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How can I see if a network connection changes state?

Answer 1

+2 A:

You should try System.Net.NetworkInformation namespace, or by using P/Invoke.

Samples:

Rubens Farias 2010-02-04 15:27:05

NetworkChange.NetworkAvailabilityChanged += new NetworkAvailabilityChangedEventHandler(NetworkChange_NetworkAvailabilityChanged); NetworkChange.NetworkAddressChanged += new NetworkAddressChangedEventHandler(NetworkChange_NetworkAddressChanged);

EricLaw -MSFT- 2010-02-04 15:35:22

Unfortunately, nothing in that namespace is able to tell you when your WiFi signal drops to zero level, for example. That is, when NetworkAvailabilityChanged event occurs with its IsAvaiable property set to false, you know for sure that you're disconnected. But you might be disconnected (someone cut your cable, for instance) and no events occur. That's the way TCP/IP is working.

Igor Korkhov 2010-02-04 15:37:22

Answer 2

A:

The only reliable way of doing it is to periodically check availability of some reliable external resource. You can, for example, ping your server, request some info, etc.

Igor Korkhov 2010-02-04 15:27:41

I am simply just pinging to see if our web proxy server responds, as the proxy configuration is what will be changed.My application is checking this every couple of minutes now, but I would love to make this happen instantly if the user connects to another network. :)

tkalve 2010-02-04 15:33:32

Then the Rubens' method is what you need. But remeber, your users might potentially be connected to your proxy and some external network *at the same time*. Then if they disconnect from you proxy, NetworkAvailabilityChanged will not be raised, provided they are still connected to the other network.

Igor Korkhov 2010-02-04 15:43:50

Answer 3

A:

[DllImport("wininet.dll", SetLastError=true)] 
public static extern bool InternetGetConnectedState(out int flags,int reserved);

Returns TRUE if there is an Internet connection, or FALSE otherwise

igor 2010-02-04 15:40:06

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How can I see if a network connection changes state?

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