C# 从线程返回值？

如何从线程返回值？

我将使用这种方法并在e.result中返回结果

编辑：

这通常与WinForms和WPF关联，但可由任何类型的.NET应用程序使用。以下是使用BackgroundWorker的控制台应用程序的示例代码：

using System;
using System.Threading;
using System.ComponentModel;
using System.Collections.Generic;
using System.Text;

namespace BGWorker
{
    class Program
    {
        static bool done = false;

        static void Main(string[] args)
        {
            BackgroundWorker bg = new BackgroundWorker();
            bg.DoWork += new DoWorkEventHandler(bg_DoWork);
            bg.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bg_RunWorkerCompleted);
            bg.RunWorkerAsync();

            while (!done)
            {
                Console.WriteLine("Waiting in Main, tid " + Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(100);
            }
        }

        static void bg_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            Console.WriteLine("Completed, tid " + Thread.CurrentThread.ManagedThreadId);
            done = true;
        }

        static void bg_DoWork(object sender, DoWorkEventArgs e)
        {
            for (int i = 1; i <= 5; i++)
            {
                Console.WriteLine("Work Line: " + i + ", tid " + Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(500);
            }
        }
    }
}

2014年更新

见下文@Roger的答案

他指出，您可以使用返回

任务的任务，并选中
任务。C#中用于启动线程的ThreadStart委托的返回类型为“void”

如果希望从线程获取“返回值”，则应在线程完成执行后将其写入共享位置（以适当的线程安全方式）并从中读取。
线程不是方法-通常不会“返回”值

但是，如果您试图从某些处理的结果中提取值，则有许多选项，其中两个主要选项是：


您可以同步共享数据，并对其进行适当设置
您还可以通过某种形式的回调将数据传回

这实际上取决于您如何创建线程，以及您希望如何使用它，以及您正在使用的语言/框架/工具。
线程实际上没有返回值。但是，如果创建委托，可以通过
BeginInvoke
方法异步调用它。这将在线程池线程上执行该方法。您可以通过
EndInvoke
从调用中获取任何返回值

例如：

static int GetAnswer() {
   return 42;
}

...

Func<int> method = GetAnswer;
var res = method.BeginInvoke(null, null); // provide args as needed
var answer = method.EndInvoke(res);

static int GetAnswer（）{
返回42；
}
...
Func方法=获取答案；
var res=method.BeginInvoke（null，null）；//根据需要提供args
var answer=method.EndInvoke（res）；

GetAnswer
将在线程池线程上执行，完成后，您可以通过
EndInvoke
检索答案，如图所示
 下面是一个使用委托的简单示例

void Main()
{
   DoIt d1 = Doer.DoThatThang;
   DoIt d2 = Doer.DoThatThang;

   IAsyncResult r1 = d1.BeginInvoke( 5, null, null );
   IAsyncResult r2 = d2.BeginInvoke( 10, null, null );

   Thread.Sleep( 1000 );

   var s1 = d1.EndInvoke( r1 );
   var s2 = d2.EndInvoke( r2 );

   s1.Dump(); // You told me 5
   s2.Dump(); // You told me 10
}

public delegate string DoIt( int x );

public class Doer
{
  public static string DoThatThang( int x  )
  {
    return "You told me " + x.ToString();
  }
}

在上有一个关于线程的精彩系列。
如果您不想使用BackgroundWorker，而只想使用常规线程，那么您可以触发一个事件来返回如下数据：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;

namespace ThreadWithDataReturnExample
{
    public partial class Form1 : Form
    {
        private Thread thread1 = null;

        public Form1()
        {
            InitializeComponent();

            thread1 = new Thread(new ThreadStart(this.threadEntryPoint));
            Thread1Completed += new AsyncCompletedEventHandler(thread1_Thread1Completed);
        }

        private void startButton_Click(object sender, EventArgs e)
        {
            thread1.Start();
            //Alternatively, you could pass some object
            //in such as Start(someObject);
            //With apprioriate locking, or protocol where
            //no other threads access the object until
            //an event signals when the thread is complete,
            //any other class with a reference to the object 
            //would be able to access that data.
            //But instead, I'm going to use AsyncCompletedEventArgs 
            //in an event that signals completion
        }

        void thread1_Thread1Completed(object sender, AsyncCompletedEventArgs e)
        {
            if (this.InvokeRequired)
            {//marshal the call if we are not on the GUI thread                
                BeginInvoke(new AsyncCompletedEventHandler(thread1_Thread1Completed),
                  new object[] { sender, e });
            }
            else
            {
                //display error if error occurred
                //if no error occurred, process data
                if (e.Error == null)
                {//then success

