我有这个返回的方法string:
public string SendResponse(HttpListenerRequest request)
{
string result = "";
string key = request.QueryString.GetKey(0);
if (key == "cmd")
{
if (request.QueryString[0] == "uploadstatus")
{
switch (Youtube_Uploader.uploadstatus)
{
case "uploading file":
return "uploading " + Youtube_Uploader.fileuploadpercentages;
case "status":
return Youtube_Uploader.fileuploadpercentages.ToString();
case "file uploaded successfully":
Youtube_Uploader.uploadstatus = "";
return "upload completed," + Youtube_Uploader.fileuploadpercentages + ","
+ Youtube_Uploader.time;
default:
return "upload unknown state";
}
}
if (request.QueryString[0] == "nothing")
{
return "Connection Success";
}
if (request.QueryString[0] == "start")
{
StartRecrod();
result = "Recording started";
}
if (request.QueryString[0] == "stop")
{
dirchanged = false;
StartRecrod();
result = "Recording stopped and preparing the file to be shared on youtube";
string fileforupload = await WatchDirectory();
await WaitForUnlockedFile(fileforupload);
using (StreamWriter w = new StreamWriter(userVideosDirectory + "\\UploadedVideoFiles.txt", true))
{
w.WriteLine(fileforupload);
}
uploadedFilesList.Add(fileforupload);
Youtube_Uploader youtubeupload = new Youtube_Uploader(uploadedFilesList[0]);
}
}
else
{
result = "Nothing have been done";
}
return result;
}
问题是在这个方法中我使用了两行await:
string fileforupload = await WatchDirectory();
await WaitForUnlockedFile(fileforupload);
并在这两行上出现错误。这两个错误是相同的：
错误“await”运算符只能在异步方法中使用。
考虑使用“async”修饰符标记此方法并更改
它的返回类型为'Task<string>'.
问题是否有可能使SendResponse()方法返回字符串，因为我需要它并且还使用await?
这就是我需要使用的两种方法await in the SendResponse() method:
private async Task<string> WatchDirectory()
{
using (FileSystemWatcher watcher = new FileSystemWatcher())
{
TaskCompletionSource<string> tcs = new TaskCompletionSource<string>();
watcher.Path = userVideosDirectory;
watcher.NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.Size;
watcher.Filter = "*.mp4";
watcher.Changed += (sender, e) => tcs.SetResult(e.FullPath);
watcher.EnableRaisingEvents = true;
return await tcs.Task;
}
}
// You can get rid of the OnChanged() method altogether
private async Task WaitForUnlockedFile(string fileName)
{
while (true)
{
try
{
using (IDisposable stream = File.Open(fileName, FileMode.OpenOrCreate,
FileAccess.ReadWrite, FileShare.None))
{ /* on success, immediately dispose object */ }
break;
}
catch (IOException)
{
// ignore exception
// NOTE: for best results, consider checking the hresult value of
// the exception, to ensure that you are only ignoring the access violation
// exception you're expecting, rather than other exceptions, like
// FileNotFoundException, etc. which could result in a hung process
}
// You might want to consider a longer delay...maybe on the order of
// a second or two at least.
await Task.Delay(100);
}
}
UPDATE:
我改变了方法SendResponse() to be async Task<string>但随后在WebServer类构造函数我有这个并在这一行出现错误：
WebServer ws = new WebServer(SendResponseAsync, "http://+:8098/");
（SendResponseAsync是SendResponse改名了）
错误是：
错误 1“System.Threading.Tasks.Task Automatic_Record.Form1.SendResponseAync(System.Net.HttpListenerRequest)”返回类型错误
WebServer 类是：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Threading;
namespace Automatic_Record
{
class WebServer
{
private readonly HttpListener _listener = new HttpListener();
private readonly Func<HttpListenerRequest, string> _responderMethod;
public WebServer(string[] prefixes, Func<HttpListenerRequest, string> method)
{
if (!HttpListener.IsSupported)
throw new NotSupportedException(
"Needs Windows XP SP2, Server 2003 or later.");
// URI prefixes are required, for example
// "http://localhost:8080/index/".
