当POP，push，dismiss，pressent连续调用的时候，要延迟会使用，

- (IBAction)goShoppingCartButtonAction:(id)sender

{

    [self.navigationController popToRootViewControllerAnimated:NO];

    [self performSelector:@selector(selectThirdTab) withObject:nil afterDelay:.3f];

}

- (void)selectThirdTab

{

    MSAppDelegate *appDelegate = (MSAppDelegate *)[[UIApplication sharedApplication] delegate];

    [appDelegate.tabBarController setSelectedIndex:3];

}

老大威武，afterDelay，