Rx基礎

時間 2020-02-01

標籤基礎简体版

原文原文鏈接

要在應用中安裝一個 NuGet 包 System.Reactive。編程

Rx 能夠認做是 LINQ to events（基於 IObservable<T>）
全部的 LINQ 操做均可以在 Rx 中使用。
從概念上看，過濾（Where）、投影（Select）等簡單操做，和其餘 LINQ 提供者的操做是同樣的

1. 轉換.NET事件

1.1. 進度通知

public static void ProgressRun()
{
    var progress = new Progress<int>();
    var progressReports = Observable.FromEventPattern<int>(
        handler => progress.ProgressChanged += handler,
        handler => progress.ProgressChanged -= handler)
        //.Where(u => u.EventArgs % 2 == 0)
        ;
    progressReports.Subscribe(data => Console.WriteLine($"OnNext:{data.EventArgs},ThreadId:{Thread.CurrentThread.ManagedThreadId}."));

    Reports(progress);
}

private static void Reports(IProgress<int> progress)
{
    System.Console.WriteLine($"Reporting ThreadId:{Thread.CurrentThread.ManagedThreadId}.");
    for (int i = 0; i < 10; i++)
    {
        progress.Report(i);
    }
    System.Console.WriteLine($"Reported ThreadId:{Thread.CurrentThread.ManagedThreadId}.");
}

輸出:併發

Reporting ThreadId:1.
Reported ThreadId:1.
OnNext:5,ThreadId:9.
OnNext:0,ThreadId:4.
OnNext:6,ThreadId:10.
OnNext:1,ThreadId:5.
OnNext:2,ThreadId:6.
OnNext:4,ThreadId:8.
OnNext:3,ThreadId:7.
OnNext:7,ThreadId:11.
OnNext:9,ThreadId:13.
OnNext:8,ThreadId:12.

1.2. 定時器示例

public static void TimerRun()
{
    var timer = new System.Timers.Timer(interval: 300) { Enabled = true };
    var ticks = Observable.FromEventPattern<ElapsedEventHandler, ElapsedEventArgs>(
        handler => (s, a) => handler(s, a),
        handler => timer.Elapsed += handler,
        handler => timer.Elapsed -= handler);
    ticks.Subscribe(data => Console.WriteLine($"OnNext:{data.EventArgs.SignalTime.Millisecond}, ThreadId:{Thread.CurrentThread.ManagedThreadId}."));
    System.Console.WriteLine($"Timer start ThreadId:{Thread.CurrentThread.ManagedThreadId}.");
    timer.Start();
    Thread.Sleep(2000);
    timer.Stop();
    System.Console.WriteLine($"Timer stop ThreadId:{Thread.CurrentThread.ManagedThreadId}.");
}

輸出:ui

Timer start ThreadId:1.
OnNext:473, ThreadId:4.
OnNext:772, ThreadId:5.
OnNext:73, ThreadId:5.
OnNext:373, ThreadId:5.
OnNext:673, ThreadId:5.
OnNext:975, ThreadId:5.
Timer stop ThreadId:1.

1.3. 錯誤傳遞

public static void ObErrorRun()
{
    var tcs = new TaskCompletionSource<string>();
    var client = new WebClient();
    var downloadedStrings = Observable.FromEventPattern(client,
    "DownloadStringCompleted"); downloadedStrings.Subscribe(
    data =>
    {
        var eventArgs = (DownloadStringCompletedEventArgs)data.EventArgs;
        if (eventArgs.Error != null)
        {
            Console.WriteLine("OnNext: (Error) " + eventArgs.Error.GetType());
        }
        else
        {
            Console.WriteLine("OnNext: " + eventArgs.Result);
        }
    },
    ex => Console.WriteLine("OnError: " + ex.GetType()),
    () => Console.WriteLine("OnCompleted"));
    client.DownloadStringAsync(new Uri("http://invalid.example.com/"));
    //client.DownloadStringAsync(new Uri("http://www.baidu.com/"));
    Thread.Sleep(3000);
}

