c# - Rx.NET "gate"运算符

Question

[注意:如果重要的话，我正在使用 3.1。另外，我在 codereview 上问过这个问题，但到目前为止还没有回复。]

我需要一个运算符来允许 bool 值流充当另一个流的门(当门流为真时让值通过，当门流为假时丢弃它们)。我通常会使用 Switch 来实现此目的，但如果源流很冷，它会继续重新创建它，这是我不希望的。

我还想自己清理，以便在源或门完成时结果也完成。

public static IObservable<T> When<T>(this IObservable<T> source, IObservable<bool> gate)
{
    var s = source.Publish().RefCount();
    var g = gate.Publish().RefCount();

    var sourceCompleted = s.TakeLast(1).DefaultIfEmpty().Select(_ => Unit.Default);
    var gateCompleted = g.TakeLast(1).DefaultIfEmpty().Select(_ => Unit.Default);

    var anyCompleted = Observable.Amb(sourceCompleted, gateCompleted);

    var flag = false;
    g.TakeUntil(anyCompleted).Subscribe(value => flag = value);

    return s.Where(_ => flag).TakeUntil(anyCompleted);
}

除了整体冗长之外，我不喜欢订阅门，即使结果从未订阅(在这种情况下，该运算符应该是无操作)。有没有办法摆脱订阅？

我也尝试过这种实现，但是当涉及到自身清理时，情况更糟:

return Observable.Create<T>(
    o =>
    {
        var flag = false;
        gate.Subscribe(value => flag = value);

        return source.Subscribe(
            value =>
            {
                if (flag) o.OnNext(value);
            });
    });

这些是我用来检查实现情况的测试:

[TestMethod]
public void TestMethod1()
{
    var output = new List<int>();

    var source = new Subject<int>();
    var gate = new Subject<bool>();

    var result = source.When(gate);
    result.Subscribe(output.Add, () => output.Add(-1));

    // the gate starts with false, so the source events are ignored
    source.OnNext(1);
    source.OnNext(2);
    source.OnNext(3);
    CollectionAssert.AreEqual(new int[0], output);

    // setting the gate to true will let the source events pass
    gate.OnNext(true);
    source.OnNext(4);
    CollectionAssert.AreEqual(new[] { 4 }, output);
    source.OnNext(5);
    CollectionAssert.AreEqual(new[] { 4, 5 }, output);

    // setting the gate to false stops source events from propagating again
    gate.OnNext(false);
    source.OnNext(6);
    source.OnNext(7);
    CollectionAssert.AreEqual(new[] { 4, 5 }, output);

    // completing the source also completes the result
    source.OnCompleted();
    CollectionAssert.AreEqual(new[] { 4, 5, -1 }, output);
}

[TestMethod]
public void TestMethod2()
{
    // completing the gate also completes the result
    var output = new List<int>();

    var source = new Subject<int>();
    var gate = new Subject<bool>();

    var result = source.When(gate);
    result.Subscribe(output.Add, () => output.Add(-1));

    gate.OnCompleted();
    CollectionAssert.AreEqual(new[] { -1 }, output);
}

Answer 1

更新:当门终止时，此操作也会终止。我在复制/粘贴中错过了 TestMethod2:

    return gate.Publish(_gate => source
        .WithLatestFrom(_gate.StartWith(false), (value, b) => (value, b))
        .Where(t => t.b)
        .Select(t => t.value)
        .TakeUntil(_gate.IgnoreElements().Materialize()
    ));

---

这通过了 您的测试 TestMethod1，当门可观察到时它不会终止。

public static IObservable<T> When<T>(this IObservable<T> source, IObservable<bool> gate)
{
    return source
        .WithLatestFrom(gate.StartWith(false), (value, b) => (value, b))
        .Where(t => t.b)
        .Select(t => t.value);
}