handlerThread example

HandlerThread.java

// start action when thread start
HandlerThread handlerThread = new HandlerThread("printingThread") {
    @Override
    protected void onLooperPrepared() {
        super.onLooperPrepared();
        // TODO: my action
    }
};
handlerThread.start();  // this will trigger onLooperPrepared

// thread communications using handler
// 1. In UI thread, send message to background thread with background thread's handler 
// send message from ui thread to background thread 
HandlerThread handlerThread = new HandlerThread("myThread");
handlerThread.start();
Handler handler = new Handler(handlerThread.getLooper()) {
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        Bundle bundle = msg.getData();
        String value1 = bundle.getString("key1");
        String value2 = bundle.getString("key2");
        //TODO: my action

    }
};
Message message = new Message();    // or handler.obtainMessage();
Bundle bundle = new Bundle();
bundle.putString("key1", "value1");
bundle.putString("key2", "value2");
message.setData(bundle);
handler.sendMessage(message);       // or handler.sendMessageDelayed(message, 1000);

// 2. In background thread, send message to UI thread with UI thread's handler 
final Handler uiHandler = new Handler(Looper.getMainLooper()) {
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        Bundle bundle = msg.getData();
        boolean printComplete = bundle.getBoolean("printComplete", false);
        if (!printComplete) {
            Toast.makeText(getBaseContext(), "Printing receipt failed, please check bluetooth printer setup!", Toast.LENGTH_LONG).show();
        }
    }
};

HandlerThread handlerThread = new HandlerThread("printingThread") {
    @Override
    protected void onLooperPrepared() {
        super.onLooperPrepared();
        // TODO: my action
        
        // send message back to ui thread after action completed
        Message msg = new Message();
        Bundle b = new Bundle();
        b.putBoolean("printComplete", printComplete);
        msg.setData(b);
        uiHandler.sendMessage(msg);
    }
};
handlerThread.start();  // this will trigger onLooperPrepared