C# 多线程返回值

ThreadStart 委托既没有参数也没有返回值。这意味着不可以使用需要参数的方法启动线程，或从方法中获得返回值。

为向线程传递数据，需要创建一个用来保持数据和线程方法的对象，如下面的两个代码示例所示。
为检索线程方法的结果，您可以使用回调方法，如第二个代码示例中所示。
using System;
using System.Threading;

// The ThreadWithState class contains the information needed for
// a task, and the method that executes the task.
//
public class ThreadWithState {
// State information used in the task.
private string boilerplate;
private int value;

// The constructor obtains the state information.
public ThreadWithState(string text, int number) {
boilerplate = text;
value = number;
}

// The thread procedure performs the task, such as formatting
// and printing a document.
public void ThreadProc() {
Console.WriteLine(boilerplate, value);
}
}

// Entry point for the example.
//
public class Example {
public static void Main() {
// Supply the state information required by the task.
ThreadWithState tws =
new ThreadWithState("This report displays the number {0}.", 42);
// Create a thread to execute the task, and then
// start the thread.
Thread t = new Thread(new ThreadStart(tws.ThreadProc));
t.Start();
Console.WriteLine("Main thread does some work, then waits.");
t.Join();
Console.WriteLine("Independent task has completed; main thread ends.");
}
}
用回调方法检索数据
下面的示例演示了一个从线程中检索数据的回调方法。包含数据和线程方法的类的构造函数也接受代表回调方法的委托；在线程方法结束前，它调用该回调委托。
using System;
using System.Threading;

// The ThreadWithState class contains the information needed for
// a task, the method that executes the task, and a delegate
// to call when the task is complete.
//
public class ThreadWithState {
// State information used in the task.
private string boilerplate;
private int value;
// Delegate used to execute the callback method when the
// task is complete.
private ExampleCallback callback;

// The constructor obtains the state information and the
// callback delegate.
public ThreadWithState(string text, int number,
ExampleCallback callbackDelegate)
{
boilerplate = text;
value = number;
callback = callbackDelegate;
}

// The thread procedure performs the task, such as
// formatting and printing a document, and then invokes
// the callback delegate with the number of lines printed.
public void ThreadProc() {
Console.WriteLine(boilerplate, value);
if (callback != null)
callback(1);
}
}

// Delegate that defines the signature for the callback method.
//
public delegate void ExampleCallback(int lineCount);

// Entry point for the example.
//
public class Example {
public static void Main() {
// Supply the state information required by the task.
ThreadWithState tws = new ThreadWithState(
"This report displays the number {0}.",
42,
new ExampleCallback(ResultCallback)
);

Thread t = new Thread(new ThreadStart(tws.ThreadProc));
t.Start();
Console.WriteLine("Main thread does some work, then waits.");
t.Join();
Console.WriteLine("Independent task has completed; main thread ends.");
}

// The callback method must match the signature of the
// callback delegate.
//
public static void ResultCallback(int lineCount) {
Console.WriteLine("Independent task printed {0} lines.", lineCount);
}
}