BottomNavigation 初始 setCurrentItem 不显示片段并且重新启动片段失败

Question

我有一个 Main Activity，它使用 TabSelectedListener 来显示 AHBottomNavigation 菜单的片段。名为 "FirstFragment" 的片段包含一个 FragmentPagerAdapter，它允许用户在两个选项卡之间滑动，每个选项卡都有自己的片段，称为 FirstTabInFirstFragmentFragment 和 SecondTabInFirstFragmentFragment（为简单起见重命名）。

我的问题是：

a).当主 Activity 启动时，"First" 底部导航菜单项被 select 编辑，但是 "FirstFragment" 未启动。因此，它显示了正确的项目 selected，但屏幕是空白的。如果我再次点击菜单项，它只会启动第一个片段。

b).一旦 FirstFragment 正确启动并显示在屏幕上（通过 a 中的临时修复），如果我 select 一个不同的菜单项（即导航到 SecondFragment）然后 select FirstFragment 的再次打开菜单项，其中的两个选项卡是空白的。此外，两个选项卡的片段之间的滑动不起作用并得到 "stuck"，因此您必须将其一直拉到一侧或一直拉到另一侧。

希望我已经清楚地解释了我的问题 - 如果有任何遗漏，我可以提供更多详细信息。
请注意，我使用的是 com.aurelhubert.ahbottomnavigation.AHBottomNavigation
以下是相关文件：

MainActivity.java:

public class MainActivity extends AppCompatActivity{

private AHBottomNavigationAdapter navigationAdapter;
private AHBottomNavigationViewPager viewPager;
private AHBottomNavigation bottomNavigation;

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

    // Add menu items to bar
    bottomNavigation = (AHBottomNavigation) findViewById(R.id.bottom_navigation);
    this.createNavItems();

    bottomNavigation.setOnTabSelectedListener(new AHBottomNavigation.OnTabSelectedListener() {
        @Override
        public boolean onTabSelected(int position, boolean wasSelected) {

            //show fragment
            if (position==0)
            {
                FirstFragment firstFragment=new FirstFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.content_id,firstFragment).commit();
            }else  if (position==1)
            {
                SecondFragment secondFragment=new SecondFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.content_id, secondFragment).commit();
            }else  if (position==2)
            {
                ThirdFragment thirdFragment=new ThirdFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.content_id,thirdFragment).commit();
            }else{
                FourthFragment fourthFragment=new FourthFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.content_id,fourthFragment).commit();
            }

            return true;
        }
    });
}

private void createNavItems(){
    navigationAdapter = new AHBottomNavigationAdapter(this, R.menu.navigation);
    navigationAdapter.setupWithBottomNavigation(bottomNavigation);

    // set current item
    bottomNavigation.setCurrentItem(0);
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/content_id"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <com.aurelhubert.ahbottomnavigation.AHBottomNavigation
        android:id="@+id/bottom_navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"/>

</android.support.design.widget.CoordinatorLayout>

FirstFragment.java:

public class FirstFragment extends Fragment {

    private FragmentActivity mContext;

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

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

    }

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

        // Set the content of the activity to use the activity_main.xml layout file
        //setContentView(R.layout.activity_first);

        // Find the view pager that will allow the user to swipe between fragments
        ViewPager viewPager = (ViewPager) getView().findViewById(R.id.viewpager);

        // Create an adapter that knows which fragment should be shown on each page
        // using getFragmentManager() will work too
        FirstFragmentPagerAdapter adapter = new FirstFragmentPagerAdapter(mContext.getSupportFragmentManager(), mContext);

        // Set the adapter onto the view pager
        viewPager.setAdapter(adapter);

        TabLayout tabLayout = (TabLayout) getView().findViewById(R.id.sliding_tabs);
        tabLayout.setupWithViewPager(viewPager);
    }

    /**
     * Override to set context.  This context is used for getSupportFragmentManager in onCreateView
     * @param activity
     */
    @Override
    public void onAttach(Activity activity) {
        mContext=(FragmentActivity) activity;
        super.onAttach(activity);
    }

}

fragment_first.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <android.support.design.widget.TabLayout
            android:id="@+id/sliding_tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabMode="fixed"
            app:tabBackground="@color/firstTabBackground"
            app:tabIndicatorColor="@color/firstTabIndicatorColor"/>

        <android.support.v4.view.ViewPager
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="0px"
            android:layout_weight="1"/>

    </LinearLayout>


</android.support.constraint.ConstraintLayout>

FirstFragmentPagerAdapter.java:

public class FirstFragmentPagerAdapter extends FragmentPagerAdapter {

    private Context context;

    public FirstFragmentPagerAdapter(FragmentManager fm, Context mContext){
        super(fm);
        context = mContext;
    }


    /**
     * The ViewPager asks the adapter for the fragment at a given position,
     * i.e. for the 1st fragment, the ViewPager asks for the fragment at
     * position 1.
     * @param position
     * @return
     */
    @Override
    public Fragment getItem(int position){
        if (position == 0){
            return new FirstTabInFirstFragmentFragment();
        }
        else{
            return new SecondTabInFirstFragmentFragment();
        }
    }

    /**
     * On launch, the ViewPager asks the adapter how many pages there will be.
     * Here, our adapter returns how many pages there will be.
     * @return
     */
    @Override
    public int getCount() {return 2;}

    @Override
    public CharSequence getPageTitle(int position) {

        switch(position){
            case 0:
                return context.getResources().getString(R.string.first_tab_in_first_fragment_page_title);
            case 1:
                return context.getResources().getString(R.string.second_tab_in_first_fragment_page_title);
            default:
                return null;
        }
    }
}

Answer 1

首先，为了在启动时初始加载第一个片段，您必须将第一个片段视图定义为主视图的默认视图activity。

其次，选择底部划分菜单时，您需要有一个framelayout来加载每个片段的视图。在这里，您只是替换了main activity的父级布局，这是一个错误的概念，我相信.