輸出:.net

OnNext: (Error) System.Net.WebException

把事件封裝進 Observable 對象後，每次引起該事件都會調用 OnNext 。在處理 AsyncCompletedEventArgs 時會發生使人奇怪的現象，全部的異常信息都是經過數據形式傳遞的(OnNext)，而不是經過錯誤傳遞(OnError)。線程

2. 發通知給上下文

如 UI 元素只能被它所屬的 UI 線程控制，所以，若是要根據 Rx 的通知來修改 UI，就應該把通知「轉移」到 UI 線程。code

可使用 ObserveOn 把通知移動到一個線程池線程，在那裏進行計算，而後再把表示結果的通知返回給 UI 線程
經過同步上下文切換實現

public delegate void HelloEventHandler(object sender, HelloEventArgs e);
public class HelloEventArgs : EventArgs
{
    public string Name { get; set; }
    public HelloEventArgs(string name)
    {
        Name = name;
    }
    public int SayHello()
    {
        System.Console.WriteLine(Name + " Hello.");
        return DateTime.Now.Millisecond;
    }
}

public static event HelloEventHandler HelloHandlerEvent;
public static void ObservableEventRun()
{
    IDisposable ob = null;
    var task = Task.Run(() =>
    {
        Thread.Sleep(500);
        HelloHandlerEvent?.Invoke(new object(), new HelloEventArgs("lilei"));
        HelloHandlerEvent?.Invoke(new object(), new HelloEventArgs("HanMeimei"));
        HelloHandlerEvent?.Invoke(new object(), new HelloEventArgs("Tom"));
        HelloHandlerEvent?.Invoke(new object(), new HelloEventArgs("Jerry"));
        Thread.Sleep(2000);
        ob?.Dispose();
        HelloHandlerEvent?.Invoke(new object(), new HelloEventArgs("NoConsole")); // 因爲
    });
    // AsyncContext 好比就是 UI上下文
    AsyncContext.Run(() =>
    {
        var uiContext = SynchronizationContext.Current;
        Console.WriteLine("UI thread is " + Environment.CurrentManagedThreadId);                                                                           //Observable.FromEvent()

        ob = Observable.FromEventPattern<HelloEventHandler, HelloEventArgs>(
            handler => (s, a) => handler.Invoke(s, a), handler => HelloHandlerEvent += handler, handler => HelloHandlerEvent -= handler)
        .Select(evt => evt.EventArgs.SayHello()).ObserveOn(Scheduler.Default)
        .Select(s =>
         {
            // 複雜的計算過程。
            Thread.Sleep(100);
            var result = s;
            Console.WriteLine("Now Millisecond result " + result + " on thread " + Environment.CurrentManagedThreadId);
            return result;
         })
        .ObserveOn(uiContext)
        .Subscribe(s => Console.WriteLine("Subscribe Result " + s + " on thread " + Environment.CurrentManagedThreadId));
        //此處不能 task.Wait(); ，會和 Subscribe 中的委託發生死鎖
        System.Console.WriteLine("AsyncContext.Run Done on thread " + Environment.CurrentManagedThreadId);
    });
    task.Wait();
}

輸出:htm

UI thread is 1
AsyncContext.Run Done on thread 1
lilei Hello.
HanMeimei Hello.
Tom Hello.
Jerry Hello.
Now Millisecond result 36 on thread 6
Subscribe Result 36 on thread 1
Now Millisecond result 44 on thread 6
Subscribe Result 44 on thread 1
Now Millisecond result 44 on thread 6
Subscribe Result 44 on thread 1
Now Millisecond result 44 on thread 6
Subscribe Result 44 on thread 1

