其中,第8行代码的意义在于移除之前可能订阅过的KeyPress事件,防止同一事件被多次订阅
MSDN详细说明:
The DataGridView control hosts one editing control at a time, and reuses the editing control whenever the cell type does not change between edits. When attaching event-handlers to the editing control, you must therefore take precautions to avoid attaching the same handler multiple times. To avoid this problem, remove the handler from the event before you attach the handler to the event. This will prevent duplication if the handler is already attached to the event, but will have no effect otherwise. For more information, see the example code in the DataGridViewComboBoxEditingControl class overview.