String errorMessage) { var expression = elm.GetBindingExpression(FrameworkElement.TagProperty);

       if (expression == null)
       {
           expression = control.SetBinding(FrameworkElement.TagProperty, new Binding("Tag")
           {               
               Mode = BindingMode.TwoWay,
               ValidatesOnExceptions = true,
               UpdateSourceTrigger = UpdateSourceTrigger.Explicit,
               Source = new TagModelError(errorMessage)
           }) as BindingExpression;
       }
   
       expression.UpdateSource();
   }
   

I am using the Tag property because it is seldom required, but you can use another one. The trick here is to cause an exception when writing back to the model.