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 with remote one and notify the users on new remote pushes etc . The point is I have this code implemented in javascript but I want execute it i background.
I searched internet for a cordova background service plugin.
The best one I think is red-folder but it is just for android and it does not let me to write javascript to be executed in background. but just exchange json between java and javascript.
I have read some topics about background service in android these are useful ones I found:
So I started writing cordova plugin (primarily on android) to execute the javascript code in background. I created a webview from the background service to execute the javascript from it. This works fine when I execute normal javascript but when it comes to cordova plugins js it fails for example the device device.uuid
gives null
.
This is the java service code:
public void onStart(Intent intent, int startId) {
Toast.makeText(this, "My Happy Service Started", Toast.LENGTH_LONG).show();
createBackGroundView();
super.onStart(intent,startId);
}
public void createBackGroundView(){
WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
LayoutParams params = new WindowManager.LayoutParams(
android.view.ViewGroup.LayoutParams.WRAP_CONTENT,
android.view.ViewGroup.LayoutParams.WRAP_CONTENT,
WindowManager.LayoutParams.TYPE_PHONE,
WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE,
PixelFormat.TRANSLUCENT
);
params.gravity = Gravity.TOP | Gravity.LEFT;
params.x = 0;
params.y = 0;
params.width = 200;
params.height = 200;
LinearLayout view = new LinearLayout(this);
view.setLayoutParams(new RelativeLayout.LayoutParams(
android.view.ViewGroup.LayoutParams.MATCH_PARENT,
android.view.ViewGroup.LayoutParams.MATCH_PARENT
));
WebView wv = new WebView(this);
wv.setLayoutParams(new LinearLayout.LayoutParams(
android.view.ViewGroup.LayoutParams.MATCH_PARENT,
android.view.ViewGroup.LayoutParams.MATCH_PARENT
));
view.addView(wv);
wv.getSettings().setJavaScriptEnabled(true);
wv.setWebChromeClient(new WebChromeClient());
wv.loadUrl("file:///android_asset/www/background.html");
wv.setWebViewClient(new WebViewClient() {
@Override
public void onReceivedError(final WebView view, int errorCode,
String description, final String failingUrl) {
Log.d("Error","loading web view");
super.onReceivedError(view, errorCode, description, failingUrl);
}
});
windowManager.addView(view, params);
}
Update There is no error in the logcat. So I tried to write the device object on the screen and thats what I get :
document.write(JSON.stringify(window.device))
And this is the result :
{ available : false,
plaform : null ,
version : null ,
uuid : null ,
cordova : null ,
model : null
}
I tried to replace the standard webView
with cordovaWebView
But the same result is given.
//WebView wv = new WebView(this); Commented out
CordovaWebView wv = new CordovaWebView(this);
Any help about this problem ?
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 .
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.
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);
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