NullReferenceException on TreeView node deselect

Question

I have two TreeViews in my program that deal with SelectedItemChanged in the same way. The problem is that one works fine and the other one throws a NullReferenceException. The exception gets thrown in one of the trees when a node is deselected...

How SelectedItemChanged is handled for both trees in the code-behind:

//How *ViewModel* is declared...
public DatabaseViewModel ViewModel { get { return DataContext as DatabaseViewModel; } }

//Gets selected item in TreeView
private void Tree_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e) 
{
     var data = e.NewValue as TreeModel;
     ViewModel.Tree.SelectedItem = data;
}

This is basically what happens:

-A node in the problem tree is selected

-Next, a node in the well-behaved tree is selected

-A NullReferenceException is then thrown on the line: ViewModel.Tree.SelectedItem = data. in the problem tree's code-behind. The exception says: "Object reference not set to an instance of an object".

What is going wrong here and how can I fix it? Thank you.

*Note: I'd just like to point out that this does not happen for the other tree.

Have you verified that the DataContext in the bad case is actually an instance of DatabaseViewModel? Set a breakpoint on the line where the exception is thrown, then you can check the DataContext. — foosburger, Nov 01 '13 at 20:37

score 1 · Accepted Answer · answered Nov 01 '13 at 20:36

1

Try this :

//Gets selected item in TreeView
private void Tree_SelectedItemChanged(object sender,RoutedPropertyChangedEventArgs<object> e) 
{
     var data = e.NewValue as TreeModel;
     if(data!=null)
     ViewModel.Tree.SelectedItem = data;
}

answered Nov 01 '13 at 20:36

Sudhakar Tillapudi

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This is almost so simple that I probably should have thought of it. Regardless, thanks it worked fine! =) – Eric after dark Nov 01 '13 at 20:45

NullReferenceException on TreeView node deselect

1 Answers1