unhooks

This line unhooks the DocumentChange event so it is not fired during the call to Quit.

此代码行解除了DocumentChange事件的挂钩，这样该事件就不会在调用Quit期间引发了。

when overridden in a derived class , unhooks events from the current data source.

在派生类中重写后，从当前数据源卸载事件。