每日一道面试题（第2期）---Activity 与 Fragment 之间常见的几种通信方式？

超、凢脫俗 2022-01-20 10:13 175阅读 0赞

> 零零碎碎的东西总是记不长久，仅仅学习别人的文章也只是他人咀嚼后留下的残渣。无意中发现了这个[每日一道面试题][Link 1]，想了想如果只是简单地去思考，那么不仅会收效甚微，甚至难一点的题目自己可能都懒得去想，坚持不下来。所以不如把每一次的思考、理解以及别人的见解记录下来。不仅加深自己的理解，更要激励自己坚持下去。

# 参数传递 #

如果是在建立Fragment时需要Activity中的一些数据作为初始化，那么可以通过Activity中的setArguments(bundle)方法传递参数，在Fragment中通过getArguments获得Bundle对象来解析参数。

public class MainActivity extends BaseActivity {
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_register);
    
            Fragment firstFragment = new FirstFragment();
            Bundle bundle = new Bundle();
            bundle.putString("data", "数据");
            
            //显示Fragment
            FragmentManager manager = getFragmentManager();
            FragmentTransaction transaction = manager.beginTransaction();
            transaction.add(R.id.fragment, firstFragment).show(firstFragment).commit();
        }
    }
    public class FirstFragment extends Fragment {
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            View view = inflater.inflate(R.layout.fragment_first, container, false);
            Bundle bundle = getArguments();
            String data = bundle.getString("data");
            return view;
        }
    }
    复制代码

# 数据传递、事件监听 #

如果是创建后需要进行通信，那可以通过接口回调、广播、eventbus来进行。这些都可以是双向的，只是看你怎么设置。以下例子皆监听Fragment中的事件。

### 接口回调 ###

在Fragment中

public class FirstFragment extends Fragment {
        private OnFragmentInteractionListener mListener;
        private Button button;
    
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            View view = inflater.inflate(R.layout.fragment_first, container, false);
            button = view.findViewById(R.id.bt_fragment);
            button.setOnClickListener(v -> mListener.onFragmentInteraction("接口发送消息啦"));
    
            return view;
        }
        @Override
        public void onAttach(Context context) {
            super.onAttach(context);
            //绑定Activity
            if (context instanceof OnFragmentInteractionListener) {
                mListener = (OnFragmentInteractionListener) context;
            } else {
                throw new RuntimeException(context.toString()
                        + " must implement OnFragmentInteractionListener");
            }
        }
        //解绑activity时设为null
        @Override
        public void onDetach() {
            super.onDetach();
            mListener = null;
        
        //自定义一个接口
        public interface OnFragmentInteractionListener {
            void onFragmentInteraction(String str);
        }
    }
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在Activity中实现OnFragmentInteractionListener接口重写onFragmentInteraction方法就可以了

public class MainActivity extends BaseActivity implements FirstFragment.OnFragmentInteractionListener {
        @Override
        public void onFragmentInteraction(String str) {
            Toast.makeText(this, "接口收到通知啦", Toast.LENGTH_SHORT).show();
        }
    }
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### 广播 ###

在Activity中注册广播

public class MainActivity extends BaseActivity implements FirstFragment.OnFragmentInteractionListener {
        //处理事件
        private BroadcastReceiver receiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();
                switch (action){
                    case BROADCAST_ACTION:
                        Toast.makeText(context, "收到通知啦", Toast.LENGTH_SHORT).show();
                        break;
                }
            }
        };
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_register);
            //注册广播
            IntentFilter filter = new IntentFilter();
            filter.addAction("com.goldenhamster.myboradcastreceiver");
            registerReceiver(receiver, filter);
        }
    
        @Override
        protected void onDestroy() {
            super.onDestroy();
            //记得取消注册
            unregisterReceiver(receiver);
        }
    }
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在Fragment中发送广播

public class FirstFragment extends Fragment {
    
        private Button button;
        
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            View view = inflater.inflate(R.layout.fragment_first, container, false);
            button = view.findViewById(R.id.bt_fragment);
            button.setOnClickListener(v -> getActivity().sendBroadcast(new Intent("com.goldenhamster.myboradcastreceiver")));
            return view;
        }
    }
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### EventBus框架 ###

设置信息类

public class EventUtil {
        private String mes;
        public EventUtil(String mes){
            this.mes = mes;
        }
        public String getMes() {
            return mes;
        }
    }
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在Activity中注册监听EventBus

public class MainActivity extends BaseActivity{
        @Override
        public void onStart() {
            super.onStart();
            EventBus.getDefault().register(this);
        }
        @Override
        public void onStop() {
            super.onStop();
            EventBus.getDefault().unregister(this);
        }
        //使用注解标记事件处理方法
        @Subscribe
        public void onEvent(EventUtil event){
            if(event.getMes().equals("data")){
                Toast.makeText(context, "收到通知啦", Toast.LENGTH_SHORT).show();
            }
        }
    }
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在Fragment中发送消息

public class FirstFragment extends Fragment {
        private Button button;
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            View view = inflater.inflate(R.layout.fragment_first, container, false);
            button = view.findViewById(R.id.bt_fragment);
            button.setOnClickListener(v -> EventBus.getDefault().post(new EventUtil("data")));
            return view;
        }
    }
    复制代码

[Link 1]: https://link.juejin.im?target=https%3A%2F%2Fgithub.com%2FMoosphan%2FAndroid-Daily-Interview