winform程序异步调用(IAsyncResult 接口和AsyncCallback 委托)

微软IAsyncResult 接口接口实现异步调用
微软官方文档：
IAsyncResult 接口：https://docs.microsoft.com/zh-cn/dotnet/api/system.iasyncresult?redirectedfrom=MSDN&view=net-6.0
AsyncCallback 委托：https://docs.microsoft.com/zh-cn/dotnet/api/system.asynccallback?view=net-6.0

IAsyncResult 接口在使用委托异步调用方法时返回 AsyncResult ，IAsyncResult； 异步调用由 BeginInvoke 的实现。
首先定义一个委托

//定义一个委托
 public delegate string AsyncMethodCaller(int callDuration);
 public void DoAsyncMethod()
 {
     TestAsync.AsyncMethodCaller asyncMethodCaller = new TestAsync.AsyncMethodCaller(TestMethod);
     //BeginInvoke实现异步调用
     IAsyncResult result = asyncMethodCaller.BeginInvoke(100, null, null);
     result.AsyncWaitHandle.WaitOne(100);
     // 获取结果
     string returnValue = asyncMethodCaller.EndInvoke(result);
     //if (result.IsCompleted)也可以先判断线程是否调用结束
         // 关闭等待的线程
         //result.AsyncWaitHandle.Close();
     // 关闭等待的线程
     result.AsyncWaitHandle.Close();
 }
       
 public string TestMethod(int callDuration)
 {
     Thread.Sleep(callDuration);
     int threadId = Thread.CurrentThread.ManagedThreadId;
     return String.Format("The call ManagedThreadId was {0}.", threadId.ToString());
 }