C# 非同步程式設計基礎（一·完）：四種非同步呼叫模式完整實戰

測試用非同步元件

public class AsyncDemo {
    private delegate string RunDelegate();
    private string _name; private RunDelegate _del;
    public AsyncDemo(string name) { _name = name; _del = Run; }
    public string Run() => "My name is " + _name;
    public IAsyncResult BeginRun(AsyncCallback cb, object state) => _del.BeginInvoke(cb, state);
    public string EndRun(IAsyncResult ar) => _del.EndInvoke(ar);
}

模式 1：Begin → 執行其他工作 → End (阻塞等待完成)

var demo = new AsyncDemo("jiangnii");
IAsyncResult ar = demo.BeginRun(null, null);
// 做其他事...
string result = demo.EndRun(ar); // 這裡阻塞直到完成
Console.WriteLine(result);

模式 2：輪詢 IsCompleted

while (!ar.IsCompleted) { Console.Write("."); /* 做其他事 */ }
string result = demo.EndRun(ar); // 立即返回

模式 3：AsyncWaitHandle 等待 (可設定逾時)

ar.AsyncWaitHandle.WaitOne(1000, false); // 最多等 1 秒
if (ar.IsCompleted) Console.WriteLine(demo.EndRun(ar));
else Console.WriteLine("逾時未完成");

模式 4：回調函數 + 狀態物件 (最彈性)

static AsyncDemo demo = new AsyncDemo("jiangnii");
static void Main() {
    bool state = false;
    demo.BeginRun(Callback, state);
    Thread.Sleep(1000); // 等待回調完成 (實際應用用 ManualResetEvent 等)
}
static void Callback(IAsyncResult ar) {
    bool state = (bool)ar.AsyncState;
    string result = demo.EndRun(ar);
    Console.WriteLine(state ? result : result + ", isn't it?");
}

委派通用非同步化

任何同步方法皆可透過委派 BeginInvoke/EndInvoke 非同步化，無需類別自行實作 BeginXxx/EndXxx。