wpf observableCollection
- by Asha
I have an ObservableCollection which is dataContext for my treeview when I try to remove an Item from ObservableCollection I will get an error that Object reference not set to an instance of an object .
can you please tell me why this error is happening and what is the solution
thanks
EDIT 1: The code is something like :
class MyClass : INotifyPropertyChanged
{
//my class code here
}
public partial class UC_myUserControl : UserControl
{
private ObservableCollection<MyClass> myCollection = new ObservableCollection<MyClass>();
private void UserControl_Loaded(object sender, RoutedEventArgs e)
{
myCollection.add(new myClass);
myTreeView.DataContext = myCollection ;
}
private void deleteItem()
{
myCollection.RemoveAt(0);
//after removing I get error Which I guess should be something related
//to interface update but I don't know how can I solve it
}
}
Exception Detail :
System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="PresentationFramework"
EDIT 3: I have a style which is for my treeitem to keep the treeitems expanded
<Style TargetType="TreeViewItem">
<Setter Property="IsExpanded" Value="True" />
</Style>
and with commenting this part I wont get any error !!!
Now I want to change my question to why having this style is causing error ?
