Android: How to use a Handler handleMessage and access the reference to the MainActivity

Question

I have a service which receives a command from the Internet and launches a background thread. This thread is passed a handler from the service (the service is bounded and passed the handler) and sends a message to the handler to take a picture. I'm stuck on the implementation of the handler.

static Handler handler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            //TODO: Handle different types of messages
            mCamera.takePicture(null, null, MainActivity.this);
        }
};

Questions:

• Does Handler need to be static? Without static, I get "This Handler class should be static or leaks might occur"
• Does mCamera need to be static? I've been told to make mCamera static, but why is this necessary? Is there a way to setup takePicture without making mCamera static?
• What's the proper way to pass the reference to MainActivity? Right now I get the error: "No enclosing instance of the type MainActivity is accessible in scope"

Answer 1

You can make a class (Activity/Service) implement Handler.Callback and create a new Handler for it via new Handler(this).

Answer 2

You can change your code as follows:

    static Handler handler = new Handler() {

            MainActivity mActivity;

            @Override
            public void handleMessage(Message msg) {
                //TODO: Handle different types of messages
                if(mActivity != null) {
                    mActivity.mCamera.takePicture(null, null, mActivity);
                }
            }
    };

    void MainActivity::onCreate(Bundle savedState) {
         ...
         handler.mActivity = this;
    }

    void MainActivity::onDestroy() {
        ...
        handler.mActivity = null;
    }