There are a number of methods to detect network connectivity, all of which can be read about here, here, here and here. What I found is that these seem to work fine when there is an actual change in your network connection. eg disconnecting your wireless connection, unplugging a network cable or USB modem. But if there is just a drop in network connectivity, such as a break the router side, invisible to the user’s PC then these methods work less well.

When using a URL monitor in flex, it polls for a URL on first start, and then after that you can configure the poll interval depending on your needs. Unfortunately, this is far from ideal given that people are online more often than offline, and its just not great to poll some URL every few seconds when it really isn’t necessary.

My recent download manager application uses a URL monitor but it also has a timer running in the background for each download. Every 10 seconds it checks to see if the bytes downloaded has changed. The theory being that if even the slowest net connection has downloaded 0 bytes in 10 seconds, its safe to say there is probably a network problem. It then begins polling every 10 seconds until there is a response and then assumes the user is online again and the download can continue. This is done as follows….

Firstly I initiate a timer and update value using a progressEvent tied to my URLStream.

private function onDownloadProgress(event:ProgressEvent):void {
value = Math.round(event.bytesLoaded);
}

Then I compare the bytes downloaded to a running count as follows…

private function possibleNetworkProblem(e:TimerEvent):void {
if (lastLotOfBytes == value) {
lastLotOfBytes = 0;
sendNetworkError();
} else {
lastLotOfBytes = value
}
}

If the values have not changed then I disconnect and reconnect the URL monitor every 10 seconds until network returns….

private function sendNetworkError():void {
if (monitor.available) {
myTimer.stop();
myTimer.removeEventListener(TimerEvent.TIMER,possibleNetworkProblem);
initiateDownloads();
}
monitor.removeEventListener(StatusEvent.STATUS, announceStatus);
monitor.stop();
monitor.start();
monitor.addEventListener(StatusEvent.STATUS, announceStatus);
}