Hi !

I have a control with this validation

<MyPicker.SelectedItem>
    <Binding Path="Person.Value" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnValidationError="True">
        <Binding.ValidationRules>
            <rules:MyValidationRule ValidationType="notnull"/>
        </Binding.ValidationRules>
    </Binding>
</MyPicker.SelectedItem>

This is the Validation Class:

class MyValidationRule : ValidationRule
{        
    private string _validationType;
    public string ValidationType
    {
        get { return _validationType; }
        set { _validationType = value;  }
    }

    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {            
        ValidationResult trueResult = new ValidationResult(true, null);

        switch (_validationType.ToLower())
        {
            case "notnull": return value == null ? new ValidationResult(false, "EMPTY FIELD") : trueResult;               
            default: return trueResult;
        }
    }
}

Question: When the property is changed, then the Validate( ) method is called which is correct.

But to call this method at the very beginning when the MyControl is created? I need to prove immediate after initialize if the there's a null value in the control (and display a validation error)