                    MessageBox.Show("Worker thread completed successfully");
                    DataYouWantToReturn someData = e.UserState as DataYouWantToReturn;
                    MessageBox.Show("Your data my lord: " + someData.someProperty);

                }
                else//error
                {
                    MessageBox.Show("The following error occurred:" + Environment.NewLine + e.Error.ToString());
                }
            }
        }

        #region I would actually move all of this into it's own class
            private void threadEntryPoint()
            {
                //do a bunch of stuff

                //when you are done:
                //initialize object with data that you want to return
                DataYouWantToReturn dataYouWantToReturn = new DataYouWantToReturn();
                dataYouWantToReturn.someProperty = "more data";

                //signal completion by firing an event
                OnThread1Completed(new AsyncCompletedEventArgs(null, false, dataYouWantToReturn));
            }

            /// <summary>
            /// Occurs when processing has finished or an error occurred.
            /// </summary>
            public event AsyncCompletedEventHandler Thread1Completed;
            protected virtual void OnThread1Completed(AsyncCompletedEventArgs e)
            {
                //copy locally
                AsyncCompletedEventHandler handler = Thread1Completed;
                if (handler != null)
                {
                    handler(this, e);
                }
            }
        #endregion

    }
}

使用系统；
使用System.Collections.Generic；
使用系统组件模型；
使用系统数据；
使用系统图；
使用系统文本；
使用System.Windows.Forms；
使用系统线程；
命名空间ThreadWithDataReturnExample
{
公共部分类Form1:Form
{
私有线程thread1=null；
公共表格1（）
{
初始化组件（）；
thread1=新线程（新的ThreadStart（this.threadEntryPoint））；
Thread1Completed+=新的AsyncCompletedEventHandler（thread1\u Thread1Completed）；
}
私有无效开始按钮单击（对象发送者，事件参数e）
{
thread1.Start（）；
//或者，您可以传递一些对象
//例如启动（someObject）；
//具有适当的锁定，或协议，其中
//在之前，没有其他线程访问该对象
//线程完成时发出事件信号，
//引用该对象的任何其他类
//将能够访问该数据。
//但是，我将使用AsyncCompletedEventArgs
//在标志着完成的事件中
}
void thread1\u thread1已完成（对象发送方，AsyncCompletedEventArgs e）
{
if（this.invokererequired）
{//如果我们不在GUI线程上，请封送调用
BeginInvoke（新的AsyncCompletedEventHandler（线程1\u线程1已完成），
新对象[]{sender，e}）；
}
其他的
{
//如果发生错误，则显示错误
//如果没有发生错误，则处理数据
如果（e.Error==null）
{//那就成功了
Show（“工作线程成功完成”）；
DataYouWantToReturn someData=e.UserState为DataYouWantToReturn；
MessageBox.Show（“您的数据，大人：+someData.someProperty”）；
}
else//错误
{
Show（“发生以下错误：”+Environment.NewLine+e.error.ToString（））；
}
}
}
#实际上，我会将所有这些移到它自己的类中
私有void线程入口点（）
{
//做一堆事情
//完成后：
//使用要返回的数据初始化对象
DataYouWantReturn DataYouWantReturn=新数据YouWantReturn（）；
dataYouWantToReturn.someProperty=“更多数据”；
//通过触发事件来发出完成信号
OnThread1Completed（新的AsyncCompletedEventArgs（null、false、DataYouWantReturn））；
}
/// 
///在处理完成或发生错误时发生。
/// 
公共事件AsyncCompletedEventHandler线程1已完成；
Read1已完成时受保护的虚拟无效（AsyncCompletedEventArgs e）
{
//本地复制
AsyncCompletedEventHandler=Thread1Completed；
if（处理程序！=null）
{
处理者（本，e）；
}
}
#端区
}
}
我最喜欢的类，在另一个线程上运行任何方法，只需2行代码

