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

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，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;
    }
}

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);
    }
}

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();
    }
}

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);
    }
}

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;
    }
}

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;
    }
}

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();
        }
    }
}

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;
    }
}