Android：ViewPager仅显示第一个片段，其他页面为空白

Question

我有一个ViewPager，它将一系列FoodItem显示为片段。 那部分工作正常。

现在，我希望具有一个功能，以便用户单击按钮时，他们可以查看有关该FoodItem的更多信息。

为此，我想用另一个片段替换单击的片段。 我在这里修改了此代码以适合我的目的。 它有效-当我单击按钮时，它将替换该特定片段。 但它仅显示并适用于一个片段。 其他片段完全空白。

这是我的适配器和片段：

public class SectionsPagerAdapter extends FragmentStatePagerAdapter {
private ArrayList<FoodItem> items;

public SectionsPagerAdapter(FragmentManager fm, ArrayList<FoodItem> items) {
    super(fm);
    this.items = items;
}

@Override
public Fragment getItem(int position) {
    System.out.println("PRINT: POS " + position);
    RootFragment f = new RootFragment();
    return f.newInstance(position);


}

@Override
public int getCount() {
    return items.size();
}


public class PlaceholderFragment extends Fragment{

    private final String ARG_SECTION_NUMBER = "section_number";


    public PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        System.out.println("PRINT: INSTANCE" + sectionNumber);
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_card_layout, container, false);
        singleItem = items.get(getArguments().getInt(ARG_SECTION_NUMBER));

        // populate views here

        //Below is the button for replacing the Fragment with another Fragment.

        Button testMore = (Button) view.findViewById(R.id.testMore);
        testMore.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction trans = getFragmentManager()
                        .beginTransaction();
                                trans.replace(R.id.root_frame, new MoreInfoFragment().newInstance(getArguments().
                        getInt(ARG_SECTION_NUMBER)));
                trans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
                trans.addToBackStack(null);

                trans.commit();
            }
        });

        return view;
    }

}

public class MoreInfoFragment extends Fragment {

    private final String ARG_SECTION_NUMBER = "section_number";


    public MoreInfoFragment newInstance(int sectionNumber) {
        MoreInfoFragment fragment = new MoreInfoFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public MoreInfoFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.more_info_layout, container, false);
        singleItem = items.get(getArguments().getInt(ARG_SECTION_NUMBER));

        //populate views here

        return view;

    }
}

public class RootFragment extends Fragment {

    private static final String TAG = "RootFragment";
    private final String ARG_SECTION_NUMBER = "section_number";

    public RootFragment newInstance(int sectionNumber) {
        RootFragment fragment = new RootFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
       View view = inflater.inflate(R.layout.root_fragment, container, false);

       FragmentTransaction transaction = getFragmentManager()
                .beginTransaction();

      transaction.replace(R.id.root_frame, new PlaceholderFragment().newInstance(getArguments().
        getInt(ARG_SECTION_NUMBER)));

        System.out.println("PRINT: ROOT" + getArguments().getInt(ARG_SECTION_NUMBER));


        transaction.commit();

        return view;
    }

}
}

这是我的主要活动：

private ViewPager mViewPager;
private static ArrayList<FoodItem> sample;
private PagerContainer mContainer;


public CardLayout(){

}


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.getWindow().addFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND);
    setContentView(R.layout.activity_card_layout);

   //Sample array
    sample = new ArrayList<>();
    sample.add(new FoodItem("French Fries", "Super delicious and crispy!"))
    sample.add(new FoodItem("Burger", "Made with real Krabby Patty"))
    sample.add(new FoodItem("Pickles", "So green")) // This is the only one that displays

   //PagerContainer is a FrameLayout that has a ViewPager as a child. 
   //I want my ViewPager to display edges of the previous and next part so    
   //PagerContainer is used for that purpose.
    mContainer = (PagerContainer) findViewById(R.id.pager_container);

    mViewPager = (ViewPager) findViewById(R.id.viewPager);

   // This is to adjust the viewpager according to size of screen 
    mContainer.getViewTreeObserver().
            addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
                @SuppressLint("NewApi")
                @SuppressWarnings("deprecation")
                @Override
                public void onGlobalLayout() {
                    height = mContainer.getHeight();

                    double heightSize =  height * 0.8;
                    height = (int) heightSize;
                    double widthSize = height*0.6;
                    width = (int) widthSize;


                    mViewPager.setLayoutParams(new FrameLayout.LayoutParams(width, height, Gravity.CENTER));
                    mViewPager.setPageMargin(width /30);


                    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN)
                        mContainer.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                    else
                        mContainer.getViewTreeObserver().removeGlobalOnLayoutListener(this);
                }
            });

    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager(), sample);
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setAdapter(mSectionsPagerAdapter);
    mViewPager.setOffscreenPageLimit(mSectionsPagerAdapter.getCount());


    mViewPager.setClipChildren(false);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            finish();
        }
    });

}

哦，正在显示的Fragment甚至不是我ArrayList中的第一个！ 这是最后一次。

我觉得自己似乎遗漏了一些明显的东西，但是我已经看了十遍这段代码，但仍然找不到阻止其他页面显示的原因。

例如，这是首页的外观：

如果我滑到第二页，那是全白的（我的root_fragment背景色）

这适用于之后的每个片段。

你们有什么想法/建议吗？

Answer 1

覆盖SelectionsPageAdapter中的方法getItem（）

 @Override
    public Fragment getItem(int position) {
        // if the position is 0 we are returning the First tab
        if (position == 0) 
        {
            Fragment tab1 = new PlaceholderFragment ();
            return tab1;

        } else if (position == 1)           
        {
            Fragment tab2 = new MoreInfoFragment ();
            return tab2;

        } else if (position == 2) {

            Fragment tab3 = new RootFragment ();
            return tab3;

        } 

    }