Android M - Sending request over WiFi without connection when Mobile data is ON with connection

Question

I need to send UDP packets to a WiFi module (provided with my own AP) with no internet connection but when I connect the mobile with the AP, it redirects my packets on the mobile data interface because it finds an internet connection.
This is my code for it, but it's not working on Android M:

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
private void setWifiInterfaceAsDefault() {
    ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

    NetworkRequest.Builder builder = new NetworkRequest.Builder();
    NetworkRequest networkRequest= builder.addCapability(NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED)
            .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
            .build();

    connectivityManager.requestNetwork(networkRequest, new ConnectivityManager.NetworkCallback());
}

I also added:

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

..to my AndroidManifest.xml and I ensured that Settings.System.canWrite(this) returns true but something still seems to be wrong.

Help! TIA!

Answer 1

Binding the network using ConnectivityManager.setProcessDefaultNetwork() will help to prevent roaming and allows for full TCP access. Thus, within the onAvailable() callback you could bind the application process to that network rather than opening a connection to a particular URL.

ConnectivityManager connection_manager = 
(ConnectivityManager) activity.getApplication().getSystemService(Context.CONNECTIVITY_SERVICE);

NetworkRequest.Builder request = new NetworkRequest.Builder();
request.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);

connection_manager.registerNetworkCallback(request.build(), new NetworkCallback() {

    @Override
    public void onAvailable(Network network) {
        ConnectivityManager.setProcessDefaultNetwork(network);
    }
}