What is the best way to handle validation in WPF?

Question

i would like to implement the validation mechanism which simulates Errorprovider in winforms. i tried to use IDataErrorInfo but the problem is it is trying to perform validation on the form load. my requirement is i need to perform validation on click of a button in the page. Is there any other better approach to perform validation in WPF?

Answer 1

Sounds like you have validation figured out now it the easy part - prevent it from validating until needed.. Put a bool property on the class that implements IErrorInfo:

public bool IsReadyToValidate {get;set;}

in each property

public object SomeProperty
{
  get {return _someProperty;}
  set
      {
         if(_someProperty == value) return;
         _property = value;
         if(IsReadyToValidate) 
               //do validation

or if you use attribute based validation:

[CustomMethodValidator("ValidateSomeProperty")]
    public string SomeProperty
    {
        if(_someProperty == value) return;
        set
        {
             if(_property == value)
                                return;
                            _property = value;
            RaisePropertyChanged(() => SomeProperty);
        }
    }

  private bool ValidateSomeProperty()
  {
       bool isValid = true;
       if(IsReadyToValidate)
          //do validation

        return is valid;

On the click of your button, set the IsReadyToValidate to true and revalidate. Again it all depends on your implementations. Put maybe a method like this?

public void Validate()
    {
        foreach (var prop in PropertiesWithValidators[GetType()])
            ValidateProperty(prop.Name);

        HasErrors = _errorDictionary.Count > 0;
        RaisePropertyChanged(() => Error);
    }

or you could do some brute way, like restuffing the properties after you flipped the flag to validate

 public void Validate()
 {
     IsReadyToValidate = true;
     //now it will validate:
     SomeProperty = SomeProperty;