在TPL任务运行时如何显示iOS网络指示器？

我创建了这个类,将NetworkActivityIndi​​catorVisible包装成一对进入/离开方法.

public static class NetworkInDicator
{
    static int _counter;

    public static void EnterActivity ()
    {
        Interlocked.Increment (ref _counter);
        refreshInDicator ();
    }

    public static void LeaveActivity ()
    {
        Interlocked.Decrement (ref _counter);
        refreshInDicator ();
    }

    public static void Attach@R_829_10586@sk (Task task)
    {
        if (task.IsCanceled || task.IsCanceled || task.IsFaulted)
            return;

        EnterActivity ();
        task.ConTinueWith (t => {
            LeaveActivity ();
        });
    }

    static void refreshInDicator ()
    {
        UIApplication.SharedApplication.NetworkActivityInDicatorVisible =
            (_counter > 0);
    }
}

然后我为方便起见添加了两个扩展方法：

public static class TaskExtensions
{
    public static Task WithNetworkInDicator (this Task task)
    {
        NetworkInDicator.Attach@R_829_10586@sk (task);
        return task;
    }

    public static Task<TResult> WithNetworkInDicator<TResult> (this Task<TResult> task)
    {
        NetworkInDicator.Attach@R_829_10586@sk (task);
        return task;
    }
}

我是如何包装它的：

var task = Api.QueryNotifications (AuthManager.CurrentProfile.Id,NotificationType.All,until,cached)
    .WithNetworkInDicator ();

然后我像往常一样使用任务.