android - 调用 Fragment 清除 startActivity() 上的应用程序视图

Question

我是 Android 开发的新手，并且在导航菜单中添加了一个附加项目，该菜单成功打开了外部浏览器窗口，但startActivity在onActivityCreated执行时会清除应用程序屏幕（导航菜单除外）。

尽管为此工作了几天，但我没有取得任何进展，所以我现在寻求帮助。对于有更多经验的人来说，这可能是一个简单的问题。我花了一周时间查看 SO、YouTube 和 Google Developer Courses 中的所有其他答案，试图解决这个问题，所以我现在寻求帮助。

网站片段.java

public class WebsiteFragment extends Fragment {
    View myFragment;

    RecyclerView websiteList;
    LinearLayoutManager layoutManager;

    private static final String COMMON_TAG="CombinedLifeCycle";
    private static final String ACTIVITY_NAME =WebsiteFragment.class.getSimpleName();
    private static final String TAG=ACTIVITY_NAME;

    public static WebsiteFragment newInstance() {
        WebsiteFragment websiteFragment = new WebsiteFragment();
        return websiteFragment;    
    }

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

        Log.i(TAG,ACTIVITY_NAME+" onCreateView");

        websiteList = (RecyclerView)view.findViewById(R.id.websiteList);
        layoutManager = new LinearLayoutManager(getActivity());
        websiteList.setHasFixedSize(true);

        return view;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        Intent i = new Intent(Intent.ACTION_VIEW);
        i.setData(Uri.parse("https://english-alps.com"));
        // App Window is cleared??
        getActivity().startActivity(i);
        Log.i(TAG,ACTIVITY_NAME+" onActivityCreated");    
    }
}

fragment_webiste.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".WebsiteFragment">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/websiteList"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </androidx.recyclerview.widget.RecyclerView>

</FrameLayout>

编辑 21-08-2018

添加了以下代码以尝试保存Fragment状态，但它会生成错误：

java.lang.NullPointerException：尝试从空对象引用的字段“int androidx.fragment.app.Fragment.mIndex”中读取。

我的参数有问题getFragmentManager。变量应该如何getFragmentManager初始化？

public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState!=null){
        Log.i(TAG,ACTIVITY_NAME+" calling onSaveInstanceState");
        onSaveInstanceState(savedInstanceState);
    }
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    getFragmentManager().putFragment(outState,TAG,myFragment);
    Log.i(TAG,ACTIVITY_NAME+" onSaveInstanceState");
}

编辑#2 21-08-2018

Home.Java添加WebsiteFragment到 Activity

public class Home extends AppCompatActivity {

    BottomNavigationView bottomNavigationView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);

        bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);

        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                Fragment selectedFragment = null;
                switch (menuItem.getItemId()) {
                    case R.id.action_category:
                        selectedFragment = CategoryFragment.newInstance();
                        break;
                    case R.id.action_ranking:
                        selectedFragment = RankingFragment.newInstance();
                        break;
                    case R.id.action_website:
                        selectedFragment = WebsiteFragment.newInstance();
                        break;
                }
                FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                transaction.replace(R.id.frame_layout, selectedFragment);
                transaction.addToBackStack(String.valueOf(R.id.frame_layout)); /* 21.08.2018 */
                transaction.commit();
                return true;
            }

        });
        setDefaultKeyMode();

    }
}

编辑 #3 21-08-2018 activity_home.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Home">

    <FrameLayout
        android:id="@+id/frame_layout"
        android:animateLayoutChanges="true"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@+id/navigation"></FrameLayout>

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:background="@color/colorPrimary"
        app:itemIconTint="@drawable/nav_item_color_state"
        app:itemTextColor="@drawable/nav_item_color_state"
        app:menu="@menu/bottom_menu"
    />
</RelativeLayout>  

标签： androidandroid-fragments