How to force TimeSpan to be depended with enabled/disabled button WPF

Question

I have a TimeSpan textbox, my objectif is to disable the button Save when the form of TIMESPAN is wrong (exp 90:00:00)..

I try a code, it is correct for just once time..if I set 20:10:00 ..The Save button is enabled (correct). After that however the TIMESPAN is wrong 55:00:00, the button is enabled ( and the saving in database is 00:00:00)

The XAML :

 <TextBox Name="txtTime"  Margin="10,10,10,10" >
                <TextBox.Text >
                    <Binding Path="Time" UpdateSourceTrigger="PropertyChanged" NotifyOnValidationError="True" Mode="TwoWay" >
                        <Binding.ValidationRules>
                            <local:DateTimeValidationRule ValidationStep="RawProposedValue"/>
                        </Binding.ValidationRules>
                    </Binding>
                </TextBox.Text>
            </TextBox>

The ViewModel :

public bool  VarTIME ;



  [Required(ErrorMessage = "Time is required")]
    public TimeSpan Time
    {
        get { return time; }
        set
        {
            time = value;
            intervalString = Time.ToString();
            TimeSpan reded;
            bool success = TimeSpan.TryParseExact(intervalString, "hh\\:mm\\:ss",
                           CultureInfo.InvariantCulture, out reded);

            if (success)
            {
                VarTIME = true;
            }
            OnPropertyChanged("Time");
        }
    }


    public SheduleTrainViewModel()
    {
        VarTIME = false;
        addTrain = new RelayCommand<string>(AddTrainFunction, canAddTrain);

        private bool canAddTrain(string obj)
         {     return VarTIME;     

         }
    }

The VelidationResult class:

 public class DateTimeValidationRule: ValidationRule
{
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        string time;
        Regex regex;
        if (value == null)
            return new ValidationResult(true, null);
        else
            time = value.ToString();

        regex = new Regex(@"^([0-1]?\d|2[0-3])(?::([0-5]?\d))?(?::([0-5]?\d))?$");
        if (regex.IsMatch(time.ToString()))
            return new ValidationResult(true, null);

        return new ValidationResult(false, "The time must match this format hh:mm:ss / hh:mm");
    }
}

How I can fix it to be work always correct? Thanks,

Answer 1

You can't set a TimeSpan property to anything else than a valid TimeSpan value so doing the validation in the setter of the source property is meaningless.

value is always a valid TimeSpan.

You should perform the validation in the ValidationRule :

public class DateTimeValidationRule : ValidationRule
{
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        TimeSpan reded;
        if(!TimeSpan.TryParseExact(value.ToString(), "hh\\:mm\\:ss", CultureInfo.InvariantCulture, out reded))
            return new ValidationResult(false, "Invalid time!");

        return ValidationResult.ValidResult;
    }
}

It this validation fails, the TextBox will get a red border (using the default Validation.ErrorTemplate) that indicates that the value cannot be converted to a TimeSpan and the property won't be set.