开发时候，当我们输入的时候，键盘通知的调用顺序为：

keyboardWillChangeFrame

keyboardWillShow

//  这里会调用很多次数

keyboardDidChangeFrame

keyboardDidChangeFrame

keyboardDidChangeFrame

keyboardDidShow

这个时候点击完成

keyboardWillChangeFrame

keyboardWillHide

//  这里会调用很多次数

keyboardDidChangeFrame

keyboardDidChangeFrame

keyboardDidChangeFrame

keyboardDidHide

通知里面包含的信息:

 userInfo {

UIKeyboardAnimationCurveUserInfoKey = 7;

UIKeyboardAnimationDurationUserInfoKey = "0.25";

UIKeyboardBoundsUserInfoKey = "NSRect: {{0, 0}, {414, 271}}";

UIKeyboardCenterBeginUserInfoKey = "NSPoint: {207, 600.5}";

UIKeyboardCenterEndUserInfoKey = "NSPoint: {207, 871.5}";

UIKeyboardFrameBeginUserInfoKey = "NSRect: {{0, 465}, {414, 271}}";

UIKeyboardFrameEndUserInfoKey = "NSRect: {{0, 736}, {414, 271}}";

UIKeyboardIsLocalUserInfoKey = 1;

}