public void registerDisplayListener(DisplayListener listener, Handler handler) {
    if (listener == null) {
        throw new IllegalArgumentException("listener must not be null");
    }

    synchronized (mLock) {
        int index = findDisplayListenerLocked(listener);
        if (index < 0) {
            mDisplayListeners.add(new DisplayListenerDelegate(listener, handler));
            registerCallbackIfNeededLocked();
        }
    }
}
 

public void unregisterDisplayListener(DisplayListener listener) {
    if (listener == null) {
        throw new IllegalArgumentException("listener must not be null");
    }

    synchronized (mLock) {
        int index = findDisplayListenerLocked(listener);
        if (index >= 0) {
            DisplayListenerDelegate d = mDisplayListeners.get(index);
            d.clearEvents();
            mDisplayListeners.remove(index);
        }
    }
}
 

private int findDisplayListenerLocked(DisplayListener listener) {
    final int numListeners = mDisplayListeners.size();
    for (int i = 0; i < numListeners; i++) {
        if (mDisplayListeners.get(i).mListener == listener) {
            return i;
        }
    }
    return -1;
}
 

public DisplayListenerDelegate(DisplayListener listener, Handler handler) {
    super(handler != null ? handler.getLooper() : Looper.myLooper(), null, true /*async*/);
    mListener = listener;
}