Question

I have a class called ObservableCollectionWithValidState that serves to notify itself when an of it’s child objects break a validation rule.

Class:

child
child  <== violated a passed in Predicate and is now invalid.
child

When this happens I would love to have a DependencyProperty on this class that I can set which can be bound to.

The problem is that my class extends ObservableCollection<T> but I can’t see how to get DependencyObject into the picture.

I am pasting the initial declaration of the class along with an example of the property I would like to add (this will not work unless I can extend DependencyProperty).

public class ObservableCollectionWithIsValidState<T> : ObservableCollection<T> where T : INotifyPropertyChanged,
{
    public static readonly DependencyProperty IsValidPropertyProperty = DependencyProperty.Register("IsValid", typeof(bool), typeof(ObservableCollectionWithIsValidState<T>), new PropertyMetadata(true));

    public bool IsValid
    {
       get { return (bool)GetValue(IsValidPropertyProperty); }
       set { SetValue(IsValidPropertyProperty, value); }
    }
}

My two questions:

1. Is this possible?
2. If it’s not possible is there an alternate implementation you can suggest?

Answer 1

It is not possible. DependencyProperty can only be created in class that extends DependencyObject.

From MSDN-DependendyObject

DependencyObject services and characteristics include the following:
Dependency property hosting support.

• You register a dependency property by calling the Register method, and storing the method’s return value as a public static field in your class.

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Is this possible?

Not Possible

If it’s not possible is there an alternate implementation you can suggest?

Use INotifyPropertyChanged, and IDataErrorInfo with normal CLR property for Property validation. Example