反应式扩展:如何忽略短状态更改

Question

我想从我的 Xamarin 应用观察互联网连接的状态变化。我使用连接插件，它提供了一个连接更改事件，我将其转换为可观察量。这工作正常。

问题是当手机从3G切换到4G时，我想忽略一个短暂的断开连接。

到目前为止，我尝试使用 Throttle 和 Distinct 直到更改，但没有运气，因为即使状态与断开连接之前相同，我也总是得到一个值。

到目前为止，我尝试了这个：

var connectionEvent = Observable.FromEventPattern<ConnectivityChangedEventHandler, ConnectivityChangedEventArgs>( handler => handler.Invoke, h => CrossConnectivity.Current.ConnectivityChanged += h, h => CrossConnectivity.Current.ConnectivityChanged -= h) .Select(x => x.EventArgs.IsConnected) .Throttle(TimeSpan.FromSeconds(5)) .DistinctUntilChanged()
.StartWith(CrossConnectivity.Current.IsConnected) .Publish();

Answer 1

很难

弄清楚"当我不想开火时东西被解雇"发生了什么。幸运的是，Rx有一些强大的测试支持。下面是一些测试代码（使用 Nuget Install-Package Microsoft.Reactive.Testing）。 source表示来自 Android API 的噪音。 target是你在其上的一组运算符。 结果expectedResults：

TestScheduler ts = new TestScheduler();
var crossConnectivity_Current_IsConnected = true;
var source = ts.CreateHotObservable<bool>(
    new Recorded<Notification<bool>>(200.MsTicks(), Notification.CreateOnNext(false)),
    new Recorded<Notification<bool>>(300.MsTicks(), Notification.CreateOnNext(true)),
    new Recorded<Notification<bool>>(5550.MsTicks(), Notification.CreateOnNext(false)),
    new Recorded<Notification<bool>>(5600.MsTicks(), Notification.CreateOnNext(true)),
    new Recorded<Notification<bool>>(5800.MsTicks(), Notification.CreateOnNext(false)),
    new Recorded<Notification<bool>>(7700.MsTicks(), Notification.CreateOnNext(true)),
    new Recorded<Notification<bool>>(7800.MsTicks(), Notification.CreateOnNext(false)),
    new Recorded<Notification<bool>>(13000.MsTicks(), Notification.CreateOnNext(true))
);
var target = source
    .Throttle(TimeSpan.FromSeconds(5), ts)
    .DistinctUntilChanged()
    .StartWith(crossConnectivity_Current_IsConnected);
var expectedResults = ts.CreateHotObservable<bool>(
    new Recorded<Notification<bool>>(0.MsTicks(), Notification.CreateOnNext(true)),
    new Recorded<Notification<bool>>(5300.MsTicks(), Notification.CreateOnNext(true)),
    new Recorded<Notification<bool>>(12800.MsTicks(), Notification.CreateOnNext(false)),
    new Recorded<Notification<bool>>(18000.MsTicks(), Notification.CreateOnNext(true))
);

我看到的唯一问题是 5300 的通知。您可以通过对运算符进行一些重新排序来摆脱它。看看我的target2：

var target2 = source
    .Throttle(TimeSpan.FromSeconds(5), ts)
    .StartWith(crossConnectivity_Current_IsConnected)
    .DistinctUntilChanged()
    ;
var expectedResults2 = ts.CreateHotObservable<bool>(
    new Recorded<Notification<bool>>(0.MsTicks(), Notification.CreateOnNext(true)),
    new Recorded<Notification<bool>>(12800.MsTicks(), Notification.CreateOnNext(false)),
    new Recorded<Notification<bool>>(18000.MsTicks(), Notification.CreateOnNext(true))
);

。如果你想运行测试，这里是运行器代码。

var observer = ts.CreateObserver<bool>();
target.Subscribe(observer);
var observer2 = ts.CreateObserver<bool>();
target2.Subscribe(observer2);
ts.Start();
ReactiveAssert.AreElementsEqual(expectedResults.Messages, observer.Messages);
ReactiveAssert.AreElementsEqual(expectedResults2.Messages, observer2.Messages);

。您将需要这个类

public static class Extensions
{
    public static long MsTicks(this int i)
    {
        return TimeSpan.FromMilliseconds(i).Ticks;
    }
}

如果这不能解决您的问题，请增加source以描述它何时/如何发生。