I need to fill textboxes depending on the item selected in a combobox. I fill combo async and in Completed event I have the following code

combo.ItemsSource = e.Result;
combo.DisplayMemberPath = "Name";
combo.SelectedIndex = -1;

Then in the SelectionChanged event of the combo, I catch the selected object

MyClass mc= ((ComboBox)sender).SelectedItem as MyClass;
tbxName.Text = mc.Name;
...

However, when I load the project and select any event for the 1st time, NOTHING happens. Every other time (2nd, 3rd, nth) the data is correctly caught and displayed.

So I need to know why the combo doesn't catch the first selection? That's the reason I have the code combo.SelectedIndex = -1 (when the app loads, combo is empty - selection -1 works).