Android Phonegap: Notify javascript when an AsyncTask is finished

Question

in my app, when user click on a button in webview, a phonegap plugin will be called to trigger an asynctask to download file from internet. Now i want to send a signal back

Answer 1

This is how I solve problems like your.

1) Create and associate a JavascriptInterface to your WebView. A JavascriptInterface is simply a class inside which you can declare some Java method you want to use from JS.

public class JSInterface() {
    private final CountDownLatch latch = new CountDownLatch(1);

    public void waitForProceed() {
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void canProceed() {
        latch.countDown();
    }
}

2) In your AsyncTask, at the end of onPostExecute() method, you have to call the canProceed() method to notify to JSInterface that it can exit from waitForProceed() method.

public class MyAsyncTask extends AsyncTask<.......> {
    private JSInterface jsi;
    ... // other class property

    public MyAsyncTask(JSInterface jsi) {
        ...
        //do what you want with other class property

        this.jsi = jsi;
    }

    @Override
    public ... doInBackground(...) {
        ...
        //do something
    }

    @Override
    public void onPostExecute(...) {
        ...
        //do something

        jsi.canProceed();
    }
}

3) In your Activity you have to associate the JSInterface object to your WebView:

WebView mWebView;

...

mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.addJavascriptInterface(new JSInterface(), "JSIface");

4) Finally, in JS, you can call AsyncTask (I don't know how you call it, but I guess you use somthing like a JSInterface) and after call waitForProceed() method:

startAsyncTask(); //somehow
JSIface.waitForProceed();

I hope it solves your problem ;)