因此您需要创建一个子框架布局来为每个底部导航菜单项加载片段视图。

编辑：

我的布局包含底部导航，

<?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:id="@+id/content_home"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/app_bar_home"
android:keepScreenOn="false">
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/ll_toolbar_home_search">

    <android.support.v7.widget.Toolbar
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary">
        <LinearLayout
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="30dp"
            android:background="@drawable/btn_style_white"
            android:layout_marginRight="10dp">
            <ImageView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:src="@drawable/ic_search"/>
            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginLeft="10dp"
                android:text="Search 18000+ products"
                android:id="@+id/tv_search_home"/>
        </LinearLayout>

    </android.support.v7.widget.Toolbar>

</LinearLayout>


<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/ll_toolbar_home_search"
    android:layout_above="@+id/navigation"
    android:id="@+id/frame_layout_fragment"
    android:background="@color/white">
</FrameLayout>

<com.aurelhubert.ahbottomnavigation.AHBottomNavigation
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true" />

</RelativeLayout>

和 java class activity（仅包含底部导航操作的方法）如下：

private void BottomView1() {
    navigation = (AHBottomNavigation) findViewById(R.id.navigation);

    AHBottomNavigationItem item1 = new AHBottomNavigationItem("Home", R.drawable.ic_home, R.color.ash);
    AHBottomNavigationItem item2 = new AHBottomNavigationItem("Category", R.drawable.ic_category, R.color.ash);
    AHBottomNavigationItem item3 = new AHBottomNavigationItem("Search", R.drawable.ic_search, R.color.ash);
    AHBottomNavigationItem item4 = new AHBottomNavigationItem("Offers", R.drawable.ic_offers, R.color.ash);
    AHBottomNavigationItem item5 = new AHBottomNavigationItem("Cart", R.drawable.ic_cart, R.color.ash);

    navigation.addItem(item1);
    navigation.addItem(item2);
    navigation.addItem(item3);
    navigation.addItem(item4);
    navigation.addItem(item5);

    navigation.setCurrentItem(getResources().getColor(R.color.colorPrimaryDark));

    navigation.setTitleState(AHBottomNavigation.TitleState.ALWAYS_SHOW);

    setCartNotification();

    navigation.setAccentColor(getResources().getColor(R.color.colorPrimaryDark));

    navigation.setOnTabSelectedListener(new AHBottomNavigation.OnTabSelectedListener() {
        @Override
        public boolean onTabSelected(int position, boolean wasSelected) {
            Intent ii ;
            Fragment selectedFragment = null;
            if(position==0){
                selectedFragment = HomeFragment.newInstance();
                FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                transaction.replace(R.id.frame_layout_fragment, selectedFragment);
                transaction.commit();
            } else if(position==1){
                ii = new Intent(HomeActivity.this, ShopByCategoryActivity.class);
                startActivity(ii);
            } else if(position==2){
                ii = new Intent(HomeActivity.this, SearchActivity.class);
                startActivity(ii);
            } else if(position==3){
                ii = new Intent(HomeActivity.this, OffersActivity.class);
                startActivity(ii);
            } else if(position==4){
                ii = new Intent(HomeActivity.this, MyCartActivity.class);
                startActivity(ii);
            }
            return true;
        }
    });
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.frame_layout_fragment, HomeFragment.newInstance());
    transaction.commit();
}

Answer 2

我分两步解决了这个问题。首先，在我的 Main Activiy 方法 createNavItems 中，除了执行 bottomNavigation.setCurrentItem(0);，我还必须使用默认片段手动更新 CoordinatorLayout（其 ID content_id）：

getSupportFragmentManager().beginTransaction().replace(R.id.content_id, new FirstFragment()).commit();

接下来，为了解决 TabLayout 问题，我不得不更改这一行：

FirstFragmentPagerAdapter adapter = new FirstFragmentPagerAdapter(mContext.getSupportFragmentManager(), mContext);

到

FirstFragmentPagerAdapter adapter = new FirstFragmentPagerAdapter(getChildFragmentManager(), mContext);

原因是当使用 ViewPager 将 Fragment 嵌套在其他 Fragment 中时，getFragmentManager() 用于在 Fragment 中管理 Fragment，而 mContext.getSupportFragmentManager() 用于 Activity。

BottomNavigation 初始 setCurrentItem 不显示片段并且重新启动片段失败

BottomNavigation initial setCurrentItem not showing fragment and relaunching fragment fails

android

android-fragments

bottomnavigationview

android-bottomnav

android-bottom-nav-view