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 ?

Have you tried navigating to a JavaScript URL like `javascript:someFunction();`? — dtanders, Jan 11 '12 at 14:32
Many threads on the Web say that it is not the way to do it. Plus, I don't understand why, but I do not have the capability to use something like that : `object.loadUrl("javascript:function();");` — Erwan, Jan 11 '12 at 14:38

score 1 · Accepted Answer · answered Jan 12 '12 at 08:32

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

score 0 · Answer 2 · answered Jan 12 '12 at 06:42

You cant call object.loadUrl("javascript:function();"); from the plugin as plugin doesnt extend the WebView of Android. To call loadUrl you would have to pass the call back to the Home class which extends DroidGap.

In the plugin you can define

Home home = null;
Looper.prepare();
home = new Home();
home.somefunc();

and in somefunc call

super.loadUrl("javascript:function();");

Call javascript function from Java

2 Answers2

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