Binding to a ValidationRule in WPF

Question

I am new to WPF. The form's data context includes a StartTime and an EndTime field (using MVVM), which I have successfully bound to their own text boxes. I am trying to create a validation to check that a new user-entered StartTime is before the EndTime value. The following code does not seem to bind the EndTime field to the validation parameter Maximum.

XAML:

<TextBox>
    <TextBox.Text>
        <Binding Path="StartTime" UpdateSourceTrigger="LostFocus" StringFormat="{}{0:hh}:{0:mm}">
            <Binding.ValidationRules>                                            
                <local:ValidateTime>
                    <local:ValidateTime.Maximum>
                        <local:ValidationParameter Parameter="{Binding EndTime, StringFormat=hh\\:mm}" />
                    </local:ValidateTime.Maximum>
                </local:ValidateTime>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

View model:

public class ValidationParameter : DependencyObject
{
    public static readonly DependencyProperty ParameterProperty = DependencyProperty.Register(
        "Parameter",
        typeof(string),
        typeof(ValidationParameter),
        new FrameworkPropertyMetadata(null));

    public string Parameter
    {
        get { return (string)GetValue(ParameterProperty); }
        set { SetValue(ParameterProperty, value); }
    }
}

public class ValidateTime : ValidationRule
{
    private TimeSpan _Minimum = new TimeSpan(0, 0, 0);
    private TimeSpan _Maximum = new TimeSpan(23, 59, 9);
    private ValidationParameter _MinimumProperty;
    private ValidationParameter _MaximumProperty;

    public ValidationParameter Minimum
    {
        get
        {
            return _MinimumProperty;
        }
        set
        {
            TimeSpan ts;
            if (TimeSpan.TryParse(value.Parameter, out ts))
            {
                _Minimum = ts;
                _MinimumProperty = value;
            }
        }
    }

    public ValidationParameter Maximum
    {
        get 
        {
            return _MaximumProperty;
        }
        set 
        {
            TimeSpan ts;
            if (TimeSpan.TryParse(value.Parameter, out ts))
            {
                _Maximum = ts;
                _MaximumProperty = value;
            }
        }
    }

    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        string formattedValue = value.ToString();
        if (Regex.IsMatch(formattedValue, @"^\d{4}$"))
        {
            formattedValue = string.Format("{0}:{1}", formattedValue.Substring(0, 2), formattedValue.Substring(2, 2));
        }
        TimeSpan convertedValue;
        if (TimeSpan.TryParseExact(formattedValue, "g", System.Globalization.CultureInfo.CurrentCulture, out convertedValue))
        {
            if (convertedValue > _Maximum)
            {
                return new ValidationResult(false, string.Format("Time must be before {0}.", _Maximum.ToString("g")));
            }
            else if (convertedValue < _Minimum)
            {
                return new ValidationResult(false, string.Format("Time must be after {0}.", _Minimum.ToString("g")));
            }
            return ValidationResult.ValidResult;
        }
        else
        {
            return new ValidationResult(false, string.Format("'{0}' is not a valid time entry.", value.ToString()));
        }
    }
}

The code works if I set the parameter to a static value like the following, but I need this validation to be dynamic:

<local:ValidateTime.Maximum>
    <local:ValidationParameter Parameter="12:00" />
</local:ValidateTime.Maximum>

duplicate of http://stackoverflow.com/questions/36083103/binding-inputvalidation-additional-data-using-dependencyproperty/36087560#36087560 — J.H., Mar 23 '16 at 20:33

score 0 · Answer 1 · answered Mar 23 '16 at 19:30

First you want to give your TextBox a name like so:

<TextBox Name="StartTime"/>

Then you set the parameter for validation like so:

<local:ValidateTime.Maximum>
    <local:ValidationParameter Parameter="{Binding ElementName=StartTime, Path=Text" />
</local:ValidateTime.Maximum>

If the validation works like you said you should be all set.

You can do the same thing with your EndTime TextBox if you want as well assuming you write a working rule for it

score 0 · Answer 2 · edited May 23 '17 at 11:45

0

You probably need to work around the fact that ValidationRules are not in the visual or logical trees, which causes bindings to DataContext, ElementName and RelativeSource to fail.

edited May 23 '17 at 11:45

Community

1
1

answered Mar 24 '16 at 05:35

H.B.

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score 0 · Answer 3 · answered Mar 30 '16 at 13:43

In my case

<local:RangeValidation ValidationStep="UpdatedValue"/>

helped. So you pass the DependencyObject as value(.dataitem) including your Datacontext and have no need to pass a parameter to the Validation. BR, Daniel

BTW credits not on mee, just found it but can't remember who gave the hint :)

Binding to a ValidationRule in WPF

3 Answers3