class ThreadedExecuter<T> where T : class
{
    public delegate void CallBackDelegate(T returnValue);
    public delegate T MethodDelegate();
    private CallBackDelegate callback;
    private MethodDelegate method;

    private Thread t;

    public ThreadedExecuter(MethodDelegate method, CallBackDelegate callback)
    {
        this.method = method;
        this.callback = callback;
        t = new Thread(this.Process);
    }
    public void Start()
    {
        t.Start();
    }
    public void Abort()
    {
        t.Abort();
        callback(null); //can be left out depending on your needs
    }
    private void Process()
    {
        T stuffReturned = method();
        callback(stuffReturned);
    }
}

class线程执行器，其中T:class
{
公共委托void CallBackDelegate（T returnValue）；
公共委托T MethodDelegate（）；
私有回调委托回调；
私有方法委托方法；
私有线程t；
公共线程执行器（MethodDelegate方法，CallBackDelegate回调）
{
这个方法=方法；
this.callback=回调；
class ThreadedExecuter<T> where T : class
{
    public delegate void CallBackDelegate(T returnValue);
    public delegate T MethodDelegate();
    private CallBackDelegate callback;
    private MethodDelegate method;

    private Thread t;

    public ThreadedExecuter(MethodDelegate method, CallBackDelegate callback)
    {
        this.method = method;
        this.callback = callback;
        t = new Thread(this.Process);
    }
    public void Start()
    {
        t.Start();
    }
    public void Abort()
    {
        t.Abort();
        callback(null); //can be left out depending on your needs
    }
    private void Process()
    {
        T stuffReturned = method();
        callback(stuffReturned);
    }
}

    void startthework()
    {
        ThreadedExecuter<string> executer = new ThreadedExecuter<string>(someLongFunction, longFunctionComplete);
        executer.Start();
    }
    string someLongFunction()
    {
        while(!workComplete)
            WorkWork();
        return resultOfWork;
    }
    void longFunctionComplete(string s)
    {
        PrintWorkComplete(s);
    }

public class ThreadedMethod<T>
{

    private T mResult;
    public T Result 
    {
        get { return mResult; }
        private set { mResult = value; }
    }

    public ThreadedMethod()
    {
    }

    //If supporting .net 3.5
    public void ExecuteMethod(Func<T> func)
    {
        Result = func.Invoke();
    }

    //If supporting only 2.0 use this and 
    //comment out the other overload
    public void ExecuteMethod(Delegate d)
    {
        Result = (T)d.DynamicInvoke();
    }
}

ThreadedMethod<bool> threadedMethod = new ThreadedMethod<bool>();
Thread workerThread = new Thread((unused) => 
                            threadedMethod.ExecuteMethod(() => 
                                SomeMethod()));
workerThread.Start();
workerThread.Join();
if (threadedMethod.Result == false) 
{
    //do something about it...
}

Public Class ThreadedMethod(Of T)

    Private mResult As T
    Public Property Result() As T
        Get
            Return mResult
        End Get
        Private Set(ByVal value As T)
            mResult = value
        End Set
    End Property

    Sub New()
    End Sub

    'If supporting .net 3.5'
    Function ExecuteMethod(ByVal func As Func(Of T)) As T
        Result = func.Invoke()
        Return Result
    End Function

    'If supporting only 2.0 use this and' 
    'comment out the other overload'
    Function ExecuteMethod(ByVal d As [Delegate]) As T
        Result = DirectCast(d.DynamicInvoke(), T)
        Return Result
    End Function