3. 用窗口和緩衝對事件分組

下面的例子使用 Interval ，每秒建立 1 個 OnNext 通知，而後, 使用 Buffer , 每 2 個通知作一次緩衝：對象

public static void BufferRun()
{
    System.Console.WriteLine($"Buffer start ThreadId:{Thread.CurrentThread.ManagedThreadId}.");

    var ob = Observable.Interval(TimeSpan.FromMilliseconds(10))
     .Buffer(2)
     .Subscribe(x => Console.WriteLine($"{DateTime.Now.Millisecond}: Got {string.Join(",", x)}({Thread.CurrentThread.ManagedThreadId})"));
    Thread.Sleep(100);
    ob.Dispose();
    System.Console.WriteLine($"Buffer end ThreadId:{Thread.CurrentThread.ManagedThreadId}.");
}

輸出:事件

Buffer start ThreadId:1.
459: Got 0,1(5)
478: Got 2,3(5)
498: Got 4,5(5)
516: Got 6,7(5)
536: Got 8,9(5)
Buffer end ThreadId:1.

下面的例子有些相似，使用 Window 建立一些事件組，每組包含 2 個事件：

public static void WindowRun()
{
    System.Console.WriteLine($"Window start ThreadId:{Thread.CurrentThread.ManagedThreadId}.");
    var ob = Observable.Interval(TimeSpan.FromMilliseconds(10))
    .Window(2)
    .Subscribe(group =>
    {
        Console.WriteLine($"{DateTime.Now.Millisecond}: Starting new group({Thread.CurrentThread.ManagedThreadId})");
        group.Subscribe(x => Console.WriteLine($"{DateTime.Now.Millisecond}: Saw {x},(TID:{Thread.CurrentThread.ManagedThreadId})"),
            () => Console.WriteLine($"{DateTime.Now.Millisecond}: Ending group"));
    });
    Thread.Sleep(100);
    ob.Dispose();
    System.Console.WriteLine($"Window end ThreadId:{Thread.CurrentThread.ManagedThreadId}.");

}

輸出:

Window start ThreadId:1.
959: Starting new group(1)
987: Saw 0,(TID:4)
991: Saw 1,(TID:4)
992: Ending group
994: Starting new group(4)
0: Saw 2,(TID:4)
11: Saw 3,(TID:4)
11: Ending group
11: Starting new group(4)
21: Saw 4,(TID:4)
30: Saw 5,(TID:4)
30: Ending group
30: Starting new group(4)
40: Saw 6,(TID:4)
50: Saw 7,(TID:4)
50: Ending group
51: Starting new group(4)
60: Saw 8,(TID:4)
70: Saw 9,(TID:4)
70: Ending group
70: Starting new group(4)
Window end ThreadId:1.

這幾個例子說明了 Buffer 和 Window 的區別:

Buffer 等待組內的全部事件，而後把全部事件做爲一個集合發佈
Window 用一樣的方法進行分組，但它是在每一個事件到達時就發佈

4. 用限流和抽樣抑制事件流

4.1. Throttle

下面的例子也是監視鼠標移動，但使用了 Throttle ，在鼠標保持靜止 1 秒後才報告最近一條移動事件。

public delegate void MouseEventHandler(object sender, MouseEventArgs e);
public class MouseEventArgs : EventArgs
{
    public (int, int) XY { get; set; }
    public MouseEventArgs((int, int) xy)
    {
        XY = xy;
    }
    public (int, int) GetPosition()
    {
        return XY;
    }
}

public static event MouseEventHandler MouseMove;
public static void ThrottleRun()
{
    IDisposable ob = null;
    var task = Task.Run(() =>
    {
        Thread.Sleep(200);
        //不觸發
        MouseMoveProcess((1, 1));
        MouseMoveProcess((1, 11));
        MouseMoveProcess((1, 111));
        MouseMoveProcess((1, 1111));
        //觸發
        MouseMoveProcess((2, 2), 2000);
        //超時結束
        MouseMoveProcess((2, 22));
        ob?.Dispose();
    });

