Testing Internet Connectivity
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Some of the functions of our applications may require a run-time test of internet connectivity. Once internet connectivity is detected, the functions that require internet access may temporarily be disabled and/or the user can be notified via an alert message.
Introduction
Some of the functions of our applications may require a run-time test of internet connectivity. Once internet connectivity is detected, the functions that require internet access may temporarily be disabled and/or the user can be notified via an alert message. Otherwise, the application may result in error during operation or it may cause annoying problems for the user. In this article, I will try to demonstrate a couple of ways to overcome this problem.Method 1: WebRequest
We may send a web request to a website which assumed to be online always, for example google.com. If we can get a response, then obviously the device that runs our application is connected to the internet. public static bool WebRequestTest()
{
string url = "http://www.google.com";
try
{
System.Net.WebRequest myRequest = System.Net.WebRequest.Create(url);
System.Net.WebResponse myResponse = myRequest.GetResponse();
}
catch (System.Net.WebException)
{
return false;
}
return true;
}
Method 2: TCP Socket
There can be some delay in response of web request therefore this method may not be fast enough for some applications. A better way is to check whether port 80, default port for http traffic, of an always online website.
public static bool TcpSocketTest()
{
try
{
System.Net.Sockets.TcpClient client =
new System.Net.Sockets.TcpClient("www.google.com", 80);
client.Close();
return true;
}
catch (System.Exception ex)
{
return false;
}
}
Method 3: Ping
There can be some delay in response of web request, therefore this method may not be fast enough for some applications. A better way is to check whether port 80, default port for http traffic, of an always online website.public bool PingTest()
{
System.Net.NetworkInformation.Ping ping = new System.Net.NetworkInformation.Ping();
System.Net.NetworkInformation.PingReply pingStatus =
ping.Send(IPAddress.Parse("208.69.34.231"),1000);
if (pingStatus.Status == System.Net.NetworkInformation.IPStatus.Success)
{
return true;
}
else
{
return false;
}
}
You cannot use this method in .NET Compact Framework because there is no NetworkInformation namespace that comes with Compact Framework. However, you can use Smart Device Framework (http://www.opennetcf.com[^], Community Edition is free for download) provided by OpenNETCF. This framework comes with many other useful tools that .NET Compact Framework does not contain.
Notice that I used Google’s IP address 208.69.34.231. We could use Google’s web address www.google.com:
System.Net.NetworkInformation.PingReply pingStatus = ping.Send("www.google.com",1000);
However, that will require DNS lookup which causes extra delay.
Method 4: DNS Lookup
Alternatively you can use DNS lookup to check internet connectivity. This method is faster than Ping method. public static bool DnsTest()
{
try
{
System.Net.IPHostEntry ipHe =
System.Net.Dns.GetHostByName("www.google.com");
return true;
}
catch
{
return false;
}
}
Method 5: Windows Internet API (WinINet)
WinINet API provides functions to test internet connectivity, such as InternetCheckConnection and InternetGetConnectedState. I do not have any idea about what these fucntions do exactly to test internet connectivity. You may refer to http://msdn.microsoft.com/en-us/library/aa384346(v=VS.85).aspx and http://msdn.microsoft.com/en-us/library/aa384702(v=VS.85).aspx for details.
An example usage can be:
[DllImport("wininet.dll")]
private extern static bool InternetGetConnectedState(out int connDescription, int ReservedValue);
//check if a connection to the Internet can be established
public static bool IsConnectionAvailable()
{
int Desc;
return InternetGetConnectedState(out connDesc, 0);
}