UITextField对象的方法状态是forControlEvents:UIControlEventEditingChanged

- (IBAction)textFieldDidChange:(UITextField *)sender {    if (![_paidPwdField.text hasPrefix:_paidPwdAgainField.text]) {        _hud = [MBProgressHUD showHUDAddedTo:[[UIApplication sharedApplication].windows lastObject] animated:YES];        _hud.userInteractionEnabled = NO;        _hud.mode = MBProgressHUDModeCustomView;        _hud.detailsLabelText = @"再次输入密码与上次输入密码不一致";        [_hud hide:YES afterDelay:1];            }}