The property setter TabItem.IsSelected compares new values with Button.IsPressed (via its getter) and early-outs if the value is unchanged, bypassing the SelectedChanged event.
When clicking on a tab item to select it, the Button.IsPressed value will always be the same as the value received by the property since they originate from the same source.
On deselect however, the SelectedChanged event will fire due to the setter logic in Selector.SelectedItem calling _selectedItem.IsSelected = false; on the previous item.
rds1983
commented
3 years ago
The property setter
TabItem.IsSelectedcompares new values withButton.IsPressed(via its getter) and early-outs if the value is unchanged, bypassing theSelectedChangedevent. When clicking on a tab item to select it, theButton.IsPressedvalue will always be the same as the value received by the property since they originate from the same source.On deselect however, the
SelectedChangedevent will fire due to the setter logic inSelector.SelectedItemcalling_selectedItem.IsSelected = false;on the previous item.