Question

I have one problem. i have dep. prop. of type List..

    public const string ValidationRulesPropertyName = "ValidationRules";


    public static List<ValidationRule> GetValidationRules(DependencyObject obj)
    {
        return (List<ValidationRule>)obj.GetValue(ValidationRulesProperty);
    }


    public static void SetValidationRules(DependencyObject obj, List<ValidationRule> value)
    {
        obj.SetValue(ValidationRulesProperty, value);
    }

    public static readonly DependencyProperty ValidationRulesProperty = DependencyProperty.RegisterAttached(
    ValidationRulesPropertyName,
    typeof(List<ValidationRule>),
    typeof(CustomGrid),
    new PropertyMetadata(new List<ValidationRule>()));

And now if I set in my custom grid some textboxes and inside one list of ValidationRules

<Grid>
<TextBox x:Name="txt1">
<ValidationRules>
<Validation:SomeValidationRule/>
</ValidationRule>
</TextBox>
<TextBox x:Name="txt2"/>
</Grid>

Ok. Now the problem is when I try to get list of rules for some element.. If have instances of txt1 and txt2 whe I get validation rules they both return instance of SomeValidationRule.

Grid.GetValidationRules(txt1Instance);

and

Grid.GetValidationRules(txt2Instance);

return same list.

Even if try

Grid.GetValidationRules(new TextBox());

I get the same list with SomeValidationRule as only alement in list. So that is strange. If I manually set list to some element then that element have that list that i set but all others element have list that i set up in xaml only for txt1.

Any idea? Thanks!

Answer 1

Try this modification:-

    public const string ValidationRulesPropertyName = "ValidationRules";

    public static List<ValidationRule> GetValidationRules(DependencyObject obj)
    {
        object result = obj.ReadLocalValue(ValidationRulesProperty);
        if (result == DependencyProperty.UnsetValue)
        {
            result = new List<ValidationRule>();
            obj.SetValue(ValidationRulesProperty, result);
        }
        return (List<ValidationRule>)result;
    }


    public static void SetValidationRules(DependencyObject obj, List<ValidationRule> value)
    {
        obj.SetValue(ValidationRulesProperty, value);
    }

    public static readonly DependencyProperty ValidationRulesProperty = DependencyProperty.RegisterAttached(
    ValidationRulesPropertyName,
    typeof(List<ValidationRule>),
    typeof(CustomGrid), null);

This code removes the single instance of List created in the Metadata and defers the creation of a list until the first time GetValidationRules is called which in turn creates a List if one hasn’t already been created.

When using PropertyMetaData only immutable types should be used as a default value.