How can a message be acquired in the main thread using Handler and Looper?

In Android, the Looper class is primarily used to process messages in the main (UI) thread, creating a message processing loop, and the Handler class places messages into this Looper's queue.

To receive messages in the main thread:

1. Call Looper.getMainLooper() in the main thread, which returns the main thread's Looper.
2. Create a Handler associated with this Looper:

Handler handler = new Handler(Looper.getMainLooper()) {
    @Override
    public void handleMessage(Message msg) {
        // Handle message in the main thread
    }
};

3. Messages or Runnable objects can be sent to this Handler, and they will be processed in the main thread.

Thus, Handler and Looper provide a message queue and processing mechanism in the main thread, allowing safe UI updates from other threads.