WPF ValidationRule Binding is throwing XMLParseException

I have the following ValidationRule class in WPF

public class EmptyFieldValidationRule: BaseValidationRule
{
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        var fieldValue = (string)value;
        if (fieldValue.Trim().Length == 0)
        {
            return new ValidationResult(false, "Field Is Empty");
        }
        else
       开发者_运维百科 {
            return new ValidationResult(true, null);
        }
    }
}

NOTE - BaseValidationRule extends the normal ValidationRule class.

This is really just a test validation class because I wanted to start off easier.

I am attempting to bind this to a textbox in my XAML, and it is reading in the BaseValidationRule class fine, it is even giving me it in Intellisense, but when I go to run the program and it hits that part of the application, it tells me an XMLParseException.

I am defining an ErrorMessage property in the XAML, which is inherited in the EmptyFieldValidationRule class from the BaseValidationRule.

The XAML for the ValidationRule Binding looks like the following

The Error Message I am getting is the following.

XAMLParseException occured, Could not load file or assembly XXX.ValidationRule, Public KeyToken = null, or one of its dependencies. The system cannot find the file specified.

I have made the reference available to the ValidationRule assembly, and the intellisense is reading in the ValidationRule fine in my XAML, is there something else I need to do?

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Please, make sure you have a XML namespace defined in your XAML document as follows:

xmlns:validation="clr-namespace:Some.Assembly.Name.Some.Namespace.Containing.Validations;assembly=Some.Assembly.Name"

Where Some.Assembly.Name.Some.Namespace.Containing.Validations should be your namespace full name containg EmptyFieldValidationRule class, and Some.Assembly.Name should be library name for that class.

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Is the reference to the validation assembly in the project with the XAML set to "Copy Local = True" ? If not, this would explain the issue.