从父片段到选项卡片段的接口侦听器不起作用

Question

我正在尝试为标签片段的父片段实现接口侦听器。它给出 Null 值错误。 这是我的代码。 在下面给出的代码中，我创建了名为 OnFeedItemClickListener 的接口，并尝试将该方法覆盖到选项卡片段中。

parent_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    android:id="@+id/drawer_layout"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    app:layout_scrollFlags="scroll|enterAlways"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical">

    <!-- TODO: Update blank fragment layout -->
    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/AppTheme.PopupOverlay" />
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="bottom|end"
            app:layout_collapseMode="parallax"
            app:layout_scrollFlags="scroll|enterAlways"
            android:orientation="horizontal">


            <Button
                android:id="@+id/ButtonId"
                style="@style/Widget.AppCompat.Button.Borderless"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="Switch"
                android:textAllCaps="false"
                android:textColor="#FFFFFF" />

        </LinearLayout>
        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/colorPrimary"
            app:tabGravity="fill"
            app:tabMode="fixed"/>


        </android.support.design.widget.AppBarLayout>
    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_scrollFlags="scroll|enterAlways"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />


</android.support.design.widget.CoordinatorLayout>
    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/activity_main_drawer" >
    </android.support.design.widget.NavigationView>
</android.support.v4.widget.DrawerLayout>

fragment_one.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FFFFFF">


    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:layout_above="@+id/navigation" />

</RelativeLayout>

ParentFragment.java

public class ParentFragment extends Fragment implements NavigationView.OnNavigationItemSelectedListener {

    private List<Fragment> fragmentList = new ArrayList<>();
    private List<String> titleList = new ArrayList<>();
    private View rootView;
    private ViewPager viewPager;
   private TextTabsAdapter adapter;
    private TabLayout tabLayout;
    private Button BtnId;


    private OnFeedItemClickListener onFeedItemClickListener;

    public ParentFragment() {
        // Required empty public constructor
    }




    private void initialise() {
        Toolbar toolbar = (Toolbar) rootView.findViewById(R.id.toolbar);
        toolbar.setTitle("Dashboard");
        DrawerLayout drawer = (DrawerLayout) rootView.findViewById(R.id.drawer_layout);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                getActivity(), drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        drawer.setBackgroundColor(getResources().getColor(R.color.whiteColor));
        toggle.syncState();

        NavigationView navigationView = (NavigationView) rootView.findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        viewPager = (ViewPager) rootView.findViewById(R.id.viewPager);
        tabLayout = (TabLayout) rootView.findViewById(R.id.tabs);
    }
    private void prepareDataResource() {

            addData(new FragmentOne(), "ONE");
            addData(new FragmentTwo(), "TWO");

    }


    private void addData(Fragment fragment, String title) {
        fragmentList.add(fragment);
        titleList.add(title);
    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        rootView = inflater.inflate(R.layout.parent_fragment, container, false);

        initialise();
        prepareDataResource();

        adapter = new TextTabsAdapter(getChildFragmentManager(), fragmentList, titleList);

        // Bind Adapter to ViewPager.
        viewPager.setAdapter(adapter);

        // Link ViewPager and TabLayout
        tabLayout.setupWithViewPager(viewPager);
        BtnId = (Button) rootView.findViewById(R.id.CountryId);

        BtnId.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                onFeedItemClickListener.onButtonClick();
            }
        });
        return rootView;
    }


    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        return false;
    }




    public void setOnFeedItemClickListener(OnFeedItemClickListener onFeedItemClickListener) {
        this.onFeedItemClickListener = onFeedItemClickListener;
    }


    public interface OnFeedItemClickListener {
        void onButtonClick();


    }
}

FragmentOne.java

public class FragmentOne extends Fragment implements FeedsAdapter.OnFeedItemClickListener,ParentFragment.OnFeedItemClickListener{


    private RecyclerView mrecyclerview;
    private FeedsAdapter feedadapter;
    View rootView;


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        rootView =  inflater.inflate(R.layout.fragment_one, container, false);
        mrecyclerview = (RecyclerView) rootView.findViewById(R.id.recyclerView);
        mrecyclerview.setLayoutManager(new LinearLayoutManager(getContext()));


        populateFeedsData();
        ParentFragment parentFragment = new ParentFragment();
        parentFragment.setOnFeedItemClickListener(this);

        return rootView;
    }


    @Override
    public void onButtonClick() {
        Toast.makeText(getContext(), "ButtonClicked", Toast.LENGTH_SHORT).show();
    }
}

请帮我解决这个问题，非常感谢:)

Answer 1

在您的 FragmentOne 类中，您正在创建 ParentFragment 的新实例。

ParentFragment parentFragment = new ParentFragment();

您实际需要做的是获取创建 FragmentOne 子片段的 ParentFragment 实例。

要做到这一点，你可以试试这个：

ParentFragment parentFrag = ((ParentFragment)FragmentOne.this.getParentFragment());

现在你可以通过parentFrag调用setOnFeedItemClickListener()函数了。

希望对你有帮助！