检测网络的连接状态

下面这段代码，返回当前计算机的网络连接状态

[DllImport("wininet.dll")]

private static extern bool InternetGetConnectedState(ref uint connected, uint reserved);



static uint uConnection = 0x20;



/// <summary>

/// Returns true if it have detected an active Internet connection.

/// </summary>

public static bool HasInternetConnection

{

get { return InternetGetConnectedState(ref uConnection, 0); }

}



另：

To check for an
Internet connection in .NET, we can use GetIsNetworkAvailable method
defined in the System.Net.Network-Information namespace. But it returns
a Boolean value that denotes whether any network connection is
available and does not say about Internet connectivity. To make sure we
also have Internet access, the reliable method is to attempt to ping a
host

...
using System.Net.NetworkInformation;
...
public bool IsConnectedToInternet()
        {
            string host = http://www.c-sharpcorner.com;
            bool result = false;
            Ping p = new Ping();
            try
            {
                PingReply reply = p.Send(host, 3000);
                if (reply.Status == IPStatus.Success)
                    return true;
            }
            catch { }
            return result;
        }

Or we can use a simple API function InternetGetConnectedState. This function takes two arguments:

The first one is an integer used with out
keyword, which means that after calling the function, the variable will
contain an integer that describes the connection state.

The second one is a reserved variable that must be set to 0.

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 ) ;
}
}