Notifications

UITextFieldTextDidBeginEditingNotification

UITextFieldTextDidChangeNotification

UITextFieldTextDidEndEditingNotification

委托事件

@protocol UITextFieldDelegate <NSObject>

@optional

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField;        // 返回 NO 则不许编辑

- (void)textFieldDidBeginEditing:(UITextField *)textField;           // became first responder

- (BOOL)textFieldShouldEndEditing:(UITextField *)textField;          // 返回 YES 允许结束并且
resign first responder status. 返回 NO 不许编辑状态结束

- (void)textFieldDidEndEditing:(UITextField *)textField;             // 上面返回 YES 后执行;上面
返回

NO 时有可能强制执行(e.g. view removed from window)

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range 
replacementString:(NSString *)string;   // 返回 NO 不改变

- (BOOL)textFieldShouldClear:(UITextField *)textField;               // clear button 事件,返回 NO 过
滤之

- (BOOL)textFieldShouldReturn:(UITextField *)textField;              // 'return' key 事件.返回 NO 过
滤之

@end