How to run cordova plugin in Android background service?

Question

I am working on mobile application developed on cordova . I want to implement a background service that do some work like open socket connection syncronise local database wi

Answer 1

You should use an embedded Cordova WebView, not a standard WebView. A standard WebView is not set up to handle Cordova plugins, and the device info is a plugin.

See the Cordova docs on embedding webviews.

Answer 2

WebViews can not execute javascript from a background service.

I would recommend using native code instead. But if you must use javascript, i would try this library

https://code.google.com/p/jav8/

ScriptEngineManager factory = new ScriptEngineManager();
ScriptEngine engine = factory.getEngineByName("jav8");

  try {
    engine.eval("print('Hello, world!')");
  } catch (ScriptException ex) {
      ex.printStackTrace();
  } 

First load the contens of your script into a string and then run engine.eval() method.

Example (Run "test.js" from assets):

AssetManager am = context.getAssets();
InputStream is = am.open("test.js");
BufferedReader r = new BufferedReader(new InputStreamReader(is));
StringBuilder total = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
    total.append(line);
}

ScriptEngineManager factory = new ScriptEngineManager();
ScriptEngine engine = factory.getEngineByName("jav8");

  try {
    engine.eval(total.toString());
  } catch (ScriptException ex) {
      ex.printStackTrace();
  }

Notice! The eval function expects only a javascript function to be executed at a time and returns the value of this function.

Answer 3

To work with Cordova plugins in WebView as background service, i've created class that implements CordovaInterface. Here is an example

 private class CordovaBackground extends Activity implements CordovaInterface {
    private ArrayList pluginEntries = new ArrayList();
    private CordovaPreferences preferences;
    private Context context;
    private Whitelist internalWhitelist;
    private Whitelist externalWhitelist;
    private CordovaWebViewBackground webView;
    protected LinearLayout root;
    private WindowManager serviceWindowManager;
    private final ExecutorService threadPool = Executors.newCachedThreadPool();

    public CordovaBackground(Context context, WindowManager windowManager) {
        attachBaseContext(context);
        this.context = context;
        this.serviceWindowManager = windowManager;
    }

    private void loadConfig() {
        ConfigXmlParser parser = new ConfigXmlParser();
        parser.parse(this);
        preferences = parser.getPreferences();
        internalWhitelist = parser.getInternalWhitelist();
        externalWhitelist = parser.getExternalWhitelist();;
        ArrayList<PluginEntry> allPluginEntries = parser.getPluginEntries();
        String[] backgroundPluginNames = {"File"};//not all plugins you need in service, here is the list of them
        ArrayList<String> backgroundPlugins = new ArrayList<String>(
            Arrays.asList(backgroundPluginNames));
        for (PluginEntry pluginEntry : allPluginEntries) {
            if (backgroundPlugins.contains(pluginEntry.service)) {
                pluginEntries.add(pluginEntry);
            }
        }
    }

    public void loadUrl(String url) {
        init();
        webView.loadUrl(url);
    }

    public void init() {
        loadConfig();
        webView = new CordovaWebViewBackground(context);
        if (webView.pluginManager == null) {
            CordovaWebViewClient webClient = webView.makeWebViewClient(this);
            CordovaChromeClientBackground webChromeClient = webView.makeWebChromeClient(this);
            webView.init(this, webClient, webChromeClient,
                    pluginEntries, internalWhitelist, externalWhitelist, preferences);
        }
    }

    public WindowManager getWindowManager() {
        return serviceWindowManager;
    }

    @Override
    public void startActivityForResult(CordovaPlugin command, Intent intent, int requestCode) {
    }

    @Override
    public void setActivityResultCallback(CordovaPlugin plugin) {
    }

    @Override
    public Activity getActivity() {
        return this;
    }

    @Override
    public Object onMessage(String id, Object data) {
        return null;
    }

    @Override
    public ExecutorService getThreadPool() {
        return threadPool;
    }

    @Override
    public Intent registerReceiver(android.content.BroadcastReceiver receiver, android.content.IntentFilter filter) {
        return  getIntent();
    }

    @Override
    public String getPackageName() {
        return context.getPackageName();
    }

}

To prevent errors while cordova initializing, i've overrode onJsAlert method. If you have a time, you may have found better way.

 private class CordovaWebViewBackground extends CordovaWebView {

    public CordovaWebViewBackground(Context context) {
        super(context);
    }

    public CordovaChromeClientBackground makeWebChromeClient(CordovaInterface cordova) {
        return new CordovaChromeClientBackground(cordova, this);
    }

}

private class CordovaChromeClientBackground extends CordovaChromeClient {

    public CordovaChromeClientBackground(CordovaInterface ctx, CordovaWebView app) {
        super(ctx, app);
    }

    public boolean onJsAlert(WebView view, String url, String message, final JsResult result) {
        //super.onJsAlert(view, url, message, result);
        return true;
    }

}

How to use:

WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
CordovaBackground cordovaBackground = new CordovaBackground(this, wm);
cordovaBackground.setIntent(intent);
String url = "file:///android_asset/www/test.html";
cordovaBackground.loadUrl(url);