End Class

void Main()
{
  object value = null; // Used to store the return value
  var thread = new Thread(
    () =>
    {
      value = "Hello World"; // Publish the return value
    });
  thread.Start();
  thread.Join();
  Console.WriteLine(value); // Use the return value here
}

class Program
{
    static void Main(string[] args)
    {
        string returnValue = null;
       new Thread(
          () =>
          {
              returnValue =test() ; 
          }).Start();
        Console.WriteLine(returnValue);
        Console.ReadKey();
    }

    public static string test()
    {
        return "Returning From Thread called method";
    }
}

Setting.Default.ValueToBeSaved;
Setting.Default.Save();

  Task<MyClass> task = Task<MyClass>.Factory.StartNew(() =>
  {
      string s = "my message";
      double d = 3.14159;
      return new MyClass { Name = s, Number = d };
  });
  MyClass test = task.Result;

       // create a list of threads
        List<Thread> threads = new List<Thread>();


        //declare the ref params
        bool is1 = false;
        bool is2 = false;

        threads.Add(new Thread(() => myFunction(someVar, ref is1)));
        threads.Add(new Thread(() => myFunction(someVar, ref is2)));

        threads.ForEach(x => x.Start());

        // wait for threads to finish
        threads.ForEach(x => x.Join());

        //check the ref params
        if (!is1)
        {
          //do something
        }

        if (!is2)
        {
           //do somethign else
        }

 bool theirFunction(var someVar){
   return false;
}


 void myFunction(var someVar ref bool result){
  result = theirFunction(myVar);
 }

class Anything {
    // Number and Text are for instructional purposes only
    public int Number { get; set; }
    public string Text { get; set; }
    // Data can be any object - even another class
    public object Data { get; set; }
}

class AnyTask {

    private object m_lock;

    public AnyTask() {
        m_lock = new object();
    }
    // Something to use the delegate
    public event MainDelegate OnUpdate;

    public void Test_Function(int count) {
        var list = new List<Thread>(count);
        for (var i = 0; i < count; i++) {
            var thread = new Thread(new ParameterizedThreadStart(Thread_Task));
            var item = new Anything() {
                Number = i,
                Text = String.Format("Test_Function #{0}", i)
            };
            thread.Start(item);
            list.Add(thread);
        }
        foreach (var thread in list) {
            thread.Join();
        }
    }

    private void MainUpdate(Anything item, bool original) {
        if (OnUpdate != null) {
            OnUpdate(item, original);
        }
    }

    private void Thread_Task(object parameter) {
        lock (m_lock) {
            var item = (Anything)parameter;
            MainUpdate(item, true);
            item.Text = String.Format("{0}; Thread_Task #{1}", item.Text, item.Number);
            item.Number = 0;
            MainUpdate(item, false);
        }
    }

}

// A delegate makes life simpler
delegate void MainDelegate(Anything sender, bool original);

class Program {

    private const int COUNT = 15;
    private static List<Anything> m_list;

    static void Main(string[] args) {
        m_list = new List<Anything>(COUNT);
        var obj = new AnyTask();
        obj.OnUpdate += new MainDelegate(ThreadMessages);
        obj.Test_Function(COUNT);
        Console.WriteLine();
        foreach (var item in m_list) {
            Console.WriteLine("[Complete]:" + item.Text);
        }
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }

    private static void ThreadMessages(Anything item, bool original) {
        if (original) {
            Console.WriteLine("[main method]:" + item.Text);
        } else {
            m_list.Add(item);
        }
    }

}

Imports System.Threading

Delegate Sub MainDelegate(sender As Anything, original As Boolean)

Class Main

    Private Const COUNT As Integer = 15
    Private Shared m_list As List(Of Anything)

    Public Shared Sub Main(args As String())
        m_list = New List(Of Anything)(COUNT)
        Dim obj As New AnyTask()
        AddHandler obj.OnUpdate, New MainDelegate(AddressOf ThreadMessages)
        obj.Test_Function(COUNT)
        Console.WriteLine()
        For Each item As Anything In m_list
            Console.WriteLine("[Complete]:" + item.Text)
        Next
        Console.WriteLine("Press any key to exit.")
        Console.ReadKey()
    End Sub

