ConnectionManager not giving network callbacks when using `TRANSPORT_CELLULAR`

Question

Update: it does work: TRANSPORT_CELLULAR connections are only available when TRANSPORT_WIFI is disconnected. You will not receive callbacks when WiFi is enabled unless you have enabled simultaneous cellular data in the phone's Developer Settings.

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I'm trying to receive callbacks whenever the phone's cellular data connection changes. I essentially need to know when it turns off and when it turns on.

I used to do this with the TelephonyManager and PhoneStateListener.LISTEN_SERVICE_STATE, but now I want to use the ConnectionManager with registerNetworkCallback.

The following code sample has been tried on an Android Emulator (API 28), A HUAWEI P20 Lite (API 26), an HTC One M8 (API 23), and a Motorola G6 (API 26). None of them call any callbacks when I switch mobile data on/off, or activate airplane mode.

People say this should work.

    NetworkRequest.Builder builder = new NetworkRequest.Builder();

    builder.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
    builder.addTransportType(NetworkCapabilities.TRANSPORT_CELLULAR);

    connManager.registerNetworkCallback(builder.build(), new ConnectivityManager.NetworkCallback() {
        @Override
        public void onAvailable(Network network) {
            Log.d("Conman Test", "onAvailable");
        }

        @Override
        public void onLost(Network network) {
            Log.d("Conman Test", "onLost");
        }

        @Override
        public void onUnavailable() {
            Log.d("Conman Test", "onUnavailable");
        }

        @Override
        public void onCapabilitiesChanged(Network network, NetworkCapabilities networkCapabilities) {
            Log.d("Conman Test", "onCapabilitiesChanged");
        }

        @Override
        public void onLinkPropertiesChanged(Network network, LinkProperties linkProperties) {
            Log.d("Conman Test", "onLinkPropertiesChanged");
        }
    });

I have tried NetworkCapabilities.TRANSPORT_WIFI, and it works fine on all the devices. So why not NetworkCapabilities.TRANSPORT_CELLULAR?

Answer 1

I haven't tried to solve this problem using NetworkCapabilities , but I used an alternative approach to determine whether my device is connected via cellular or wifi.

I just registered a receiver

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

I added the permission

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

And then I did the following

public class NetworkChangeReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        ConnectivityManager cm =
                (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        boolean isConnected = activeNetwork != null &&
                activeNetwork.isConnectedOrConnecting();

        if(activeNetwork ==null){
            Log.d("Connectivity","Not connected");
            return;
        }

        boolean isWiFi = activeNetwork.getType() == ConnectivityManager.TYPE_WIFI;

        if(isConnected  && isWiFi){
            Log.d("Connectivity","WIFI");
        }else{
            Log.d("Connectivity","CELLULAR");
        }
    }
}

For Oreo device you may need to register receiver in activity or service rather than manifest

As an example

public class MainActivity extends Activity {

    IntentFilter filter1;

    @Override
    public void onCreate() {
        filter1 = new IntentFilter("android.net.conn.CONNECTIVITY_CHANGE");
        registerReceiver(myReceiver, filter1);
    }

    //The BroadcastReceiver that listens for network change
    private final BroadcastReceiver myReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if(intent.getAction().equalsIgnoreCase("android.net.conn.CONNECTIVITY_CHANGE")) {
                Log.d(TAG,"connectivity change");

             ConnectivityManager cm =
            (ConnectivityManager)this.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        boolean isConnected = activeNetwork != null &&
                activeNetwork.isConnectedOrConnecting();

        if(activeNetwork ==null){
            Log.d("Connectivity","Not connected");
            return;
        }

        boolean isWiFi = activeNetwork.getType() == ConnectivityManager.TYPE_WIFI;

        if(isConnected  && isWiFi){
            Log.d("Connectivity","WIFI");
        }else{
            Log.d("Connectivity","CELLULAR");
        }
            }
        }
    };

    @Override
    public void onDestroy() {
        unregisterReceiver(myReceiver);
    }
}