UITextView通知 UITextViewTextDidChangeNotification 键盘通知 键盘的frame发生改变时发出的通知（位置和尺寸） UIKeyboardWillChangeFrameNotification UIKeyboardDidChangeFrameNotification 键盘显示时发出的通知 UIKeyboardWillShowNotification UIKeyboardDidShowNotification 键盘隐藏时发出的通知 UIKeyboardWillHideNotification