public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        startService(new Intent(this, ServiceViewManager.class));

        setUI();
    }

    private void setUI()
    {
        LinearLayout layout = new LinearLayout(this);

        layout.setOrientation(LinearLayout.VERTICAL);

        layout.addView(createLoadUrlInvisible());
        layout.addView(createShowWebView());

        this.setContentView(layout);
    }


    private Button createLoadUrlInvisible()
    {
        Button button = new Button(this);

        button.setText("LoadUrlInvisible (Click first)");

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                WebPageServiceView.instance().loadUrlInvisible();

            }
        });

        return button;
    }


    private Button createShowWebView()
    {
        Button button = new Button(this);

        button.setText("ShowWebView (Click second)");

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                WebPageServiceView.instance().setVisibility(View.VISIBLE);
            }
        });

        return button;
    }
}




public class ServiceViewManager extends Service {

    private static ServiceViewManager inst = null;

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    public static ServiceViewManager Instance()
    {
        return inst;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        super.onStartCommand(intent, flags, startId);

        inst = this;

        return START_NOT_STICKY;
    }

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public void onDestroy() {

        inst = null;
        super.onDestroy();
    }


    public void add(final View view, final WindowManager.LayoutParams params)
    {
        ((WindowManager)getSystemService(Service.WINDOW_SERVICE)).addView(view, params);
    }
}



public class WebPageServiceView extends FrameLayout {

    private static WebPageServiceView inst = null;

    public WebPageServiceView() {
        super(ServiceViewManager.Instance());
    }


    public static WebPageServiceView instance() {

        if(inst == null)
            inst = new WebPageServiceView();

        return inst;
    }

    private void addViewToService()
    {
        WindowManager.LayoutParams serviceParams = new WindowManager.LayoutParams();
        serviceParams.x = 0;
        serviceParams.y = 0;

        serviceParams.type = WindowManager.LayoutParams.TYPE_PHONE;
        serviceParams.flags = WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;
        serviceParams.format = PixelFormat.TRANSPARENT;

        ServiceViewManager.Instance().add(this, serviceParams);
    }


    private void addWebViewAndLoadUrl()
    {
        WebView webView = new WebView(getContext());

        webView.loadUrl("http://naver.com");
        webView.setWebViewClient(new WebViewClient());

        this.addView(webView);
    }


    public void loadUrlInvisible() {

        addViewToService();

        addWebViewAndLoadUrl();

        setVisibility(INVISIBLE);
    }

}