使用 C# 检查 Internet 连接是否可用
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check whether Internet connection is available with C#
提问by
What is the easiest way to check whether internet connection is available programatically?
以编程方式检查互联网连接是否可用的最简单方法是什么？
EDIT: As suggested I tried using the following method, but it is always returning true.
编辑：正如我所建议的那样，我尝试使用以下方法，但它总是返回 true。
[Flags]
enum InternetConnectionState : int
{
INTERNET_CONNECTION_MODEM = 0x1,
INTERNET_CONNECTION_LAN = 0x2,
INTERNET_CONNECTION_PROXY = 0x4,
INTERNET_RAS_INSTALLED = 0x10,
INTERNET_CONNECTION_OFFLINE = 0x20,
INTERNET_CONNECTION_CONFIGURED = 0x40
}
class Program
{
[DllImport("WININET", CharSet = CharSet.Auto)]
static extern bool InternetGetConnectedState(ref InternetConnectionState lpdwFlags, int dwReserved);
static void Main(string[] args)
{
InternetConnectionState flags = 0;
bool isConnected = InternetGetConnectedState(ref flags, 0);
Console.WriteLine(isConnected);
//Console.WriteLine(flags);
Console.ReadKey();
}
}
Additional Info (if it helps): I access internet over a shared wifi network.
附加信息（如果有帮助）：我通过共享 wifi 网络访问互联网。
回答by colithium
Hereis the Windows API you can call into. It's in wininet.dll and called InternetGetConnectedState.
这是您可以调用的 Windows API。它位于 wininet.dll 中，名为InternetGetConnectedState。
using System;
using System.Runtime;
using System.Runtime.InteropServices;
public class InternetCS
{
//Creating the extern function...
[DllImport("wininet.dll")]
private extern static bool InternetGetConnectedState( out int Description, int ReservedValue );
//Creating a function that uses the API function...
public static bool IsConnectedToInternet( )
{
int Desc ;
return InternetGetConnectedState( out Desc, 0 ) ;
}
}
回答by Kibbee
Easiest way is to probably check if they can download a file from the web that you know is available. Use the following code to download google's homepage.
最简单的方法是检查他们是否可以从您知道可用的网络下载文件。使用以下代码下载谷歌主页。
WebClient Client = new WebClient ();
String Response;
Response = Client.DownloadString("http://www.google.com");
You should probably wrap that in a Try .... Catch to catch the exception that is thrown when it can't establish a connection.
您可能应该将其包装在 Try .... Catch 中以捕获无法建立连接时抛出的异常。
回答by mkchandler
You can check for a network connection using this in .NET 2.0+
您可以在 .NET 2.0+ 中使用它检查网络连接
System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable();
This will probably just return truefor local networks, so it may not work for you.
这可能只会返回true本地网络，因此它可能对您不起作用。
回答by Roger Willcocks
There are some other options too.
还有一些其他的选择。
The InfoPath library exposes the "IsDestinationReachable"method, which is a wrapper for the Win API method of the same name. (Looks like Vista doesn't support it)
InfoPath 库公开了“IsDestinationReachable”方法，它是同名 Win API 方法的包装器。（貌似Vista不支持）
However, I believe from the Docs that it depends on something like PING, so not necessarily a good test.
但是，我从文档中相信它取决于 PING 之类的东西，所以不一定是一个好的测试。
Vista + say use the "Network List Manager"
Vista + 说使用“网络列表管理器”
@colithium Google might not be down, but things can also fail out if the DNS lokup interval exceeds the timeout. Not uncommon at home here in NZ, first try fails, second succeeds because the data has propogated back to the ISP DNS or your router cache by the time the second request is done.
@colithium Google 可能不会宕机，但如果 DNS 查找间隔超过超时，事情也可能会失败。在新西兰的家里并不少见，第一次尝试失败，第二次成功，因为在第二次请求完成时数据已经传播回 ISP DNS 或您的路由器缓存。
回答by KristoferA
This is a question where the answer really is "it depends". Because it depends on why you want to check and for what kind of connectivity? Do you want to be able to access certain websites/services over http? Send smtp mail? Do dns lookups?
这是一个答案确实是“视情况而定”的问题。因为这取决于您为什么要检查以及哪种连接？您是否希望能够通过 http 访问某些网站/服务？发送smtp邮件？做dns查询？
Using a combination of the previous answers is probably the way to go - first use the wininet api from colithium's answer to check if a connection of any kind is available.
使用以前的答案的组合可能是要走的路 - 首先使用来自 colithium 的答案的 wininet api 检查是否有任何类型的连接可用。
If it is, try a couple of dns lookups (see System.Net.Dns ) for either the resources you're interested in or some popular big websites (google, altavista, compuserve, etc...).
如果是，请尝试对您感兴趣的资源或一些流行的大型网站（google、altavista、compuserve 等）进行几次 dns 查找（请参阅 System.Net.Dns ）。
Next, you can try pinging (see Roger Willcocks' answer) and/or establishing a socket connection to the same sites. Note that a failed ping could just mean that firewall rules don't allow you to ping.
接下来，您可以尝试 ping（参见 Roger Willcocks 的回答）和/或建立到相同站点的套接字连接。请注意，失败的 ping 可能仅意味着防火墙规则不允许您 ping。
If you can be more specific as to why you want to check it will be easier to provide an answer that covers your requirements...
如果您可以更具体地说明为什么要检查，那么提供满足您要求的答案会更容易...
回答by SolidSnake
here is the best solution I found so far:
这是我迄今为止找到的最佳解决方案：
public static bool isConnected()
{
try
{
string myAddress = "www.google.com";
IPAddress[] addresslist = Dns.GetHostAddresses(myAddress);
if (addresslist[0].ToString().Length > 6)
{
return true;
}
else
return false;
}
catch
{
return false;
}
}
usage:
用法：
if(isConnected())
{
//im connected to the internet
}
else
{
//not connected
}
回答by u109919
Network Awareness in Windows XP
Network Awareness in Windows Vista and Windows 7
Windows Vista 和 Windows 7 中的网络感知
Of course this does not guarantee the web site you plan to visit is not blocked by cooperative firewall rules, the API just checking if a pre-defined web site is reachable.
当然，这并不能保证您计划访问的网站不会被合作防火墙规则阻止，API 只是检查预定义的网站是否可访问。
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：
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'. 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.
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”。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 Faisal Shahzad
Alternatively you can use DNS lookup to check internet connectivity. This method is faster than Ping method.
或者，您可以使用 DNS 查找来检查互联网连接。这种方法比 Ping 方法快。
public static bool DnsTest()
{
try
{
System.Net.IPHostEntry ipHe =
System.Net.Dns.GetHostByName("www.google.com");
return true;
}
catch
{
return false;
}
}
