What is the best way to check for Internet connectivity using .NET?

Question

What is the fastest and most efficient way to check for Internet connectivity in .NET?

Answer 1

I disagree with people who are stating: "What's the point in checking for connectivity before performing a task, as immediately after the check the connection may be lost". Surely there is a degree of uncertainty in many programming tasks we as developers undertake, but reducing the uncertainty to a level of acceptance is part of the challenge.

I recently ran into this problem making an application which including a mapping feature which linked to an on-line tile server. This functionality was to be disabled where a lack of internet connectivity was noted.

Some of the responses on this page were very good, but did however cause a lot of performance issues such as hanging, mainly in the case of the absence of connectivity.

Here is the solution that I ended up using, with the help of some of these answers and my colleagues:

         // Insert this where check is required, in my case program start
         ThreadPool.QueueUserWorkItem(CheckInternetConnectivity);
    }

    void CheckInternetConnectivity(object state)
    {
        if (System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable())
        {
            using (WebClient webClient = new WebClient())
            {
                webClient.CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.BypassCache);
                webClient.Proxy = null;
                webClient.OpenReadCompleted += webClient_OpenReadCompleted;
                webClient.OpenReadAsync(new Uri(""));
            }
        }
    }

    volatile bool internetAvailable = false; // boolean used elsewhere in code

    void webClient_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
    {
        if (e.Error == null)
        {
            internetAvailable = true;
            Dispatcher.Invoke(DispatcherPriority.Normal, new Action(() =>
            {
                // UI changes made here
            }));
        }
    }