Passing callback from JavaScript to Java (Android)

I'm developing an app for Android using HTML5/JavaScript. Running into limitations, I want to call a function that is realized in the Java code from within JavaScript. To be more precise, I want to create a certain type of dialog. This is fairly easy (I will only give a rough outline/stub):

public class MyClass () {
    // other stuff

    public void createMyDialog (/* arguments */) {
        DialogBuilder builder = ...
        builder.setItems(myItems, new DialogInterface.OnClickListener () {
            @Override
            public void OnClick (DialogInterface dialog, int which) {
                droidGap.loadUrl(/* what now? */);
            }
        });
    }
}

Then this class is revealed to JavaScript with

MyClass myClass = new MyClass();
appView.addJavascriptInterface(myClass, "myClass");

So far so good. I can now access window.myClass.createMyDialog() from within JavaScript. However, what I'd like to do is pass a callback that will be called with the which variable as a parameter. This means having a signature like

public void createMyDialog (final String callback)

and calling it with something like

window.myClass.createMyDialog(
    function (which) {
        alert(which);
    }
);

I can get this to work my passing the function as a string (using String() around the function) and calling appView.loadUrl("javascript:(" + callback + ")(" + which + ");"); from Java. Never mind that this solution doesn't feel very clean, it has a big disadvantage – to finally come to the point. Because in JavaScript, I'm actually calling createMyDialog from within a class and I'd like to do somehting like this:

function myJSClass () {
    this.myVar = -1;

    this.myFunc = function () {
        window.myClass.createMyDialog(
            function (which) {
                this.myVar = which;
            }
        );
    }
}

var myObj = new myJSClass();
myObj.myFunc();

The problem now being that with the solution from above, this will refer to window rather than the class instance. This isn't a new problem, but none of the typical solutions (storing var _this = this outside the call and using _this.myVar = which or using bind) work as the context of this is just completely lost because the function will be called from Java.

I know that it has to be possible since the PhoneGap framework offers navigator.notification.confirm which pretty much does exactly what I want. What is the way to go here?

Thanks in advance!