C＃线程和轮询

Question

I have a tray icon that needs to display two icons:

1. If there is network connectivity, display a green circle with a check mark
2. If there isn't network connectivity, display a red circle with an X

So what I have is:

using System.Net.NetworkInformation;

bool isConnected = NetworkInterface.GetIsNetworkAvailable()

So I'm thinking of starting a new thread or using the background worker progress because the tray icon is a NotifyIcon which is a component so I can't use:

Form.Invoke(delegate, object[])

to update the icon property of the NotifyIcon class.

My big concern is the polling process: I could write some logic that does:

while (true) 
{
    System.Threading.Thread.Sleep(1000);
    isConnected = NetworkInterface.GetIsNetworkAvailable();
    if (isConnected)
        notifyIcon.Icon = "ConnectedIcon.ico";
    else
        notifyIcon.Icon = "DisconnectedIcon.ico";
}

but I've seen a couple of articles that tell me to stay away from Sleep(1000). I can't seem to find those articles since I didn't bookmark them. I'm just curious to know why that isn't a good idea for polling in a thread.

Answer 1

You can register an Event on NetworkChange so you are being notified when the status changes:

NetworkChange.NetworkAvailabilityChanged += new NetworkAvailabilityChangedEventHandler(NetworkChange_NetworkAvailabilityChanged);

void NetworkChange_NetworkAvailabilityChanged(object sender, NetworkAvailabilityEventArgs e)  
{
    if (e.IsAvailable) {
        Console.WriteLine("Network Available");
    } else {
        Console.WriteLine("Network Unavailable");
    }
}

Answer 2

In you situation its totally fine to use the Sleep method.

What you saw was probably saying so its better to use a Reset Event - from looping etc...

Answer 3

Polling isn't always evil, but it's best avoided if possible. If I run your application that's polling once per second, that means that once per second your program is getting scheduled to do work on a CPU core that is 99.9999% going to be a no-op. On a desktop that's not too terrible, but imagine a laptop. CPUs there try run in very low power modes whenever possible, so additional CPU work means less battery life! This is the reason why many mobile platforms (iOS, Windows Phone 7, etc) ban arbitrary background threads because they know people will abuse them.

In your case, there's an easier way: just use System.Net.NetworkInformation.NetworkChange which provides events for when the network connectivity changes. No polling required!