How to implement binding validation for a textbox?

The following example shows the implementation of AgeRangeRule, which inherits from ValidationRule and overrides the Validate method. The Int32.Parse() method is called on the value to make sure that it does not contain any invalid characters. The Validate method returns a ValidationResult that indicates if the value is valid based on whether an exception is caught during the parsing and whether the age value is outside of the lower and upper bounds.

public class AgeRangeRule : ValidationRule
{
    private int _min;
    private int _max;

    public AgeRangeRule()
    {
    }

    public int Min
    {
        get { return _min; }
        set { _min = value; }
    }

    public int Max
    {
        get { return _max; }
        set { _max = value; }
    }

    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        int age = 0;

        try
        {
            if (((string)value).Length > 0)
                age = Int32.Parse((String)value);
        }
        catch (Exception e)
        {
            return new ValidationResult(false, "Illegal characters or " + e.Message);
        }

        if ((age < Min) || (age > Max))
        {
            return new ValidationResult(false,
              "Please enter an age in the range: " + Min + " - " + Max + ".");
        }
        else
        {
            return new ValidationResult(true, null);
        }
    }
}