android - ViewPager + Fragments - 未显示 fragment

Question

我正在尝试使用 viewpager 来显示多个 fragment 。目前我只有一个 fragment ，但它似乎从未被实例化。我尝试使用 pager.setCurrentItem(0) 但从未调用适配器中的 getItem 方法。有谁知道为什么我的 fragment 没有加载到下面的代码中？

主要 Activity

public class MainActivity extends SherlockFragmentActivity {

MyPagerAdapter adapter;

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

    // Create the FragmentPager Adapter and assign it to the viewpager
    adapter = new MyPagerAdapter( getSupportFragmentManager(), this );
    ViewPager pager = ( ViewPager ) findViewById( R.id.pager );
    pager.setAdapter( adapter );
    pager.setCurrentItem( 0 );

    // Setup the tab page indicator
    TabPageIndicator indicator = ( TabPageIndicator ) findViewById( R.id.indicator );
    indicator.setViewPager( pager );
}

class MyPagerAdapter extends FragmentStatePagerAdapter {
    private SparseArray<Fragment> fragmentPageMap;

    public MyPagerAdapter(FragmentManager fm, Activity context) {
        super( fm );
        fragmentPageMap = new SparseArray<Fragment>();
    }

    @Override
    public Fragment getItem(int index) {
        switch ( index ) {
        case 0:
            if ( fragmentPageMap.get( index ) != null ) {
                SherlockListFragment scheduleFragment =  ScheduleListFragment.newInstance();
                fragmentPageMap.put( index, scheduleFragment );
                return scheduleFragment;
            } else {
                return fragmentPageMap.get( index );
            }
        default:
            return null;
        }
    }

    /*@Override
    public void destroyItem(View container, int index, Object object) {
        super.destroyItem( container, index, object );
        fragmentPageMap.remove( index );
    }*/

    @Override
    public CharSequence getPageTitle(int index) {
        return ( ( ViewPagerPage ) fragmentPageMap.get( index ) ).getTitle();
    }

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

public interface ViewPagerPage {
    String getTitle();
}

主要 Activity 布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<com.viewpagerindicator.TabPageIndicator
    android:id="@+id/indicator"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:textStyle="bold" />

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="1" />

</LinearLayout>

调度列表 fragment

public class ScheduleListFragment extends SherlockListFragment implements ViewPagerPage {

private ScheduleAdapter adapter;
private final String TITLE = "Schedule";

public static ScheduleListFragment newInstance() {
    ScheduleListFragment newFrag = new ScheduleListFragment();
    Bundle args = new Bundle();
    newFrag.setArguments( args );
    return newFrag;
}

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return inflater.inflate( R.layout.fragment_schedule_list, null );
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate( R.menu.fragment_schedule_list, menu );
}

// Container Activity must implement this interface
public interface OnAddItemClickedListener {
    public void onAddItemClicked();
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle item selection
    switch ( item.getItemId() ) {
    case R.id.add_item:
        Intent myIntent = new Intent( getActivity(), AddScheduleItemActivity.class );
        startActivityForResult( myIntent, 1 );

        return true;
    default:
        return super.onOptionsItemSelected( item );
    }
}

public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated( savedInstanceState );
    setHasOptionsMenu( true );

    adapter = new ScheduleAdapter( getActivity() );

    setListAdapter( adapter );
}

private class SampleItem {
    public String tag;
    public int iconRes;

    public SampleItem(String tag, int iconRes) {
        this.tag = tag;
        this.iconRes = iconRes;
    }
}

public class ScheduleAdapter extends ArrayAdapter<SampleItem> {

    public ScheduleAdapter(Context context) {
        super( context, 0 );
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        if ( convertView == null ) {
            convertView = LayoutInflater.from( getContext() ).inflate( R.layout.results_list_row, null );
        }
        ImageView icon = ( ImageView ) convertView.findViewById( R.id.row_icon );
        icon.setImageResource( getItem( position ).iconRes );
        TextView title = ( TextView ) convertView.findViewById( R.id.row_title );
        title.setText( getItem( position ).tag );

        return convertView;
    }

}

@Override
public String getTitle() {
    return TITLE;
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if ( resultCode == android.app.Activity.RESULT_OK ) {
        String name = ( String ) data.getExtras().get( "TEXT" );
        Toast.makeText( getActivity(), name, Toast.LENGTH_LONG ).show();
    }
}

fragment 布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ListView
    android:id="@android:id/list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" />

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="TextView" />

</LinearLayout>

谢谢，弥敦道

当前的解决方案:

更改适配器构造函数以初始化第一个 fragment 并将其添加到内部映射。有没有人认为这样做有什么问题，或者有没有改进上面发布的任何代码的方法？谢谢!

public MyPagerAdapter(FragmentManager fm, Activity context) {
        super( fm );
        fragmentPageMap = new SparseArray<Fragment>();
        SherlockListFragment scheduleFragment = ScheduleListFragment.newInstance();
        fragmentPageMap.put( 0, scheduleFragment );
    }

Answer 1

getCount() 在 MyPagerAdapter 中返回 0，因此不会创建 Fragment，如果需要 N，它应该返回 N 要实例化的 fragment 。

fragmentPageMap 在构造函数中创建，当调用 getCount() 并且在 getItem 之前调用 getCount() 时为空(index)，这就是 getCount() 返回 0

的原因

在这种情况下，您不需要开关，因为您每次都在实例化相同的 fragment 。但如果您在实例化不同的 fragment 时需要它。

@Override
public Fragment getItem(int index) {
  switch (index) {
    case 0:
      return new Fragment1();
    case 1:
      return new Fragment2();
  }
  return null;
}