    Private Shared Sub ThreadMessages(item As Anything, original As Boolean)
        If original Then
            Console.WriteLine("[main method]:" + item.Text)
        Else
            m_list.Add(item)
        End If
    End Sub

End Class

Class AnyTask

    Private m_lock As Object

    Public Sub New()
        m_lock = New Object()
    End Sub
    ' Something to use the delegate
    Public Event OnUpdate As MainDelegate

    Public Sub Test_Function(count As Integer)
        Dim list As New List(Of Thread)(count)
        For i As Int32 = 0 To count - 1
            Dim thread As New Thread(New ParameterizedThreadStart(AddressOf Thread_Task))
            Dim item As New Anything()
            item.Number = i
            item.Text = String.Format("Test_Function #{0}", i)
            thread.Start(item)
            list.Add(thread)
        Next
        For Each thread As Thread In list
            thread.Join()
        Next
    End Sub

    Private Sub MainUpdate(item As Anything, original As Boolean)
        RaiseEvent OnUpdate(item, original)
    End Sub

    Private Sub Thread_Task(parameter As Object)
        SyncLock m_lock
            Dim item As Anything = DirectCast(parameter, Anything)
            MainUpdate(item, True)
            item.Text = [String].Format("{0}; Thread_Task #{1}", item.Text, item.Number)
            item.Number = 0
            MainUpdate(item, False)
        End SyncLock
    End Sub

End Class


Class Anything
    ' Number and Text are for instructional purposes only
    Public Property Number() As Integer
        Get
            Return m_Number
        End Get
        Set(value As Integer)
            m_Number = value
        End Set
    End Property
    Private m_Number As Integer
    Public Property Text() As String
        Get
            Return m_Text
        End Get
        Set(value As String)
            m_Text = value
        End Set
    End Property
    Private m_Text As String
    ' Data can be anything or another class
    Public Property Data() As Object
        Get
            Return m_Data
        End Get
        Set(value As Object)
            m_Data = value
        End Set
    End Property
    Private m_Data As Object
End Class

object result = null;
Thread thread = new System.Threading.Thread(() => { 
    //Some work...
    result = 42; });
thread.Start();
thread.Join();
Console.WriteLine(result);

delegate object MyFunc();
...
MyFunc x = new MyFunc(() => { 
    //Some work...
    return 42; });
IAsyncResult asyncResult = x.BeginInvoke(null, null);
object result = x.EndInvoke(asyncResult);

BackgroundWorker worker = new BackgroundWorker();
worker.DoWork += (s, e) => {
    //Some work...
    e.Result = 42;
};
worker.RunWorkerCompleted += (s, e) => {
    //e.Result "returned" from thread
    Console.WriteLine(e.Result);
};
worker.RunWorkerAsync();

//Main thread will be blocked until task thread finishes
//(because of obtaining the value of the Result property)
int result = Task.Factory.StartNew(() => {
    //Some work...
    return 42;}).Result;

int result = await Task.Run(() => {
    //Some work...
    return 42; });

int val;
Thread thread = new Thread(() => { val = Multiply(1, 2); });
thread.Start();

int Multiply(int x, int y)
{
    return x * y;
}

 private Object MyThread(Object Data)
      {
        Object response = null;
        Thread newThread = new Thread(() =>
        {
            response = MyFunction(Data);
            //MyFunction Is Function that you Define
        });
        newThread.Start();
        newThread.Join();
        return response;
      }

class Program
{
    public static void ActionResultPrint(string i)
    {
        Console.WriteLine(i);
    }

    static void Main(string[] args)
    {
        var tl = new List<Thread>();

        tl.Add(new Thread(() => Run(10, ActionResultPrint)));
        tl.Add(new Thread(() => Run(20, ActionResultPrint)));
        tl.ForEach(x => x.Start());
        tl.ForEach(x => x.Join());
    }

    public static void Run(int j, Action<string> action)
    {
        string rvalue = string.Empty;

        for (int i = 0; i <= j; i++)
        {
            Thread.Sleep(100);
            rvalue = i.ToString();
            Console.WriteLine(rvalue);
        }
        action($@"output {j}");
    }
}