    ob = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>(
        handler => (s, a) => handler(s, a),
        handler => MouseMove += handler,
        handler => MouseMove -= handler)
    .Select(x => x.EventArgs.GetPosition())
    .Throttle(TimeSpan.FromMilliseconds(500))
    .Subscribe(x => Console.WriteLine($"{DateTime.Now.Millisecond}: Saw {x.Item1},{x.Item2}"));

    task.Wait();
}

private static void MouseMoveProcess((int, int) xy, int sleepMillsecond = 200)
{
    System.Console.WriteLine($"Mouse Move {xy.Item1},{xy.Item2},After sleep {sleepMillsecond}.");
    MouseMove?.Invoke(new object(), new MouseEventArgs(xy));
    Thread.Sleep(sleepMillsecond);
}

輸出:

Mouse Move 1,1,After sleep 200.
Mouse Move 1,11,After sleep 200.
Mouse Move 1,111,After sleep 200.
Mouse Move 1,1111,After sleep 200.
Mouse Move 2,2,After sleep 2000.
251: Saw 2,2
Mouse Move 2,22,After sleep 200.

Throttle 經常使用於相似「文本框自動填充」這樣的場合

用戶在文本框中輸入文字，當他中止輸入時，才須要進行真正的檢索。

4.2. Sample

爲抑制快速運動的事件序列, Sample 創建了一個有規律的超時時間段，每一個時間段結束時，它就發佈該時間段內最後的一條數據。若是這個時間段沒有數據，就不發佈。

每隔一秒採樣一次

public static void SampleRun()
{
    IDisposable ob = null;
    var task = Task.Run(() =>
    {
        Thread.Sleep(200);
        //不觸發
        MouseMoveProcess((1, 1));
        MouseMoveProcess((1, 11));
        MouseMoveProcess((1, 111));
        MouseMoveProcess((1, 1111));
        //觸發
        MouseMoveProcess((2, 2), 2000);
        //超時結束
        MouseMoveProcess((2, 22));
        ob?.Dispose();
    });

    ob = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>(
        handler => (s, a) => handler(s, a),
        handler => MouseMove += handler,
        handler => MouseMove -= handler)
    .Select(x => x.EventArgs.GetPosition())
    .Sample(TimeSpan.FromMilliseconds(500))
    .Subscribe(x => Console.WriteLine($"{DateTime.Now.Millisecond}: Saw {x.Item1},{x.Item2}"));

    task.Wait();
}

輸出:

Mouse Move 1,1,After sleep 200.
Mouse Move 1,11,After sleep 200.
498: Saw 1,11
Mouse Move 1,111,After sleep 200.
Mouse Move 1,1111,After sleep 200.
Mouse Move 2,2,After sleep 2000.
991: Saw 2,2
Mouse Move 2,22,After sleep 200.
992: Saw 2,22

Throttle 和 Sample 操做符與 Where 基本差很少，惟一的區別是:

Throttle 、 Sample 根據時間段過濾
而 Where 根據事件的數據過濾

在抑制快速涌來的輸入流時，這三種操做符提供了三種不一樣的方法。

5. 超時

Timeout 操做符在輸入流上創建一個可調節的超時窗口。一旦新的事件到達，就重置超時窗口。若是超過時限後事件仍沒到達， Timeout 操做符就結束流，併產生一個包含TimeoutException 的 OnError 通知。

