c# - 从遗留类(启动方法 + 事件)创建任务(或可观察对象)

Question

我有一个遗留类，我想以更方便的方式使用它。

class Camera 
{
     void RequestCapture();
     public delegate void ReadResultEventHandler(ControllerProxy sender, ReadResult readResult);
     public event ReadResultEventHandler OnReadResult;
}

类(class)管理一个拍照的相机。它的工作原理是:

1. 调用 RequestCapture 方法
2. 等待引发 OnReadResult(显然，您需要订阅此事件才能获取捕获的数据)

操作是异步的。 RequestCapture 是一种即发即弃操作(快速!)操作。几秒钟后，事件将引发。

我想像平常一样食用它 Task或作为 IObservable<ReadResult>但我很迷茫，因为它不适应异步模式，而且我从未使用过这样的类。

Answer 1

按照 this article 中的示例我的基本方法(未经测试!!)将是:

class AsyncCamera
{
    private readonly Camera camera;
    
    public AsyncCamera(Camera camera)
    {
        this.camera = camera ?? throw new ArgumentNullException(nameof(camera));
    } 

    public Task<ReadResult> CaptureAsync()
    {
         TaskCompletionSource<ReadResult> tcs = new TaskCompletionSource<ReadResult>();
         camera.OnReadResult += (sender, result) => {
             tcs.TrySetResult(result);
         };
         camera.RequestCapture();
         return tcs.Task;
    }
}

可能的用法:

public async Task DoSomethingAsync()
{
    var asyncCam = new AsyncCamera(new Camera());
    var readResult = await asyncCam.CaptureAsync();
    // use readResult
}

---

考虑到 Stephen 的评论进行编辑(感谢您!)

所以，这是我对取消订阅事件处理程序的幼稚看法。我没有时间进行任何测试，因此欢迎提出改进建议。

class AsyncCamera
{
    private readonly Camera camera;
    
    public AsyncCamera(Camera camera)
    {
        this.camera = camera ?? throw new ArgumentNullException(nameof(camera));
    } 

    public Task<ReadResult> CaptureAsync()
    {
         ReadResultEventHandler handler = null;
         TaskCompletionSource<ReadResult> tcs = new TaskCompletionSource<ReadResult>();

         handler = (sender, result) => {
             camera.OnReadResult -= handler;
             tcs.TrySetResult(result);
         };

         camera.OnReadResult += handler;
         camera.RequestCapture();
         return tcs.Task;
    }
}

以防评论被“清理”:斯蒂芬说

Unsubscription isn't handled in the MS examples, but it really should be. You'd have to declare a variable of type ReadResultDelegate (or whatever it's called), set it to null, and then set it to the lambda expression which can then unsubscribe that variable from the event. I don't have an example of this on my blog, but there's a general-purpose one here. Which, now that I look at it, does not seem to handle cancellation appropriately. – Stephen Cleary

我强调的。

似乎有效:https://dotnetfiddle.net/9XsaUB