C# 如何检查网络连接？

How do I check for a network connection?

提问by Brad

What is the best way to determine if there is a network connection available?

确定是否有可用网络连接的最佳方法是什么？

采纳答案by Mitch Wheat

You can check for a network connection in .NET 2.0 using GetIsNetworkAvailable():

您可以使用以下命令检查 .NET 2.0 中的网络连接GetIsNetworkAvailable()：

System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable()

To monitor changes in IP address or changes in network availability use the events from the NetworkChangeclass:

要监视 IP 地址的更改或网络可用性的更改，请使用NetworkChange类中的事件：

System.Net.NetworkInformation.NetworkChange.NetworkAvailabilityChanged
System.Net.NetworkInformation.NetworkChange.NetworkAddressChanged

回答by Simon Mourier

The marked answer is 100% fine, however, there are certain cases when the standard method is fooled by virtual cards (virtual box, ...). It's also often desirable to discard some network interfaces based on their speed (serial ports, modems, ...).

标记的答案是 100% 好，但是，在某些情况下，标准方法会被虚拟卡（虚拟盒子，...）所欺骗。通常还需要根据速度（串行端口、调制解调器等）丢弃一些网络接口。

Here is a piece of code that checks for these cases:

这是检查这些情况的一段代码：

    /// <summary>
    /// Indicates whether any network connection is available
    /// Filter connections below a specified speed, as well as virtual network cards.
    /// </summary>
    /// <returns>
    ///     <c>true</c> if a network connection is available; otherwise, <c>false</c>.
    /// </returns>
    public static bool IsNetworkAvailable()
    {
        return IsNetworkAvailable(0);
    }

    /// <summary>
    /// Indicates whether any network connection is available.
    /// Filter connections below a specified speed, as well as virtual network cards.
    /// </summary>
    /// <param name="minimumSpeed">The minimum speed required. Passing 0 will not filter connection using speed.</param>
    /// <returns>
    ///     <c>true</c> if a network connection is available; otherwise, <c>false</c>.
    /// </returns>
    public static bool IsNetworkAvailable(long minimumSpeed)
    {
        if (!NetworkInterface.GetIsNetworkAvailable())
            return false;

        foreach (NetworkInterface ni in NetworkInterface.GetAllNetworkInterfaces())
        {
            // discard because of standard reasons
            if ((ni.OperationalStatus != OperationalStatus.Up) ||
                (ni.NetworkInterfaceType == NetworkInterfaceType.Loopback) ||
                (ni.NetworkInterfaceType == NetworkInterfaceType.Tunnel))
                continue;

            // this allow to filter modems, serial, etc.
            // I use 10000000 as a minimum speed for most cases
            if (ni.Speed < minimumSpeed)
                continue;

            // discard virtual cards (virtual box, virtual pc, etc.)
            if ((ni.Description.IndexOf("virtual", StringComparison.OrdinalIgnoreCase) >= 0) ||
                (ni.Name.IndexOf("virtual", StringComparison.OrdinalIgnoreCase) >= 0))
                continue;

            // discard "Microsoft Loopback Adapter", it will not show as NetworkInterfaceType.Loopback but as Ethernet Card.
            if (ni.Description.Equals("Microsoft Loopback Adapter", StringComparison.OrdinalIgnoreCase))
                continue;

            return true;
        }
        return false;
    }

回答by Saleh Rahimzadeh

Microsoft windows vista and 7 use NCSI (Network Connectivity Status Indicator) technic:

Microsoft windows vista 和 7 使用 NCSI（网络连接状态指示器）技术：

1. NCSI performs a DNS lookup on www.msftncsi.com, then requests http://www.msftncsi.com/ncsi.txt. This file is a plain-text file and contains only the text 'Microsoft NCSI'.
2. NCSI sends a DNS lookup request for dns.msftncsi.com. This DNS address should resolve to 131.107.255.255. If the address does not match, then it is assumed that the internet connection is not functioning correctly.

1. NCSI 在 www.msftncsi.com 上执行 DNS 查找，然后请求http://www.msftncsi.com/ncsi.txt。此文件是纯文本文件，仅包含文本“ Microsoft NCSI”。
2. NCSI 向 dns.msftncsi.com 发送 DNS 查找请求。此 DNS 地址应解析为 131.107.255.255。如果地址不匹配，则假定 Internet 连接未正常运行。

回答by Kumar

Call this method to check the network Connection.

调用此方法检查网络连接。

public static bool IsConnectedToInternet()
        {
            bool returnValue = false;
            try
            {

                int Desc;
                returnValue = Utility.InternetGetConnectedState(out Desc, 0);
            }
            catch
            {
                returnValue = false;
            }
            return returnValue;
        }

Put this below line of code.

将此放在代码行下方。

[DllImport("wininet.dll")]
        public extern static bool InternetGetConnectedState(out int Description, int ReservedValue);