任务的返回类型出了错 - 英寸×有错误的返回类型＆QUOT; [英] Task return types gone wrong - "x has the wrong return type"

问题描述

我有一个线code，即：

I have a line of code, that:

bool stop = await Task<bool>.Factory.StartNew(Listen, (TcpClient) client);

和相应的任务：

public static async Task<bool> Listen(object state)
{
    TcpClient client = (TcpClient) state;
    NetworkStream connectionStream = client.GetStream();

    IPEndPoint endPoint = client.Client.RemoteEndPoint as IPEndPoint;

    byte[] buffer = new byte[4096];

    Encoding encoding = Encoding.UTF8;

    Random randomizer = null;

    // Are we still listening?
    bool listening = true;

    // Stop the server afterwards?
    bool stop = false;

    while (listening)
    {
        int bytesRead = await connectionStream.ReadAsync(buffer, 0, buffer.Length);

        if (bytesRead > 0)
        {
            // Create a new byte array for recieved data and populate
            // with data from buffer.
            byte[] messageBytes = new byte[bytesRead];
            Array.Copy(buffer, messageBytes, messageBytes.Length);

            // Generate a message from message bytes.
            string message = encoding.GetString(messageBytes);

            switch (message)
            {
                /*
                Message handling, where one can set stop to true.
                */
            }
        }

        if (bytesRead == 0 || listening == false)
        {   
            client.Client.Dispose();
            break;
        }
    }

    return stop;
}

我已经离开主要部分了code，因为我觉得他们不影响问题的性质。

I have left major parts out of the code, as I feel they do not affect the nature of question.

所以，是的，在运行应用程序时，我得到一个错误：

So yes, when running the application, I get an error:

76: <..>\Program.cs(63,63): Error CS0407: 'System.Threading.Tasks.Task<bool> SOQAsyncQuit.MainClass.Listen(object)' has the wrong return type (CS0407) (SOQAsyncQuit)

好吧，我试图等待Task.Factory.StartNew（...），但后来我结束了一个不同的错误：

Well, I have tried to await Task.Factory.StartNew(...), but then I end up with a different error:

76: <..>\Program.cs(35,35): Error CS0121: The call is ambiguous between the following methods or properties: 'System.Threading.Tasks.TaskFactory.StartNew(System.Action<object>, object)' and 'System.Threading.Tasks.TaskFactory.StartNew<System.Threading.Tasks.Task<bool>>(System.Func<object,System.Threading.Tasks.Task<bool>>, object)' (CS0121) (SOQAsyncQuit)  
76: <..>\Program.cs(57,57): Error CS0407: 'System.Threading.Tasks.Task<bool> SOQAsyncQuit.MainClass.Listen(object)' has the wrong return type (CS0407) (SOQAsyncQuit)
76: <..>\Program.cs(29,29): Error CS0029: Cannot implicitly convert type 'void' to 'bool' (CS0029) (SOQAsyncQuit)

我有工作无效任务，它只是这一点，我很期待转变成一个类型化的结果。因为我是相当新的C＃和.NET总的来说，我在这里的线索。

I have working void tasks, it's just this that I'm looking forward to transform into a typed result. Since I'm fairly new to C# and .NET in general, I'm out of clues here.

我也一直挖通过： http://msdn.microsoft.com /en-us/library/hh524395.aspx ，的 http://msdn.microsoft.com/en-us/library/dd537613（v = vs.110）的.aspx ，SO上的一些问题，不过，他们都没有使用 Task.Factory.StartNew ，我不能设法将它们链接在一起。

I have also been digging through: http://msdn.microsoft.com/en-us/library/hh524395.aspx, http://msdn.microsoft.com/en-us/library/dd537613(v=vs.110).aspx, some questions on SO, though, neither of them use the Task.Factory.StartNew and I cannot manage to link them together.

这里有什么问题？

推荐答案

通常与异步这将是更好地使用 Task.Run 而不是 StartNew 。你不能，如果你打算使用一个状态对象。在这种情况下，你需要修复 StartNew 用法是：

Usually with async it would be better to use Task.Run instead of StartNew. You can't if you plan on using a state object. In this case you need to "fix" the StartNew Usage to be:

bool stop = await Task<Task<bool>>.Factory.StartNew(Listen, client).Unwrap();

收听的返回值是的任务＆LT ;布尔＆GT; ，而不是 BOOL 等 StartNew 的返回类型将需要任务＆LT;任务＆LT;布尔＆GT;＆GT; ，你将需要等待两次或使用展开。 Task.Run 与内置异步记住，所以它做的都是为了你。

Listen's return value is of Task<bool> and not bool, and so StartNew's return type would need to be Task<Task<bool>> which you would need to await twice or use Unwrap. Task.Run was built with async in mind and so it does that all for you.

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