I have a CheckBox chkAddToGroup
which activates this ComboBox cmbGroup
.
If chkAddToGroup
is being checked the following happens:
ObservableCollection<Group> groupColl = new ObservableCollection<Group>() { };
foreach (Group g in GroupHandler.GroupList)
{
groupColl.Add(g);
}
cmbGroup.ItemsSource = groupColl;
cmbOrganisation.SelectedIndex = 0;
cmbGroup.IsEnabled = true;
As you can see cmbGroup
is attached to groupColl
(DisplayMemberPath
is set in an external Style
).
The problem occurs if I try to reset my form. Therefor I have a Button btnReset
.
If the user clicks on btnReset
the application does this:
chkAddToGroup_Unchecked(this, null);
In chkAddToGroup_Unchecked(object sender, RoutedEventArgs e)
following happens then:
private void chkAddToGroup_Unchecked(object sender, RoutedEventArgs e)
{
cmbGroup.ItemsSource = null;
cmbGroup.IsEnabled = false;
cmbGroupRole.ItemsSource = null;
cmbGroupRole.IsEnabled = false;
}
As you can see I set ItemsSource = null
in order to clear the combobox. (don't know any other way atm)
If the user didn't check the checkbox before hitting the reset button then nothing special happens.
But if the user did check the checkbox and selected an item then there is a NullReferenceException
as soon as the application tries to execute cmbGroup.ItemsSource = null;
Why does this happen? Any idea?