Binding DataContext to ValidationRule

Question

I have a custom ValidationRule that requires access to the ViewModel in order to validate a supplied value in conjunction with other properties of the ViewModel. I previously tr

Answer 1

After some research, I have come up with the following code which works exactly as the DataErrorValidationRule works.

class VJValidationRule : System.Windows.Controls.ValidationRule
{
    public VJValidationRule()
    {
        //we need this so that BindingExpression is sent to Validate method
        base.ValidationStep = System.Windows.Controls.ValidationStep.UpdatedValue;
    }

    public override System.Windows.Controls.ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        System.Windows.Controls.ValidationResult result = System.Windows.Controls.ValidationResult.ValidResult;

        System.Windows.Data.BindingExpression bindingExpression = value as System.Windows.Data.BindingExpression;

        System.ComponentModel.IDataErrorInfo source = bindingExpression.DataItem as System.ComponentModel.IDataErrorInfo;

        if (source != null)
        {
            string msg = source[bindingExpression.ParentBinding.Path.Path];

            result = new System.Windows.Controls.ValidationResult(msg == null, msg); 
        }

        return result;
    }