How To Validation This Class?(WPF)

Question

I can not understand is the Property Value for each.

For this method : public override ValidationResult Validate(object value.

name maximum char must be 10; age maximum value must be 150;

public class Person : ValidationRule
    {
        string _Name;

        public string Name
        {
            get
            {
                return _Name;
            }
            set
            {
                _Name = value;
            }
        }

        int _age = 20;

        public int Age
        {
            get { return _age; }
            set { _age = value; }
        }

        string _Phone = "000-0000";

        public string Phone
        {
            get { return _Phone; }
            set { _Phone = value; }
        }

        public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
        {
            **//is value Which Property?**
              //I can not understand is the Property Value for each
            return new ValidationResult(true, null);
        }
    }

Robert Rossney · Accepted Answer · 2011-10-05 17:40:51Z

You can't make your class derive from ValidationRule: it's a person, not a rule.

First, I don't recommend that WPF developers use validation rules at all. Use MVVM, and have your view model implement IDataErrorInfo as described (for instance) here.

If you want to create a single ValidationRule class to validate your Person class, you can, but you'll need to create a PropertyName property on the class and set it in your XAML, e.g.:

<TextBox>
  <TextBox.Text>
    <Binding Path="Age"
             Mode="TwoWay">
      <Binding.ValidationRules>
        <local:PersonValidationRule PropertyName="Age"/>
      </Binding.ValidationRules>
    </Binding>
  </TextBox.Text>
</TextBox>

Then the Validate method in this class can look at the PropertyName and branch accordingly. Of course, now you've implemented a new point of failure - what happens if you put down the wrong property name in your XAML? If you use data-error validation, that can't happen.

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