Looper

A Looper (opens new window) is an Android class used to run a message loop for a thread, which usually do not have one associated with them.

The most common Looper in Android is the main-loop, also commonly known as the main-thread. This instance is unique for an application and can be accessed statically with Looper.getMainLooper().

If a Looper is associated with the current thread, it can be retrieved with Looper.myLooper().

Create a simple LooperThread

A typical example of the implementation of a Looper thread given by the official documentation uses Looper.prepare() and Looper.loop() and associates a Handler with the loop between these calls.

class LooperThread extends Thread {
    public Handler mHandler;

    public void run() {
        Looper.prepare();

        mHandler = new Handler() {
            public void handleMessage(Message msg) {
                // process incoming messages here
            }
        };

        Looper.loop();
    }
}

Run a loop with a HandlerThread

A HandlerThread (opens new window) can be used to start a thread with a Looper. This looper then can be used to create a Handler for communications with it.

HandlerThread thread = new HandlerThread("thread-name");
thread.start();
Handler handler = new Handler(thread.getLooper());