在activity中使用handler，ide会显示一个警告
This Handler class should be static or leaks might occur
意思是handler应用static修饰否则容易发生内存泄漏
我们又不能将handler声明成static然后将所有的成员变量都变成final，所以我们可以在activity创建一个匿名的handler， 然后让这个handler持有activity的若引用即可

   class DemoHandler<T> extends Handler
    {
        private WeakReference<T> mActivity;
 
        public DemoHandler(T activity)
        {
            mActivity = new WeakReference<>(activity);
        }
 
        @Override
        public void handleMessage(Message msg)
        {
            T activity = mActivity.get();
            super.handleMessage(msg);
 
            switch (msg.what)
            {
                case 0:
                    activity.getClass().getName();
                    LogUtils.i("send in static handel");
                    break;
            }
        }
    }