- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField; // return NO to disallow editing. 返回NO 文本框不可编辑
- (void)textFieldDidBeginEditing:(UITextField *)textField; // became first responder 当前文本框变为第一响应者的时候触发这个事件
- (BOOL)textFieldShouldEndEditing:(UITextField *)textField; // return YES to allow editing to stop and to resign first responder status. NO to disallow the editing session to end
- (void)textFieldDidEndEditing:(UITextField *)textField; // may be called if forced even if shouldEndEditing returns NO (e.g. view removed from window) or endEditing:YES called
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string; // return NO to not change text
- (BOOL)textFieldShouldClear:(UITextField *)textField; // called when clear button pressed. return NO to ignore (no notifications)
- (BOOL)textFieldShouldReturn:(UITextField *)textField; // called when 'return' key pressed. return NO to ignore. 文本框点击键盘的上得return 键时调用。