Question

I have a user control which contains a textbox. I have a class called Person which implements IDataErrorInfo interface:

class Person : IDataErrorInfo { private bool hasErrors = false; #region IDataErrorInfo Members          public string Error         {                         get              {                 string error = null;                 if (hasErrors)                 {                     error = 'xxThe form contains one or more validation errors';                 }                 return error;             }         }          public string this[string columnName]         {             get              {                 return DoValidation(columnName);             }         }         #endregion } 

Now the usercontrol exposes a method called SetSource through which the code sets the binding:

public partial class TxtUserControl : UserControl      {                   private Binding _binding;          public void SetSource(string path,Object source)         {             _binding = new Binding(path);             _binding.Source = source;             ValidationRule rule;             rule = new DataErrorValidationRule();             rule.ValidatesOnTargetUpdated = true;                         _binding.ValidationRules.Add(rule);             _binding.ValidatesOnDataErrors = true;             _binding.UpdateSourceTrigger = UpdateSourceTrigger.LostFocus;             _binding.NotifyOnValidationError = true;                         _binding.ValidatesOnExceptions = true;             txtNumeric.SetBinding(TextBox.TextProperty, _binding);                         } ... } 

The WPF window that includes the user control has the following code:

public SampleWindow()     {         person= new Person();         person.Age = new Age();         person.Age.Value = 28;          numericAdmins.SetSource('Age.Value', person);     }     private void btnOk_Click(object sender, RoutedEventArgs e)     {                   if(!String.IsNullOrEmpty(person.Error))         {             MessageBox.Show('Error: '+person.Error);         }     } 

Given this code, the binding is working fine, but the validation never gets triggered. Whats wrong with this code?

Answer 1

Your Age class will need to implement IDataErrorInfo. Your Person class won’t be asked to validate the Age‘s properties.

If that is not an option, I wrote a validation system for WPF that is extensible enough to support this. The URL is here:

• http://paulstovell.com/Downloads/ValidationScopes.zip

In the ZIP is a word document describing it.

Edit: here’s one way age could implement IDataErrorInfo without being too smart:

class Constraint  {     public string Message { get; set; }     public Func<bool> Validate;     public string Name { get; set; } }  class Age : IDataErrorInfo {     private readonly List<Constraint> _constraints = new List<Constraint>();      public string this[string columnName]     {         get          {             var constraint = _constrains.Where(c => c.Name == columnName).FirstOrDefault();             if (constraint != null)             {                 if (!constraint.Validate())                 {                     return constraint.Message;                 }             }             return string.Empty;         }     } }  class Person {     private Age _age;      public Person()      {         _age = new Age(             new Constraint('Value', 'Value must be greater than 28', () => Age > 28);     } } 

Also see this link:

http://www.codeproject.com/KB/cs/DelegateBusinessObjects.aspx