Question

当包含ViewPager的片段可见性设置为GONE或INVISIBLE时，ViewPager中的片段不会被初始化。如果父片段可见，它们似乎只是初始化。我怎样才能解决这个问题？我想要做的就是让ViewPager加载它的片段（不超过两个），即使父片段对于用户来说还不可见。

演示问题的示例项目：

MainActivity：

public class PagerFragment extends Fragment {

  ViewPager pager;
  @Override
  public View onCreateView(LayoutInflater inflater,
                           ViewGroup container,
                           Bundle savedInstanceState) {
    Log.d("PageFragment", "onCreateView");
    View result=inflater.inflate(R.layout.pager, container, false);
    pager=(ViewPager)result.findViewById(R.id.pager);
    pager.setAdapter(buildAdapter());
    return(result);
  }

  private PagerAdapter buildAdapter() {
    return(new SampleAdapter(getActivity(), getChildFragmentManager()));
  }
}

PagerFragment：

public class SampleAdapter extends FragmentPagerAdapter {
  Context ctxt=null;

  public SampleAdapter(Context ctxt, FragmentManager mgr) {
    super(mgr);

    this.ctxt=ctxt;

  }

  @Override
  public int getCount() {
    return(10);
  }

  @Override
  public Fragment getItem(int position) {
    Log.d("SampleAdapter","getItem");
    return(EditorFragment.newInstance(position));
  }

  @Override
  public String getPageTitle(int position) {
    return(EditorFragment.getTitle(ctxt, position));
  }
}

SampleAdapter：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:id="@+id/tabLayout">
        <FrameLayout
            android:id="@+id/startTab"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
        </FrameLayout>

        <FrameLayout
            android:id="@+id/editTab"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
        </FrameLayout>
    </FrameLayout>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/tabLayout"
        android:text="switch"
        android:id="@+id/switchButton"/>

</RelativeLayout>

main_layout：

public class StartFragment extends Fragment {

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d("StartFragment","onCreate");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View result=inflater.inflate(R.layout.start, container, false);
        Log.d("StartFragment","onCreateView");
        return(result);
    }
}

StartFragment：

public class EditorFragment extends Fragment {
  private static final String KEY_POSITION="position";

  static EditorFragment newInstance(int position) {
    EditorFragment frag=new EditorFragment();
    Bundle args=new Bundle();

    args.putInt(KEY_POSITION, position);
    frag.setArguments(args);

    return(frag);
  }

  static String getTitle(Context ctxt, int position) {
    return(String.format(ctxt.getString(R.string.hint), position + 1));
  }

  @Override
  public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d("EditorFragment","onCreate");
  }

  @Override
  public View onCreateView(LayoutInflater inflater,
                           ViewGroup container,
                           Bundle savedInstanceState) {
    View result=inflater.inflate(R.layout.editor, container, false);
    EditText editor=(EditText)result.findViewById(R.id.editor);
    int position=getArguments().getInt(KEY_POSITION, -1);

    editor.setHint(getTitle(getActivity(), position));
    Log.d("EditorFragment","onCreateView");
    return(result);
  }

  @Override
  public void onResume() {
    super.onResume();

  }
}

EditorFragment：

VK_FORMAT_R16_UINT

Answer 1

想出了解决问题的方法。我向viewpager添加了一个OnAttachStateChangeListener，然后调用setOffscreenPageLimit。这会在ViewPager中触发populate（），即使PagerFragment的可见性设置为GONE，它也会将所有片段添加到适配器。 setOffscreenPageLimit只能在视图附加到窗口后调用，否则populate（）将在适配器填充片段之前返回。

PagerFragment：

@Override
  public View onCreateView(LayoutInflater inflater,
                           ViewGroup container,
                           Bundle savedInstanceState) {
    View result=inflater.inflate(R.layout.pager, container, false);
    final ViewPager pager=(ViewPager)result.findViewById(R.id.pager);
    pager.setAdapter(buildAdapter());
    pager.addOnAttachStateChangeListener(new View.OnAttachStateChangeListener() {
      @Override
      public void onViewAttachedToWindow(View v) {
        pager.setOffscreenPageLimit(2);
      }

      @Override
      public void onViewDetachedFromWindow(View v) {

      }
    });
    return(result);
  }

当其父可见性设置为GONE / INVISIBLE时，为FragmentPagerAdapter初始化片段

1 个答案: