Check internet connection with InternetGetConnectedState always true

Question

I need to check in my Compact Framework app if it has internet connection.

So looking around I found the InternetGetConnectedState method, but in my case every time I check if I have internet connection it returns true, even when I am offline.

Here is the code:

[DllImport("wininet.dll", CharSet = CharSet.Auto)]
private extern static bool InternetGetConnectedState(ref InternetConnectionState_e lpdwFlags, int dwReserved);

[Flags]enum InternetConnectionState_e : int
{
    INTERNET_CONNECTION_MODEM = 0x01,
    INTERNET_CONNECTION_LAN = 0x02,
    INTERNET_CONNECTION_PROXY = 0x04,
    INTERNET_RAS_INSTALLED = 0x10,
    INTERNET_CONNECTION_OFFLINE = 0x20,
    INTERNET_CONNECTION_CONFIGURED = 0x40
}

public Form1()
{
    InitializeComponent();
    verify();
}

private void verify()
{
    // In function for checking internet
    InternetConnectionState_e flags = 0;
    bool isConnected = InternetGetConnectedState(ref flags, 0);
    textBox1.Text = "Con: " + isConnected.ToString();
    textBox1.Text += "\r\nDescr: " + flags.ToString();
}

private void button1_Click(object sender, EventArgs e)
{
    verify();
}

private void button2_Click(object sender, EventArgs e)
{
    this.Close();
}

I am doing something wrong?

Answer 1

It looks like your P/Invoke internetgetconnectedstate signature might be a little off.

Copying from the link above, the signature appears to look for an int as the first parameter:

[DllImport("wininet.dll", SetLastError=true)]
extern static bool InternetGetConnectedState( out int lpdwFlags Description, int dwReserved );

[Flags]
enum ConnectionStates
{
    Modem = 0x1,
    LAN = 0x2,
    Proxy = 0x4,
    RasInstalled = 0x10,
    Offline = 0x20,
    Configured = 0x40,
}

The example code usage appears simple enough:

using System;
using System.Runtime.InteropServices;

namespace ConsoleApplication2
{
  internal class Program
  {
   [DllImport("wininet.dll", SetLastError = true)]
   private static extern bool InternetGetConnectedState(out int lpdwFlags, int dwReserved);

   private static void Main(string[] args)
   {
    int flags;
    bool isConnected = InternetGetConnectedState(out flags, 0);
    Console.WriteLine(string.Format("Is connected :{0} Flags:{1}", isConnected, flags));
   }
  }
}

What errors are you getting? You could always wrap the InternetGetConnectedState method in a try...catch block:

   private static void Main(string[] args)
   {
    int flags;
    bool isConnected = false;
    try
    {
      isConnected = InternetGetConnectedState(out flags, 0);
    } catch (Exception err)
    {
      Console.WriteLine(err.Message);
    }
    Console.WriteLine(string.Format("Is connected :{0} Flags:{1}", isConnected, flags));
   }
  }

Hope that helps.

UPDATE Based on your flags = 18 results:

flags is defined as an int, so 18 is a Decimal representation.

In Binary, this would be 0001 0010, which would map to LAN (0x2) | RasInstalled (0x10).

So, I'm guessing you are connected via a Local Area Network, but it does not guarantee the LAN has Internet Access. To test that, you would need to try to browse to a known good site.

RAS I am not sure about. Remote Access Service?

Keep in mind: A device cradled/docked in the charger could register as Connected, too.