Android Offline Request with Volley

Question

I want to give to my user a much better offline user experience, therefore, I want to build a Service which stores all POST, DELETE, PUT (GET makes no sense because a GET call without network is a cache call) requests the user does offline and send them to the server as soon as the user got an internet connection. I want it to be persistent: even if the app is killed, data are sent in order not to have inconstancies between cache and server data.

I'm quite familiar with Google Volley and Android Networking API --> I know how to detect there is no network, how to prefetch data, to cache them etc...

But is there a gist or a library about this subject? I know that the latest Facebook version implements such a system but I wonder how they did (I mean, I know there're using a Service but how they exactly did, got no idea!). Does someone has idea on that, any experience?

Answer 1

You need to use a BroadcastReceiver to listen to network change events. Define a broadcastReciver in your AndroidManifest.xml with the following action.

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

Also add the following permissions as well to your manifest file -

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

NetworkBroadcastReceiver -

public class NetworkBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(final Context context, final Intent intent) {

        if(isInternetConnected(context)) {
            //Do something i.e. trigger an API call or start a IntentService etc.
        }    
    }


    public boolean isInternetConnected(Context context) {
        ConnectivityManager connectivityManager 
            = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
        return activeNetworkInfo != null && activeNetworkInfo.isConnected();
    }    
}

That's all you need to do to make a request as soon as you get Internet.

To cache data, I'll advise you to parse the server response and keep it in your database for offline use. Every time you make a successful request save the new data in database and discard the old one. When user starts the app, load the data from database first and then trigger the Volley request, if request become successful then load the new data in app, store it in database and get rid of the old one. So in case if request fails, user will still be able to see the old data from previous successful request.

To handle inconsistency between data in app and server, you need to use SyncAdapter. SyncAdapter provide a great support for periodic sync in the background. Just put the syncing code in onPerformSync() method of SyncAdapter. It might not work in following two scenarios - 1. If user isn't connected to internet 2. If user device is turned off

To handle these scenario, use the BroadCastReceiver that I explained above in my answer to trigger the SyncAdapter. Also add the following actions to your receiver inside AndroidManifest.xml to listen to boot complete event of device.

<action android:name="android.intent.action.BOOT_COMPLETED" />
<action android:name="android.intent.action.QUICKBOOT_POWERON" />

Let me know if you need more in depth explanation with coding example. Hope it helps