Android Handler

    private final UIHandler uiHandler = new UIHandler(this);

    static class UIHandler extends Handler {
        private final WeakReference<DashboardFragment> mFragment;
        private static final int MSG_SHOW_MASK = 1;
        private static final int MSG_HIDE_MASK = 2;

        private UIHandler(DashboardFragment fragment) {
            mFragment = new WeakReference<>(fragment);
        }

        @Override
        public void handleMessage(Message msg) {
            if (mFragment.get() == null) {
                return;
            }
            DashboardFragment fragment = mFragment.get();
            switch (msg.what) {
                case MSG_SHOW_MASK:
                    fragment.mMask.setVisibility(View.VISIBLE);
                    break;
                case MSG_HIDE_MASK:
                    fragment.mMask.setVisibility(View.GONE);
                    break;
                default:
                    break;
            }
        }
    }
    
    @Override
    public void onDestroy() {
        super.onDestroy();
        uiHandler.removeCallbacksAndMessages(null);
    }