if (prefixes == null || prefixes.Length == 0)
throw new ArgumentException("prefixes");
// A responder method is required
if (method == null)
throw new ArgumentException("method");
foreach (string s in prefixes)
_listener.Prefixes.Add(s);
_responderMethod = method;
_listener.Start();
}
public WebServer(Func<HttpListenerRequest, string> method, params string[] prefixes)
: this(prefixes, method) { }
public void Run()
{
ThreadPool.QueueUserWorkItem((o) =>
{
Console.WriteLine("Webserver running...");
try
{
while (_listener.IsListening)
{
ThreadPool.QueueUserWorkItem((c) =>
{
var ctx = c as HttpListenerContext;
try
{
string rstr = _responderMethod(ctx.Request);
System.Diagnostics.Trace.Write(ctx.Request.QueryString);
//ctx.Request.QueryString
byte[] buf = Encoding.UTF8.GetBytes(rstr);
ctx.Response.ContentLength64 = buf.Length;
ctx.Response.OutputStream.Write(buf, 0, buf.Length);
System.Data.SqlClient.SqlConnectionStringBuilder builder = new System.Data.SqlClient.SqlConnectionStringBuilder();
}
catch { } // suppress any exceptions
finally
{
// always close the stream
ctx.Response.OutputStream.Close();
}
}, _listener.GetContext());
}
}
catch { } // suppress any exceptions
});
}
public void Stop()
{
_listener.Stop();
_listener.Close();
}
}
}
UPDATE 2
我尝试了 Peter 解决方案，所以我将 WebServer 类代码更改为 Peter 在这个问题解决方案中显示的代码。
然后在 form1 构造函数中我做了：
var ws = new WebServer(
() => Task.Run(request => SendResponseAsync(request)),
"http://+:8098/");
ws.Run();
然后是SendResponseAsync方法：
public async Task<string> SendResponseAsync(HttpListenerRequest request)
{
string result = "";
string key = request.QueryString.GetKey(0);
if (key == "cmd")
{
if (request.QueryString[0] == "uploadstatus")
{
switch (Youtube_Uploader.uploadstatus)
{
case "uploading file":
return "uploading " + Youtube_Uploader.fileuploadpercentages;
case "status":
return Youtube_Uploader.fileuploadpercentages.ToString();
case "file uploaded successfully":
Youtube_Uploader.uploadstatus = "";
return "upload completed," + Youtube_Uploader.fileuploadpercentages + ","
+ Youtube_Uploader.time;
default:
return "upload unknown state";
}
}
if (request.QueryString[0] == "nothing")
{
return "Connection Success";
}
if (request.QueryString[0] == "start")
{
StartRecrod();
result = "Recording started";
}
if (request.QueryString[0] == "stop")
{
dirchanged = false;
StartRecrod();
result = "Recording stopped and preparing the file to be shared on youtube";
string fileforupload = await WatchDirectory();
await WaitForUnlockedFile(fileforupload);
using (StreamWriter w = new StreamWriter(userVideosDirectory + "\\UploadedVideoFiles.txt", true))
{
w.WriteLine(fileforupload);
}
uploadedFilesList.Add(fileforupload);
Youtube_Uploader youtubeupload = new Youtube_Uploader(uploadedFilesList[0]);
}
}
else
{
result = "Nothing have been done";
}
return result;
}
手表目录：
private async Task<string> WatchDirectory()
{
using (FileSystemWatcher watcher = new FileSystemWatcher())
{
TaskCompletionSource<string> tcs = new TaskCompletionSource<string>();
watcher.Path = userVideosDirectory;
watcher.NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.Size;
watcher.Filter = "*.mp4";
watcher.Changed += (sender, e) => tcs.SetResult(e.FullPath);
watcher.EnableRaisingEvents = true;
return await tcs.Task;
}
}
最后是 WaitForUnlockedFile
private async Task WaitForUnlockedFile(string fileName)
{
while (true)
{
try
{
using (IDisposable stream = File.Open(fileName, FileMode.OpenOrCreate,
FileAccess.ReadWrite, FileShare.None))
{ /* on success, immediately dispose object */ }
break;
}
catch (IOException)
{
// ignore exception
// NOTE: for best results, consider checking the hresult value of
// the exception, to ensure that you are only ignoring the access violation
// exception you're expecting, rather than other exceptions, like
// FileNotFoundException, etc. which could result in a hung process
}
// You might want to consider a longer delay...maybe on the order of
// a second or two at least.
await Task.Delay(100);
}
}
但线上出现错误：
任务.运行
严重性代码 说明 项目文件行错误 无法将 lambda 表达式转换为类型“string[]”，因为它不是委托类型 Automatic_Record
并且线上也出现错误“http://+:8098/”
严重性代码说明项目文件行错误参数 2：无法从“string”转换为“System.Func>”
