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c# - 等到甚至发生并在处理后继续

问题描述

我正在远程控制外部摄像头。我可以通过异步调用TakePhotoAsync()方法来拍照，当拍照并准备好下载时，DownloadReady会发生包含关于拍照的DownloadInfo的事件。我有方法Cam_DownloadReady(...)来处理这个事件。这是由 API 提供的，我无法更改任何内容。

但我需要同步拍照。类似于 callTakePhotoAsync()并在这一行等待直到事件DownloadReady发生，它调用Cam_DownloadReady(...)方法，然后在执行并完成此方法后，然后// continue..（如代码部分中标记的那样）。这可能吗？谢谢

public Task<CameraImage> GetImageFromCameraAsync(string cameraId) 
{
    APIHandler = new CanonAPI();
    Camera MainCamera = APIHandler.GetCameraList()[0];
    MainCamera.DownloadReady += Cam_DownloadReady;
    MainCamera.OpenSession();
    MainCamera.TakePhotoAsync();
    // wait here until event occurs and is processed
    // Cam_DownloadReady(...) is called and finished
    // continue ...
}

private void Cam_DownloadReady(Camera sender, DownloadInfo Info)
{
    sender.DownloadFile(Info, saveImageDir); //save picture on PC
}

标签： c#asynchronousevents

解决方案

您可以通过使用ManualResetEvent来实现：

using System.Threading;     
public ManualResetEvent mre = new ManualResetEvent(false); // created in the unsignaled state.

    public Task<CameraImage> GetImageFromCameraAsync(string cameraId)
    {
        mre.Reset(); // Set the state of the event to be nonsignaled 
        APIHandler = new CanonAPI();
        Camera MainCamera = APIHandler.GetCameraList()[0];
        MainCamera.DownloadReady += Cam_DownloadReady;
        MainCamera.OpenSession();
        MainCamera.TakePhotoAsync();
        // wait here until event occurs and is processed
        mre.WaitOne(); // Block the current thread until the current wait handle receives a signal
        // Cam_DownloadReady(...) is called and finished
        // continue ...
    }

    private void Cam_DownloadReady(Camera sender, DownloadInfo Info)
    {
        sender.DownloadFile(Info, saveImageDir); //save picture on PC
        mre.Set(); // Set the state of the event to signaled, allowing mre.WaitOne() above to proceed.
    }

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