底部导航片段内有多个Tab片段 [英] Multiple Tab fragments inside bottom navigation fragment

问题描述

在底部导航中，具有三个选项卡(主页"，仪表板"，通知").每个底部导航选项卡都是一个片段.第一个标签，即.主页片段包含另一个顶部导航选项卡，该选项卡具有四个选项卡(选项卡1，选项卡2，选项卡3，选项卡4).

In bottom navigation with three tabs (Home, Dashboard, Notifications). Each bottom navigation tab is a fragment. The first tab ie. Home fragment contains another top navigation tabs having four tabs (Tab 1, Tab 2, Tab 3, Tab 4).

问题

1. 直接从主页标签导航到通知标签，然后返回主页标签，即Tab1/，之前选择过的标签标签(顶部导航标签)中的标签内容未加载.

1. When navigate from Home tab to Notifications tab directly and come back to Home tab, Tab1/which ever tab previously selected tab (top navigation tabs) the content of the tab is not loaded.

从 Tab 1 (首页片段"标签)滑动选项卡一直到 Notification (通知)选项卡并向后滑动，直到到达 Tab 4 选项卡的内容未加载，并且第一次从 Tab 4 滑动到 Tab 3 时，滑动不会进入 Tab 3 .选项卡指示器仅移动了一点，在第二次滑动时便按预期进入 Tab 3 .

When swipe the tabs from Tab 1 (Home fragment tab) all the way to Notification tab and swipe back, on reaching the Tab 4 the content of the tab is not loaded and on first swipe from Tab 4 to Tab 3 the swipe does not take to Tab 3. The tab indicator just move a little and on second swipe it goes to Tab 3 as expected.

该应用程序包含很多代码，因此我将整个代码链接到 Github .

The app contains a lot of code so I'll just link the full code to Github.

为快速参考，这里是我的代码

MainActivity.java

public class MainActivity extends AppCompatActivity {


    private ViewPager viewPager;

    NavigationView navigationView;

    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    viewPager.setCurrentItem(0);
                    return true;
                case R.id.navigation_dashboard:
                    viewPager.setCurrentItem(1);
                    return true;
                case R.id.navigation_notifications:
                    viewPager.setCurrentItem(2);
                    return true;
            }
            return false;
        }

    };

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

        // Hide the activity toolbar
        getSupportActionBar().hide();

        //Initializing viewPager
        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);


        final BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                switch (position){
                    case 0:
                        navigation.setSelectedItemId(R.id.navigation_home);
                        break;
                    case 1:
                        navigation.setSelectedItemId(R.id.navigation_dashboard);
                        break;
                    case 2:
                        navigation.setSelectedItemId(R.id.navigation_notifications);
                        break;
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });


    }

    private void setupViewPager(ViewPager viewPager) {
        BottomNavPagerAdapter adapter = new BottomNavPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new FirstFragment());
        adapter.addFragment(new SecondFragment());
        adapter.addFragment(new ThirdFragment());
        viewPager.setAdapter(adapter);
    }

}

FirstFragment.java(主页)

FirstFragment.java (Home)

public class FirstFragment extends Fragment {


    private TabLayout tabLayout;
    private ViewPager firstViewPager;

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


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

        View rootView = inflater.inflate(R.layout.fragment_first, container, false);

        firstViewPager = (ViewPager) rootView.findViewById(R.id.viewpager_content);

        tabLayout = (TabLayout) rootView.findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(firstViewPager);

        setupViewPager(firstViewPager);
        return rootView;
    }

    private void setupViewPager(ViewPager viewPager) {
        TabViewPagerAdapter adapter = new TabViewPagerAdapter(getActivity().getSupportFragmentManager());
        adapter.addFragment(new Tab1Fragment(), "Tab 1");
        adapter.addFragment(new Tab1Fragment(), "Tab 2");
        adapter.addFragment(new Tab1Fragment(), "Tab 3");
        adapter.addFragment(new Tab1Fragment(), "Tab 4");
        viewPager.setAdapter(adapter);
    }
}

问题

1. 代码有什么问题?
2. 如何解决此问题? (必须提供布局)，还是有更好的方法从屏幕截图中得出布局?

推荐答案

实际上，这是一个常见错误-您在片段内使用Activity的FragmentManager，但是由于该片段包含另一个 child 片段，您必须使用片段本身的FragmentManager.因此修复很简单-您只需在片段内将getActivity().getSupportFragmentManager()更改为getChildFragmentManager()，因此代码将为:

Actually, it is a common mistake - you're using FragmentManager of your Activity inside the fragment, but since this fragment contains another child fragments you have to use FragmentManager of the fragment itself. So the fix is simple - you just have to change getActivity().getSupportFragmentManager() to getChildFragmentManager() inside your fragments, so the code will be:

private void setupViewPager(ViewPager viewPager) {
    TabViewPagerAdapter adapter = new TabViewPagerAdapter(getChildFragmentManager());
    ...
    ...
    viewPager.setAdapter(adapter);
}

这应该可以正常工作.

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