Call javascript function from Java

Question

I develop an app using PhoneGap. I got a service which is in background and is coded natively (the service and the phone gap app is in the same project). Unfortunatly, I want to call a javascript function from this service. So I searched on the Web and founded something interesting : create a class extending Plugin and do some treatment in it. Then I found this :

this.ctx.sendJavascript("myJavascriptFunction");

I tested with this code, but something wrong happened :

java.lang.NullPointerException

Here is how I tested :

class c = new class();
c.execute("myFunction",null,null);

In the class c, the execute method is like this :

public PluginResult execute(String action, JSONArray args, String callbackId) {
if (action.equals("myFunction")){
    Log.d(TAG,"start actions to do");
    this.ctx.sendJavascript("nameOfFunctionToLaunch");
    Log.d(TAG,"end actions to do");
    return new PluginResult(PluginResult.Status.OK);
}
}

When the app start, I have the first

Log.d(TAG,"start actions to do");

How can I solve this problem ?

Answer 1

Finally I found the solution : in fact the NullPointerException was on ctx. To fix it, I setup the Context value of my object c like this :

c.setContext(use_An_Object_Of_Type_PhonegapActivity);

To get the object, I grab it from the AppActivity in this method :

public class CloudPhoneAppActivity extends DroidGap {
private class NoScaleWebViewClient extends GapViewClient {

    public NoScaleWebViewClient(DroidGap ctx) {
        super(ctx);
        myApp.ctx = ctx;
    }

    public void onScaleChanged(WebView view, float oldScale, float newScale) {
        Log.d("NoScaleWebViewClient", "Scale changed: " + String.valueOf(oldScale) + " => " + String.valueOf(newScale));
    }
}
/** other stuff after**/ 
}

So finally here is the solution :

class c = new class();
c.setContext(myApp.ctx);
c.execute("myFunction",null,null);

There is no change to do in the execute method which is describe before. But be careful of how you call the javascript function.

Erwan