c# - 使用RX同步多个事件

Question

假设我的列表中有三种产品。为了启用特定操作，所有三个都必须属于特定类型。为了找出产品的类型，我需要调用服务电话并等待响应。

我想做的是等待所有三个响应(可能会超时，以防出现问题)，并在收集所有信息后，决定是否启用可能的操作。

我曾经通过一些计数器或重置事件来跟踪已完成的事件来解决这个问题，但我想看看是否可以使用 Rx 以更干净的方式来完成它。

由于我对 Rx 还不太熟悉，所以我正在寻找一些提示/指针。我明白我可以使用

Observable.FromEventPattern

对于我正在等待的事件。我订阅并等待响应并处理它。我只是不清楚如何组合多个事件。

Answer 1

您正在寻找的组合器是CombineLatest

假设你有一门这样的类(class):

public class Foo
{
    public delegate void FooEventHandler(object sender, EventArgs args);

    public event FooEventHandler FirstEvent = delegate {};    
    public event FooEventHandler SecondEvent = delegate {};    
    public event FooEventHandler ThirdEvent = delegate {};    

    public void DoIt()
    {
        FireOne();
        FireTwo();
        FireThree();
    }

    public void FireOne()
    {
        Console.WriteLine("Firing event 1...");
        Thread.Sleep(1000);
        FirstEvent(this, new EventArgs());
    }
    public void FireTwo()
    {
        Console.WriteLine("Firing event 2...");
        Thread.Sleep(1000);
        SecondEvent(this, new EventArgs());
    }
    public void FireThree()
    {
        Console.WriteLine("Firing event 3...");
        Thread.Sleep(1000);
        ThirdEvent(this, new EventArgs());
    }
}

首先，您需要将这些事件“转换”为 Observable:

var foo = new Foo();
var firstWatcher = Observable.FromEventPattern(foo, "FirstEvent");
var secondWatcher = Observable.FromEventPattern(foo, "SecondEvent");
var thirdWatcher = Observable.FromEventPattern(foo, "ThirdEvent");

现在您需要“仅在所有这些都已触发时才触发”选择器，即 CombineLatest:

var allDone = Observable.CombineLatest(firstWatcher, secondWatcher, thirdWatcher);

并进行测试:

using(allDone.Subscribe(_ => Console.WriteLine("Boop! You sunk my battleship!")))
{
    foo.DoIt();
}    

替代“测试工具”:

var foo = new Foo();
var firstWatcher = Observable.FromEventPattern(foo, "FirstEvent");
var secondWatcher = Observable.FromEventPattern(foo, "SecondEvent");
var thirdWatcher = Observable.FromEventPattern(foo, "ThirdEvent");

var allDone = Observable.CombineLatest(firstWatcher, secondWatcher, thirdWatcher);

// keep a handle on the subscription            
IDisposable subscription = null;

// to prevent premature exiting...
var blocker = new ManualResetEvent(false);

// explicit subscribe
subscription = allDone.Subscribe(
    whoCares => 
    {
        Console.WriteLine("BOOM! We're done!");
        // always clean up after yourself
        if(subscription != null)
        {
            subscription.Dispose();
        }
        // it's ok, we can quit now
        blocker.Set();
    });

foo.DoIt();

// Wait until it's clear to go ahead...
blocker.WaitOne();