我正在尝试公开一个ASP.NET Web API,该API必须捕获并返回照片作为附件。 我正在使用CameraControl.Devices 2.1.0-beta来控制尼康DSLR和.NET 4.6。
但是我的行为很不一致。有时第一个HTTP请求设法返回一张照片,但是从那里开始,在组成最终的HttpResponseMessage之前,它就停止了,然后HTTP请求挂起并超时。我相信这是异步操作造成的僵局。它始终执行DeviceManager_PhotoCaptured中的逻辑,该逻辑将照片从DSLR传输到文件夹。有时候,它甚至可以从单个请求中拍摄两张照片。
我在做什么错?您知道更好的方法吗?
using System;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http;
using CameraControl.Devices;
using CameraControl.Devices.Classes;
public class PhotosController : ApiController
{
public string FolderForPhotos = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyPictures), "Test");
private TaskCompletionSource<string> TaskCompletionSource = null;
private CameraDeviceManager DeviceManager = null;
// GET api/photos
public async Task<HttpResponseMessage> Get()
{
TaskCompletionSource = new TaskCompletionSource<string>();
DeviceManager = new CameraDeviceManager();
DeviceManager.StartInNewThread = false;
DeviceManager.PhotoCaptured += DeviceManager_PhotoCaptured;
DeviceManager.ConnectToCamera();
DeviceManager.SelectedCameraDevice.CapturePhoto();
var fileName = await TaskCompletionSource.Task.ConfigureAwait(continueOnCapturedContext: false);
HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
var stream = new FileStream(fileName, FileMode.Open);
result.Content = new StreamContent(stream);
result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
result.Content.Headers.ContentDisposition.FileName = Path.GetFileName(fileName);
result.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpg");
result.Content.Headers.ContentLength = stream.Length;
return result;
}
private void DeviceManager_PhotoCaptured(object sender, PhotoCapturedEventArgs eventArgs)
{
if (eventArgs == null)
{
TaskCompletionSource.TrySetException(new Exception("eventArgs is empty"));
return;
}
try
{
string fileName = Path.Combine(FolderForPhotos, Path.GetFileName(eventArgs.FileName));
// if file exist try to generate a new filename to prevent file lost.
// This useful when camera is set to record in ram the the all file names are same.
if (File.Exists(fileName))
fileName =
StaticHelper.GetUniqueFilename(
Path.GetDirectoryName(fileName) + "\\" + Path.GetFileNameWithoutExtension(fileName) + "_", 0,
Path.GetExtension(fileName));
// check the folder of filename, if not found create it
if (!Directory.Exists(Path.GetDirectoryName(fileName)))
{
Directory.CreateDirectory(Path.GetDirectoryName(fileName));
}
eventArgs.CameraDevice.TransferFile(eventArgs.Handle, fileName);
// the IsBusy may used internally, if file transfer is done should set to false
eventArgs.CameraDevice.IsBusy = false;
TaskCompletionSource.TrySetResult(fileName);
}
catch (Exception exception)
{
TaskCompletionSource.TrySetException(exception);
eventArgs.CameraDevice.IsBusy = false;
}
finally
{
DeviceManager.CloseAll();
}
}
}
答案 0 :(得分:0)
我知道了:
我必须将TaskCompletionSource
设为静态字段。我猜出于某种原因,当它是一个实例字段时,它最终被释放或分离。
private static TaskCompletionSource<string> TaskCompletionSource = null;