依靠两个fragment之间共同依靠的activity实现通信

核心代码

//找到另外一个fragment的实例
 Fragment_2 f2= (Fragment_2) getActivity().getFragmentManager().findFragmentByTag("f2");
             
   f2.update("你好");

主函数在调用时增加tag参数

 FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.ll1,new Fragment_1(),"f1");
        fragmentTransaction.replace(R.id.ll2,new Fragment_2(),"f2");
        //☆☆☆☆☆☆
        fragmentTransaction.commit();