Force Android to Use Wifi network with no internet

Question

I am building an android app that needs to communicate over a WiFi network that will not have any internet access. The problem is that even when the WiFi is connected android chooses to use cellular/mobile data when no connection internet is present on the wifi network.

I have read many posts on the issue many of which involve rooting the device but that is not possible with a production app (rooting devices is not an option). other solution (like my code bellow) suggest using bindProcessToNetwork() which works perfectly on my Sony Z2 but not on other devices I have tested on (all running 6.0.1)

private void bindToNetwork() {
    final ConnectivityManager connectivityManager = (ConnectivityManager) mActivity.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkRequest.Builder builder;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        builder = new NetworkRequest.Builder();
        //set the transport type do WIFI
        builder.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);
        connectivityManager.requestNetwork(builder.build(), new ConnectivityManager.NetworkCallback() {
            @Override
            public void onAvailable(Network network) {
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {


                    connectivityManager.bindProcessToNetwork(null);
                    if (barCodeData.getSsid().contains("ap-name")) {
                        connectivityManager.bindProcessToNetwork(network);
                    }

                } else {
                    //This method was deprecated in API level 23
                    ConnectivityManager.setProcessDefaultNetwork(null);
                    if (barCodeData.getSsid().contains("ap-name")) {

                        ConnectivityManager.setProcessDefaultNetwork(network);
                    }
                }

                connectivityManager.unregisterNetworkCallback(this);
            }
        });
    }
}

Answer 1

Could you try and set the global setting captive_portal_detection_enabled to 0 (false).

What's actually happening is that by default, everytime you connect to a wifi, the FW will test against a server (typically google) to see if it's a captive wifi (needs login). So if your wifi is not connected to google, this check will fail. After that, the device knows that wifi has no internet connection and simply will not autoconnect to it.

Setting this setting to 0, will avoid this check.

Programatically: Settings.Global.putInt(getContentResolver(), Settings.Global.CAPTIVE_PORTAL_DETECTION_ENABLED, 0);

Edit: You may need to use the string "captive_portal_detection_enabled" directly, instead of the constant that's not visible depending on Android version.