android - keepRunning PhoneGap/Cordova

Question

Anyone can explain me how keepRunning works in the config.xml for Android.

I mean, I don't want to know how to write the instruction but how does it work, how does it affect the execution of the Android app ? Does it create an Service in background ?

If anyone can find the source where we can see how does it work, that will be great

Thanks.

Edit : I try to analyze the generated code, analyze the RAM, services and processus in the setting of Android. And my conclusion is..... that do nothing. If you try to make a app which track the user with GPS, dont use Cordova. To track the user correctly, you need to make a Service with the START_STICKY option. So, it's in native code. you lost the interest of the CrossPlatform because you have to recode the service for all platforms and in my opinion, the communication between Native Service and Cordova App is not easy.

In conlusion, if you use Cordova, you have to know you can't use the power of all native, you have to make choise : - easy dev (subjective) and crossplaform (really crossplatform ?) and - Native dev with its power and no compatibility problems but you have to make one app for one platform

Answer 1

I'm not a JS/Cordova developer, I'm an Android developer. Once I worked on a Cordova plugin, faced some issues and did some investigations on the subject.

General purpose of keepRunning flag is to indicate if JS timers should be stopped when the app is paused (goes to background). Answering your question: no, it doesn't create any new Service. Existing design is quite plain in this regard.

The keepRunning flag is defined in CordovaActivity.java as follows:

// Keep app running when pause is received. (default = true)
// If true, then the JavaScript and native code continue to run in the background
// when another application (activity) is started.
protected boolean keepRunning = true;

Its main purpose is to disable JS timers when Cordova app is paused, in CordovaWebView.java:

public void handlePause(boolean keepRunning)
{
    LOG.d(TAG, "Handle the pause");
    // Send pause event to JavaScript
    this.loadUrl("javascript:try{cordova.fireDocumentEvent('pause');}catch(e){console.log('exception firing pause event from native');};");

    // Forward to plugins
    if (this.pluginManager != null) {
        this.pluginManager.onPause(keepRunning);
    }

    // If app doesn't want to run in background
    if (!keepRunning) {
        // Pause JavaScript timers (including setInterval)
        this.pauseTimers();
    }
    paused = true;

}

Note that plugins are also notified via PluginManager, so in theory they can handle app paused events, to stop (or not) their activity in background, depending on keepRunning flag.

In my case I had an issue/bug when keepRunning was true, but JS timers were stopped anyway. It happened because there is additional functionality related to that flag, in CordovaActivity.java:

/**
 * Launch an activity for which you would like a result when it finished. When this activity exits,
 * your onActivityResult() method will be called.
 *
 * @param command           The command object
 * @param intent            The intent to start
 * @param requestCode       The request code that is passed to callback to identify the activity
 */
public void startActivityForResult(CordovaPlugin command, Intent intent, int requestCode) {
    this.activityResultCallback = command;
    this.activityResultKeepRunning = this.keepRunning;

    // If multitasking turned on, then disable it for activities that return results
    if (command != null) {
        this.keepRunning = false;
    }

    // Start activity
    super.startActivityForResult(intent, requestCode);
}

When Cordova app launches another Android activity, main Cordova activity (screen with WebView) goes to background and is therefore paused. In my case it was made via Google Maps plugin which started GM screen over Cordova app.

The code above turns off keepRunning flag, and it means that JS timers are stopped anyway when the called activity appears (in CordovaActivity.onPause method) regardless keepRunning is true or false!

It looks like a kind of trick implemented for some unclear (and not documented) purpose, I do not know its context. In my case it caused a bug, and I just removed keepRunning handling in startActivityForResult, recompiled Cordova and it worked OK.

ADDED: About using a Service for GPS - you are quite right, I agree. As an Android developer with relevant (GPS) experience I can say that a right approach (and possible the only acceptable) is to use a service for that. As far as I know Cordova doesn't provide any functionality for it, so I think it should be made via a plugin. I mean you can write native Android code for GPS functionality (implemented as a Service) and access it from JS code. I believe it is a common solution in Cordova for such cases.