fragment+接口回调

//activity_main
<fragment
    android:id="@+id/left_fg"
    android:name="org.mobiletrain.a7_4fragment.LeftFragment"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="1"/>

<LinearLayout
    android:id="@+id/right_fg"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="2"
    android:orientation="vertical"/>
    
//left_layout
<ListView
    android:id="@+id/lv"
    android:layout_width="match_parent"
    android:layout_height="match_parent"></ListView>    
    
//right_layout
<TextView
    android:id="@+id/content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

public class LeftFragment extends Fragment {

    private List<String> list;
    //1.创建接口
    public interface UpdateRightFg {
        public void updateRightFg(String fileName);
    }
    //2.声明接口变量
    private UpdateRightFg updateRightFg;

    //3.实例化接口变量,该方法在Activity和Fragment产生关联时调用
    //参数Activity指Fragment的宿主Activity
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        if (activity instanceof UpdateRightFg) {
            updateRightFg = (UpdateRightFg) activity;
        }
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.left_layout, null);
        ListView listView = (ListView) view.findViewById(R.id.lv);
        initData();
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, list);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            //4.调用接口中的方法
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (updateRightFg != null) {
                    updateRightFg.updateRightFg(list.get(position));
                }
            }
        });
        return view;
    }

    private void initData() {
        list = new ArrayList<>();
        list.add("day1.txt");
        list.add("day2.txt");
        list.add("day3.txt");
        list.add("day4.txt");
    }

    
}

//5.在Activity中实现接口
public class MainActivity extends AppCompatActivity implements LeftFragment.UpdateRightFg {

    private RightFragment rightFg;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        rightFg = new RightFragment();
        transaction.replace(R.id.right_fg, rightFg).commit();
    }

    @Override
    public void updateRightFg(String fileName) {
        rightFg.updateTextView(fileName);
    }
}

public class RightFragment extends Fragment {

    private TextView content;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.right_layout, null);
        content = (TextView) view.findViewById(R.id.content);
        return view;
    }

    public void updateTextView(String fileName) {
        content.setText(getStringFromAssets(fileName));
    }

    /**
     * 根据文件名从资产文件夹中读取文件内容
     *
     * @param fileName 文件名
     * @return
     */
    public String getStringFromAssets(String fileName) {
        //获得资产文件夹管理器
        AssetManager assets = getActivity().getAssets();
        StringBuffer result = new StringBuffer();
        InputStream is = null;
        try {
            //通过IO流读取资产文件中的内容
            is = assets.open(fileName);
            int len;
            byte[] buf = new byte[1024];
            while ((len = is.read(buf)) != -1) {
                result.append(new String(buf, 0, len));
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null)
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
        return result.toString();
    }
}