handler优化

//弱引用的使用
 private static class SwitchHandler extends Handler {
        private WeakReference<SplashActivity> mWeakReference;

        SwitchHandler(SplashActivity activity) {
            mWeakReference = new WeakReference<SplashActivity>(activity);
        }

        @Override
        public void handleMessage(Message msg) {
            SplashActivity activity = mWeakReference.get();
            if (activity != null) {
                WeatherActivity.launch(activity);
                activity.finish();
            }
        }
    }