Triggering javascript event from android

Question

I have created a cordova application. I am running an background service to perform some native task in the application. I need to trigger a java-script event once the background service complete its task. Is it possible to trigger js events from android?. Not able to find any solid answers for this. I need events because the application wound wait for the task in background service to complete. I want to event to notify the application that the task is complete. Is there any better way to implement this logic?.

Answer 1

Cordova itself doesn't expose its webview properties publicly for use by other Java classes, but you can do this with a minimal Cordova plugin which would allow your background service to access the Cordova webview in order to execute javascript in it from the Java layer. Then it's just a question of injecting the JS to trigger an event.

First you'd create a Cordova plugin to expose the necessary elements of Cordova to your background service:

public class MyPlugin extends CordovaPlugin{
    private static final String TAG = "MyPlugin";
    static MyPlugin instance = null;
    static CordovaWebView cordovaWebView;
    static CordovaInterface cordovaInterface;

    @Override
    public void initialize(CordovaInterface cordova, CordovaWebView webView) {
        super.initialize(cordova, webView);

        instance = this;
        cordovaWebView = webView;
        cordovaInterface = cordova;
    }

    @Override
    public void onDestroy() {
        instance = null;
    }

    private static void executeGlobalJavascript(final String jsString) {
        if (instance == null) {return;}
        instance.cordovaInterface.getActivity().runOnUiThread(new Runnable() {
            @Override
            public void run() {
                try {
                    instance.cordovaWebView.loadUrl("javascript:" + jsString);
                } catch (Exception e) {
                    Log.e(TAG, "Error executing javascript: "+ e.toString());
                }
            }
        });
    }

    public static void triggerJavascriptEvent(final String eventName){
        executeGlobalJavascript(String.format("document.dispatchEvent(new Event('%s'));", eventName));
    }
}

Then your background service can call the public method exposed by that plugin class:

public class MyService {
    public static void myMethod(){
        MyPlugin.triggerJavascriptEvent("myserviceevent");
    }
}

And finally, in your Cordova app's JS layer, you'd listen for your custom event:

document.addEventListener('myserviceevent', function(){
    console.log("myserviceevent received");
}, false);

I've created an example Cordova project which contains the minimal custom plugins required to achieve this which you can download here: http://ge.tt/8UeL6lu2

Once downloaded, unzip then:

cd cordova-test
cordova platform add android
cordova run android