NotifyPropertyChanged when binding to itemsource of datagrid in Silverlight RIA

I have a textbox and a datagrid in a silverlight project. The textbox should be enabled if the item count in the datagrid is 0 or the sum of a field in the datagrids itemssource = 0.

I've bound the isEnabled value of the textbox to the datagrids ItemsSource.SourceCollection which gives me an IEnumerable. I've made a converter that converts this datamodel to bool.

When I open my silverlight pa开发者_JAVA百科ge and bind the datagrid, the converter runs and everything i working as expected, but nothing happens if i change the sum field or add/delete rows in the datagrid.

I'm guessing it has something to do with notify property changes on my datamodel, but I don't know.

Any thoughts on how to solve this?

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I asked similar question and as Luc answered you need have INotifyPropertyChanged event implementation, if not item changes will not happen. How to make a cell in a datagrid readonly based the content on another cell in SL4?

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Yes, when you bind to a sub property of an object then you need a PropertyChanged event of that specific property in order for the target to update its value.

In your example the ItemsSource needs to raise a PropertyChanged event of the property SourceCollection.

What you could do is bind to ItemsSource wich will be triggered and then in your converter use the Sourcecollection value.

eg:

    <sdk:DataGrid Name="dg" ItemsSource="{Binding}" AutoGenerateColumns="True" VerticalAlignment="Top"/>
    <TextBox Text="{Binding ElementName=dg, Path=ItemsSource.Count}" VerticalAlignment="Bottom" HorizontalAlignment="Right"/>

code:

        _items = new ObservableCollection<SomeClass>();
        _items.Add(new SomeClass() { Name = "a" });
        _items.Add(new SomeClass() { Name = "b" });
        _items.Add(new SomeClass() { Name = "c" });

        DataContext = _items;

    private void testButton_Click(object sender, RoutedEventArgs e)
    {
        _items.Add(new SomeClass(){Name = "ha"});

    }