android - fragment 在 ViewPager 中不可见

Question

我有一个 ViewPager，我想将 fragment 添加到其中。 可以在屏幕上正确查看 ViewPager，但遗憾的是它不包含任何内容。

我在一些posts中看到了建议替换

getSupportFragmentManager() 

与

getChildFragmentManager()

但我需要ActionBar。不幸的是，ChildFragmentmanager 在 AppCompatActivity 中不可用。

在调试时，我意识到调用了 Fragment 的 onCreateView() 方法并返回了一个布局。

问题如何让Fragments可见？我的代码与 sample 的主要区别在于？

Activity :

public class ViewPagerActivity extends AppCompatActivity {

    private ViewPager mViewPager;

    private List<Location> locationList = new ArrayList<>();
    private locationsBaseHandler db;
    private CustomPagerAdapter mAdapter;

    private Location mLocation;

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

        setContentView(R.layout.activity_viewpager);

        locationList.add(someData);

        mViewPager = (ViewPager) findViewById(R.id.viewpager);
        mAdapter  = new CustomPagerAdapter(this, getSupportFragmentManager(), locationList);

        mViewPager.setAdapter(mAdapter);

    }

}

寻呼机适配器:

public class CustomPagerAdapter extends FragmentPagerAdapter {

    private Context mContext;
    private List<Location> locationList = new ArrayList<>();

    public CustomPagerAdapter(Context mContext, FragmentManager fm, List<Location> locationList) {
        super(fm);

        this.locationList.addAll(locationList);
        this.mContext = mContext;
    }

    @Override
    public Fragment getItem(int position) {
        return LocationFragment.newInstance(position);
    }

    @Override
    public int getCount() {
        return 5;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return false;
    }
}

fragment :

public class LocationFragment extends Fragment {
    private static final String ARG_LAYOUT_ID = "page_number";

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

        return layout;
    }

    public static LocationFragment newInstance(int selectedIdForIndex) {
        LocationFragment fragment = new LocationFragment();

        Bundle args = new Bundle();
        args.putInt(ARG_LAYOUT_ID, selectedIdForIndex);
        fragment.setArguments(args);

        return fragment;
    }

    public int getPageNumber() {
        return getArguments().getInt(ARG_LAYOUT_ID);
    }
}

Answer 1

尝试移除 CustomPagerAdapter 中的方法 isViewFromObject。

@Override
public boolean isViewFromObject(View view, Object object) {
    return false;
}

我们可以看到对 isViewFromObject 的注释:

Determines whether a page View is associated with a specific key object as returned by {@link #instantiateItem(ViewGroup, int)}. This method is required for a PagerAdapter to function properly.