從子線程傳回值

使用回調方法檢索資料

下面的樣本示範了一個從線程中檢索資料的回調方法。包含資料和線程方法的類的建構函式也接受代表回調方法的委託；線上程方法結束前，它調用該回調委託。

 

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);
    }
}