以結束異步作業的方式封鎖應用程式的執行

在等候異步作的結果時，無法繼續執行其他工作的應用程式必須封鎖，直到作業完成為止。 在等候異步作完成時，請使用下列其中一個選項來封鎖應用程式的主要線程：

• 請呼叫 EndOperationName 方法進行非同步操作。 本主題將示範此方法。

• 使用異步操作的 BeginOperationName 方法所傳回之 IAsyncResult 的 AsyncWaitHandle 屬性。 如需展示此方法的範例，請參閱 使用 AsyncWaitHandle封鎖應用程式執行。

使用 EndOperationName 方法來封鎖的應用程式，直到異步作完成之前，通常會呼叫 BeginOperationName 方法，執行任何不需要作業結果即可完成的工作，然後呼叫 EndOperationName。

範例

下列程式代碼範例示範如何使用 Dns 類別中的異步方法來擷取使用者指定計算機的域名系統資訊。 請注意，null（Visual Basic 中的Nothing）會針對 BeginGetHostByNamerequestCallback 和 stateObject 參數傳遞，因為這些自變數在使用此方法時並非必要。

/*
The following example demonstrates using asynchronous methods to
get Domain Name System information for the specified host computer.
*/

using System;
using System.Net;
using System.Net.Sockets;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class BlockUntilOperationCompletes
    {
        public static void Main(string[] args)
        {
            // Make sure the caller supplied a host name.
            if (args.Length == 0 || args[0].Length == 0)
            {
                // Print a message and exit.
                Console.WriteLine("You must specify the name of a host computer.");
                return;
            }
            // Start the asynchronous request for DNS information.
            // This example does not use a delegate or user-supplied object
            // so the last two arguments are null.
            IAsyncResult result = Dns.BeginGetHostEntry(args[0], null, null);
            Console.WriteLine("Processing your request for information...");
            // Do any additional work that can be done here.
            try
            {
                // EndGetHostEntry blocks until the process completes.
                IPHostEntry host = Dns.EndGetHostEntry(result);
                string[] aliases = host.Aliases;
                IPAddress[] addresses = host.AddressList;
                if (aliases.Length > 0)
                {
                    Console.WriteLine("Aliases");
                    for (int i = 0; i < aliases.Length; i++)
                    {
                        Console.WriteLine($"{aliases[i]}");
                    }
                }
                if (addresses.Length > 0)
                {
                    Console.WriteLine("Addresses");
                    for (int i = 0; i < addresses.Length; i++)
                    {
                        Console.WriteLine($"{addresses[i].ToString()}");
                    }
                }
            }
            catch (SocketException e)
            {
                Console.WriteLine($"An exception occurred while processing the request: {e.Message}");
            }
        }
    }
}

' The following example demonstrates using asynchronous methods to
' get Domain Name System information for the specified host computer.

Imports System.Net
Imports System.Net.Sockets

Namespace Examples.AdvancedProgramming.AsynchronousOperations
    Public Class BlockUntilOperationCompletes
        Public Shared Sub Main(args() as String)
            ' Make sure the caller supplied a host name.
            If (args.Length = 0)
                ' Print a message and exit.
                Console.WriteLine("You must specify the name of a host computer.")
                End
            End If
            ' Start the asynchronous request for DNS information.
            ' This example does not use a delegate or user-supplied object
            ' so the last two arguments are Nothing.
            Dim result as IAsyncResult = Dns.BeginGetHostEntry(args(0), Nothing, Nothing)
            Console.WriteLine("Processing your request for information...")
            ' Do any additional work that can be done here.
            Try
                ' EndGetHostByName blocks until the process completes.
                Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
                Dim aliases() as String = host.Aliases
                Dim addresses() as IPAddress = host.AddressList
                Dim i as Integer
                If aliases.Length > 0
                    Console.WriteLine("Aliases")
                    For i = 0 To aliases.Length - 1
                        Console.WriteLine("{0}", aliases(i))
                    Next i
                End If
                If addresses.Length > 0
                    Console.WriteLine("Addresses")
                    For i = 0 To addresses.Length - 1
                        Console.WriteLine("{0}", addresses(i).ToString())
                    Next i
                End If
            Catch e as SocketException
                Console.WriteLine("An exception occurred while processing the request: {0}", e.Message)
            End Try
        End Sub
    End Class
End Namespace

另請參閱

• 基於事件的非同步模式 (EAP)
• 事件為基礎的非同步模式概述