Silverlight Binding - Binds when item is added but doesn't get updates

Question

I'm sorta at a loss to why this doesn't work considering I got it from working code, just added a new level of code, but here's what I have. Basically, when I bind the ViewModel to a list, the binding picks up when Items are added to a collection. However, if an update occurs to the item that is bound, it doesn't get updated. Basically, I have an ObservableCollection that contains a custom class with a string value. When that string value gets updated I need it to update the List.

Right now, when I debug, the list item does get updated correctly, but the UI doesn't reflect the change. If I set the bound item to a member variable and null it out then reset it to the right collection it will work, but not desired behavior.

Here is a mockup of the code, hopefully someone can tell me where I am wrong. Also, I've tried implementing INofityPropertyChanged at every level in the code below.

public class Class1
{
     public string ItemName;
}

public class Class2
{
     private Class2 _items;

     private Class2() //Singleton
     {
          _items = new ObservableCollection<Class1>();
     }

     public ObservableCollection<Class1> Items
     {
          get { return _items; }
          internal set 
          { 
               _items = value;
          }
     }
}

public class Class3
{

     private Class2 _Class2Instnace;

     private Class3()
     {
          _Class2Instnace = Class2.Instance;
     }

     public ObservableCollection<Class1> Items2
     {
          get {return _Class2Instnace.Items; }
     }
}

public class MyViewModel : INofityPropertyChanged
{
     private Class3 _myClass3;

     private MyViewModel()
     {
          _myClass3 = new Class3();
     }

     private BindingItems
     {
          get { return _myClass3.Items2; }  // Binds when adding items but not when a Class1.ItemName gets updated.
     }
}

I can see an attempt at a Singleton pattern here but the code actually posted is a little messed up. There is no static instance of Class2 nor a static Instance property. Not that it matters its unrelated to your problem. — AnthonyWJones
Yea, the singleton works, I just didn't feel like typing it all out. Figured if I said it was a singleton, you'd assume the rest of the code was there. I don't think that has anything to do with the issue. — dw.
@dw: For future reference its usually best to post short but complete code or to explicitly include comments to the effect that implementation details are missing. If the problem had be less obvious it could have been distracting making it hard to come to a correct answer. — AnthonyWJones

AnthonyWJones AnthonyWJones · Accepted Answer · 2010-04-01T15:48:35

The answer to your question is that Class1 needs to implement INotifyPropertyChanged.

public class Class1 : INotifyPropertyChanged
{
    private string _ItemName;
    public string ItemName
    {
       get { return _ItemName; }
       set
       {
         _ItemName = value;
         NotifyPropertyChanged("ItemName");
       }
    }

    private void NotifyPropertyChanged(string name)
    {
      if (PropertyChanged != null)
        PropertyChanged(this, new PropertyChangedEventArgs(name));
    }

    public event PropertyChangedEventHandler PropertyChanged;

}

Silverlight Binding - Binds when item is added but doesn't get updates

1 Answers