How to add a binding to a property on a ValidationRule

You can't add bindings to properties on classes that derive from ValidationRule in the normal way. This is because validation rules don't sit in an inheritance context and don't derive from DependencyObject.

Fortunately, this can easily be worked around using the DataResource technique from a previous post. Here's how you would use this technique for max/min integer validation.

First create the rule class:

public class IntValidationRule : ValidationRule
{
    public int Max { get; set; }
    public int Min { get; set; }

    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        try
        {
            int i = Convert.ToInt32(value);
            return (i < Min || i > Max) ?
                new ValidationResult(false, "int out of range") :
                new ValidationResult(true, null);
        }
        catch (FormatException fe)
        {
            return new ValidationResult(false, fe.Message);
        }
    }
}

...the DataResources and the associated bindings should then simply be set up like this:

<Window.Resources>
    <my:DataResource x:Key="max" BindingTarget="{Binding Max}"/>
    <my:DataResource x:Key="min" BindingTarget="{Binding Min}"/>
</Window.Resources>

<TextBox>
    <TextBox.Text>
        <Binding UpdateSourceTrigger="PropertyChanged" Path="Value">
            <Binding.ValidationRules>
                <my:IntValidationRule 
                    ValidatesOnTargetUpdated="True" 
                    Min="{my:DataResourceBinding DataResource={StaticResource min}}"
                    Max="{my:DataResourceBinding DataResource={StaticResource max}}">
                </my:IntValidationRule>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

DataResource.cs
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