public static void TimeoutRun()
{
    IDisposable ob = null;
    var task = Task.Run(() =>
    {
        Thread.Sleep(200);
        //不觸發
        MouseMoveProcess((1, 1));
        MouseMoveProcess((1, 11));
        MouseMoveProcess((1, 111));
        MouseMoveProcess((1, 1111));
        //觸發
        MouseMoveProcess((2, 2), 1100);
        //超時結束
        MouseMoveProcess((2, 22));
        ob?.Dispose();
    });
    ob = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>(
        handler => (s, a) => handler(s, a),
        handler => MouseMove += handler,
        handler => MouseMove -= handler)
    .Select(x => x.EventArgs.GetPosition())
    .Timeout(TimeSpan.FromSeconds(1))//Subscribe後相對一秒超時（連續觸發則不會超時）
    .Subscribe(
        x => Console.WriteLine($"{DateTime.Now.Millisecond}: Saw {x.Item1},{x.Item2}"),
        ex => Console.WriteLine($"{DateTime.Now.Millisecond}: {ex.GetType().Name}"),
        // onCompleted 不會執行
        () => System.Console.WriteLine($"{DateTime.Now.Millisecond}: Finished.")
    );

    System.Console.WriteLine($"{DateTime.Now.Millisecond} Subscribe Done");

    task.Wait();
}

輸出:

138 Subscribe Done
Mouse Move 1,1,After sleep 200.
313: Saw 1,1
Mouse Move 1,11,After sleep 200.
517: Saw 1,11
Mouse Move 1,111,After sleep 200.
722: Saw 1,111
Mouse Move 1,1111,After sleep 200.
923: Saw 1,1111
Mouse Move 2,2,After sleep 1100.
124: Saw 2,2
139: TimeoutException
Mouse Move 2,22,After sleep 200.

在超時以前觀察鼠標移動，超時發生後進行切換

public static event MouseEventHandler OtherMouseMove;

public static void TimeoutMoveRun()
{
    IDisposable ob = null;
    var task = Task.Run(() =>
    {
        Thread.Sleep(200);
        //不觸發
        MouseMoveProcess((1, 1), 400);
        MouseMoveProcess((1, 11), 0);
        //爲了觸發超時
        Thread.Sleep(1100);
        System.Console.WriteLine("sleep: 1100");
        //因爲超時，時間流被遷移到other，下面不會觸發
        MouseMoveProcess((2, 2), 400);
        MouseMoveProcess((2, 22), 400);
        //other的事件,能夠觸發
        OtherMouseMoveProcess((3, 3), 400);
        OtherMouseMoveProcess((3, 33), 400);

        ob?.Dispose();
    });

    var other = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>(
        handler => (s, a) => handler(s, a),
        handler => OtherMouseMove += handler,
        handler => OtherMouseMove -= handler)
    .Select(x => x.EventArgs.GetPosition());

    ob = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>(
        handler => (s, a) => handler(s, a),
        handler => MouseMove += handler,
        handler => MouseMove -= handler)
    .Select(x => x.EventArgs.GetPosition())
    .Timeout(TimeSpan.FromSeconds(1), other)
    .Subscribe(
        x => Console.WriteLine($"{DateTime.Now.Millisecond}: Saw {x.Item1},{x.Item2}"),
        ex => Console.WriteLine($"{DateTime.Now.Millisecond}: {ex.GetType().Name}"));

    System.Console.WriteLine($"{DateTime.Now.Millisecond} Subscribe Done");

    task.Wait();
}

private static void OtherMouseMoveProcess((int, int) xy, int sleepMillsecond = 200)
{
    System.Console.WriteLine($"Other Mouse Move {xy.Item1},{xy.Item2},After sleep {sleepMillsecond}.");
    OtherMouseMove?.Invoke(new object(), new MouseEventArgs(xy));
    Thread.Sleep(sleepMillsecond);
}

輸出:

793 Subscribe Done
Mouse Move 1,1,After sleep 400.
970: Saw 1,1
Mouse Move 1,11,After sleep 0.
373: Saw 1,11
sleep: 1100
Mouse Move 2,2,After sleep 400.
Mouse Move 2,22,After sleep 400.
Other Mouse Move 3,3,After sleep 400.
281: Saw 3,3
Other Mouse Move 3,33,After sleep 400.
684: Saw 3,33

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