当我使用[UITabBarController setSelectedIndex：]和-popToRootViewControllerAnimated：时，viewController不会取消分配

Question

当我使用[UITabBarController setSelectedIndex：]和-popToRootViewControllerAnimated：时，例如：

- (void)backViewControllerAnimation:(BOOL)animation {
    if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
        self.navigationController.interactivePopGestureRecognizer.enabled = YES;
    }

    [OLTabBarController.defaultTabBar.tabBarController setSelectedIndex:0];
    [self.navigationController popToRootViewControllerAnimated:YES];
}

viewController不会取消分配，但是如果我删除[UITabBarController setSelectedIndex：0]，就像这样：

- (void)backViewControllerAnimation:(BOOL)animation {
    if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
        self.navigationController.interactivePopGestureRecognizer.enabled = YES;
    }

    [self.navigationController popToRootViewControllerAnimated:YES];
}

viewController可以取消分配，我想知道发生了什么，我需要-setSelectedIndex：方法，如何使viewController执行-dealloc方法？