一尘不染

如何使用RX限制事件流?

c#

我想有效地限制事件流,以便在接收到第一个事件时调用我的委托,但是如果接收到后续事件,则不放一秒钟。该超时时间(1秒)到期后,如果接收到后续事件,则希望调用我的委托。

有使用Reactive Extensions做到这一点的简单方法吗?

样例代码:

static void Main(string[] args)
{
    Console.WriteLine("Running...");

    var generator = Observable
        .GenerateWithTime(1, x => x <= 100, x => x, x => TimeSpan.FromMilliseconds(1), x => x + 1)
        .Timestamp();

    var builder = new StringBuilder();

    generator
        .Sample(TimeSpan.FromSeconds(1))
        .Finally(() => Console.WriteLine(builder.ToString()))
        .Subscribe(feed =>
                   builder.AppendLine(string.Format("Observed {0:000}, generated at {1}, observed at {2}",
                                                    feed.Value,
                                                    feed.Timestamp.ToString("mm:ss.fff"),
                                                    DateTime.Now.ToString("mm:ss.fff"))));

    Console.ReadKey();
}

电流输出:

Running...
Observed 064, generated at 41:43.602, observed at 41:43.602
Observed 100, generated at 41:44.165, observed at 41:44.602

但我想观察一下(时间戳显然会改变)

Running...
Observed 001, generated at 41:43.602, observed at 41:43.602
....
Observed 100, generated at 41:44.165, observed at 41:44.602

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2020-05-19

共1个答案

一尘不染

这是我在RX论坛上获得的一些帮助:

这个想法是发行一系列“票”以激发原始顺序。这些“票证”因超时而被延迟,但不包括第一个票证,该票证将立即添加到票证序列中。当事件进入且有票证等待时,该事件会立即触发,否则会等到票证再触发。当它触发时,发出下一张票,依此类推…

为了将票证和原始事件结合起来,我们需要一个组合器。不幸的是,此处无法使用“标准”
.CombineLatest,因为它会在以前使用的票证和事件上触发。因此,我必须创建自己的组合器,该组合器基本上是经过过滤的.CombineLatest,它仅在组合中的两个元素均为“新鲜”时才触发-
之前从未返回过。我称之为.CombineVeryLatest又名.BrokenZip;)

使用.CombineVeryLatest,可以将上述想法实现为:

    public static IObservable<T> SampleResponsive<T>(
        this IObservable<T> source, TimeSpan delay)
    {
        return source.Publish(src =>
        {
            var fire = new Subject<T>();

            var whenCanFire = fire
                .Select(u => new Unit())
                .Delay(delay)
                .StartWith(new Unit());

            var subscription = src
                .CombineVeryLatest(whenCanFire, (x, flag) => x)
                .Subscribe(fire);

            return fire.Finally(subscription.Dispose);
        });
    }

    public static IObservable<TResult> CombineVeryLatest
        <TLeft, TRight, TResult>(this IObservable<TLeft> leftSource,
        IObservable<TRight> rightSource, Func<TLeft, TRight, TResult> selector)
    {
        var ls = leftSource.Select(x => new Used<TLeft>(x));
        var rs = rightSource.Select(x => new Used<TRight>(x));
        var cmb = ls.CombineLatest(rs, (x, y) => new { x, y });
        var fltCmb = cmb
            .Where(a => !(a.x.IsUsed || a.y.IsUsed))
            .Do(a => { a.x.IsUsed = true; a.y.IsUsed = true; });
        return fltCmb.Select(a => selector(a.x.Value, a.y.Value));
    }

    private class Used<T>
    {
        internal T Value { get; private set; }
        internal bool IsUsed { get; set; }

        internal Used(T value)
        {
            Value = value;
        }
    }

编辑:这是AndreasKöpf在论坛上提出的CombineVeryLatest的另一个更紧凑的变体:

public static IObservable<TResult> CombineVeryLatest
  <TLeft, TRight, TResult>(this IObservable<TLeft> leftSource,
  IObservable<TRight> rightSource, Func<TLeft, TRight, TResult> selector)
{
    return Observable.Defer(() =>
    {
        int l = -1, r = -1;
        return Observable.CombineLatest(
            leftSource.Select(Tuple.Create<TLeft, int>),
            rightSource.Select(Tuple.Create<TRight, int>),
                (x, y) => new { x, y })
            .Where(t => t.x.Item2 != l && t.y.Item2 != r)
            .Do(t => { l = t.x.Item2; r = t.y.Item2; })
            .Select(t => selector(t.x.Item1, t.y.Item1));
    });
}
2020-05-19