不断检查互联网连接

Question

I'm developing an Android app with ionic framework and need to check the internet connection, but steadily. For example if the user is logged in and then has no connection, I would like to display a message or any message. I had thought something like

<div class="bar bar-subheader" id="alerta_no_internet" ng-show="!online">
    <p>Not connected to Internet </p>
</div

What they do not do is any service or if there is something to be constantly asking about the connection.

Answer 1

There are a few ways of going about this:

1. You can store an asset (maybe a 1px x 1px GIF image) on your server and constantly keep polling for this (continuous requests every x seconds). Of course you wanna make sure this image is not cached. If the request fails, you can assume that the network is not available. This is easy to implement, but is not efficient because polling sends tons of HTTP headers over the wire.
2. This is much more efficient - implement a WebSocket connection in your client and server and open a socket upon opening the app. If the socket drops, you can display the Connectivity Lost message. This doesn't require sending of HTTP requests repeatedly. This is much more efficient, but more work will be required to implement this.

You can write services for either of these in Ionic.

At it's simplest, option #1 can be:

setInterval(ajaxCall, 3000); //3000 MS == 3 sec

function ajaxCall() {
  $.ajax('/testConnectivityUrl').then(function(response) {
    console.log("Still connected");
  }, function(err) {
    console.log("Lost connection");
  }
}

I've used jQuery, but you can do this with vanilla JS or Angular or Ionic services or factories.

Answer 2

I don't know much about the ionic framework, but the ConnectivityManager in the Android framework does emit a broadcast on connectivity changes . You can implement a BroadcastReceiver to listen for these changes:

<receiver android:name=".ConnectivityReceiver">
    <intent-filter>
        <action android:name="android.net.conn.CONNECTIVITY_CHANGE"/>
    </intent-filter>
</receiver>

Then access the ConnectivityManager to monitor the state of the network :

public class ConnectivityReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        ConnectivityManager manager =
                (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo info = manager.getActiveNetworkInfo();

        // TODO: monitor state using NetworkInfo

    }

}

Make sure you declare the internet and network state permissions in the Manifest as well:

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

Be aware though that connectivity changes can be frequent, therefore monitoring them can be costly. According to best practices you should toggle this receiver on only when it is needed:

It's generally sufficient to simply check for Internet connectivity before beginning an update and, should there be none, suspend further updates until connectivity is restored.