- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;
if ([string isEqualToString:@""])//如果string是空白的话就是删除。
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;
if ([string isEqualToString:@""])//如果string是空白的话就是删除。