How do I pass ValidationRules an Interface List to validate against?

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C#

XAML

WPF

validation

I have a textbox and I am trying to use validation rules to verify that the text entered is has not already been used before. To do so I want to send the Validation rule a list of the existing strings.

<TextBox Name="txtModuleName" Grid.Column="1" Margin="5">
    <TextBox.Text>
        <Binding FallbackValue="59" RelativeSource="{RelativeSource Self}" Path="Text">
            <Binding.ValidationRules>
                <val:StringRangeValidationRule
                    MinimumLength="1"
                    ErrorMessage="Module Name is required."/>
                <val:StringNotInListValidationRule
                    ErrorMessage="Module Name already Exists."
                    ListToCompare="{DynamicResource list}"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

This is my rather simple Validation rule I am trying to use.

public class StringNotInListValidationRule : ValidationRule
   {
       public List<ISearch> ListToCompare { get; set; }

       public string ErrorMessage { get; set; }

       public override ValidationResult Validate(object value, CultureInfo cultureInfo)
       {
           ValidationResult result = new ValidationResult(true, null);
           string inputString = (value ?? string.Empty).ToString();
           if (null == ListToCompare || ListToCompare.Exists(x => x.Name == inputString))
           {
               result = new ValidationResult(false, this.ErrorMessage);
           }

           return result;
       }
   }

   public interface ISearch
   {
       string Name { get; set; }
   }

I know DynamicResource doesn't work for the 'ListToCompare'. That is what I am trying to figure out. How can I send the list to the validation rule? Do I need to change the Interface?

Any suggestions would be appreciated.