Question

我是Android新手，正在尝试使用自定义PagerAdapters和FragmentStatePagerAdapters在主 - 详细信息流中显示ViewPagers的示例应用程序。我的应用程序有一个由SQLiteDatabase管理的虚拟项目列表，其中包含标题String，描述String，Boolean状态和图像列表（I计划从String网址下载实现它们，但目前我只是尝试使用单个图像资源）。我在详细信息视图中遇到两个问题。

我的目的是使用ViewPager和FragmentStatePagerAdapter来显示详情视图，其中包含ViewPager个自定义PagerAdapter，用于显示图片列表，TextView表示标题和说明，ToggleButton表示类似状态，删除按钮表示从列表中删除项目。

的问题：

带有自定义PagerAdapter的ViewPager不显示图像。它占据了预期的空间，并且在其上执行的滑动也表现得如预期的那样。只有图像不可见。
[已解决]使用删除按钮，我可以从数据库中删除该项目，并相应地更新主视图，但我无法更新详细信息视图，并且应用程序崩溃。

这是我的代码：

调用ItemDetailActivity.java的代码

@Override
public void onClick(View v) {
    Intent detailIntent = new Intent(getContext(), ItemDetailActivity.class);
    detailIntent.putExtra(ItemDetailFragment.ARG_LIST_POSITION, holder.position);
    getContext().startActivity(detailIntent);
}

ItemDetailActivity.java

public class ItemDetailActivity extends FragmentActivity {

    static ItemDetailPagerAdapter idpa;

    static ViewPager detailPager;

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

        idpa = new ItemDetailPagerAdapter(getSupportFragmentManager());

        // Show the Up button in the action bar.
        getActionBar().setDisplayHomeAsUpEnabled(true);

        detailPager = (ViewPager) findViewById(R.id.item_detail_container);
        detailPager.setAdapter(idpa);
        detailPager.setCurrentItem(getIntent().getIntExtra(ItemDetailFragment.ARG_LIST_POSITION, 0));
    }
}

activity_item_detail.xml

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/item_detail_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.trial.piclist.ItemDetailActivity"
    tools:ignore="MergeRootFrame" />

ItemDetailFragment.java

public class ItemDetailFragment extends Fragment {
    public static final String ARG_ITEM_ID = "item_id";
    public static final String ARG_LIST_POSITION = "list_index";
    public static final String ARG_TWO_PANE = "is_two_pane";
    int position = -1;
    long id = -1;
    boolean twoPane = false;
    ViewPager pager;
    private PicItem mItem;

    public ItemDetailFragment() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        twoPane = getArguments().getBoolean(ARG_TWO_PANE, false);
        position = getArguments().getInt(ARG_LIST_POSITION, -1);
        id = getArguments().getLong(ARG_ITEM_ID, -1);
        if (id == -1)
            id = ItemListFragment.getIdByPosition(position);
        setmItem(id);
    }

    public void setmItem(long id) {
        if (id >= 0) {
            try {
                ItemListActivity.lds.open();
                mItem = ItemListActivity.lds.getById(id);
                ItemListActivity.lds.close();
            } catch (Exception e) {
                System.out.println(e.getMessage());
            }
            if (mItem != null) {
                List<String> pics = new ArrayList<String>();
                pics.add("1");
                pics.add("2");
                pics.add("3");
                pics.add("4");
                pics.add("5");
                mItem.setPics(pics);
            }
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_item_detail,
                container, false);
        DetailViewHolder holder = new DetailViewHolder();

        pager = (ViewPager) rootView.findViewById(R.id.pager);
        ImagePagerAdapter adapter = new ImagePagerAdapter(mItem, getActivity(),
                inflater, position);
        pager.setAdapter(adapter);

        holder.position = getArguments().getInt(ARG_LIST_POSITION);
        holder.ttv = (TextView) rootView.findViewById(R.id.item_title);
        holder.dtv = (TextView) rootView.findViewById(R.id.item_detail);
        holder.likeButton = (ToggleButton) rootView
                .findViewById(R.id.item_like);
        holder.deleteButton = (Button) rootView.findViewById(R.id.item_delete);
        rootView.setTag(holder);

        if (mItem != null) {

            holder.ttv.setText(mItem.getTitle());
            holder.dtv.setText(mItem.getDescription());
            holder.likeButton.setChecked(mItem.getIsLiked());
            holder.likeButton.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View v) {
                    ItemListActivity.lds.open();
                    ItemListActivity.lds.toggleLike(mItem.getId());
                    mItem.toggleIsLiked();
                    ItemListActivity.lds.close();
                    ItemListFragment.listDisplayHelper.toggleLiked(position);
                }
            });
            holder.deleteButton.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    ItemListActivity.lds.open();
                    ItemListActivity.lds.removeItem(mItem.getId());
                    ItemListActivity.lds.close();

                    ItemListFragment.listDisplayHelper.remove(position);
                    ItemListActivity.idpa.notifyDataSetChanged();
                    // What do I do so that the FragmentStatePagerAdapter is
                    // updated and the viewpager shows the next item.
                }
            });
        }

        return rootView;
    }

    static private class DetailViewHolder {
        TextView ttv;
        TextView dtv;
        ToggleButton likeButton;
        Button deleteButton;
        int position;
    }
}

fragment_item_detail.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context="com.trial.piclist.ItemDetailFragment" >
    <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="200dip">
    </android.support.v4.view.ViewPager>

    <TableRow
        android:id="@+id/tableRow1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <TextView
            android:id="@+id/item_title"
            style="?android:attr/textAppearanceLarge"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/hello"
            android:textIsSelectable="true" />

        <Space
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_weight="1" />

        <include
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            layout="@layout/controls_layout" />
    </TableRow>

    <ScrollView
        android:id="@+id/descScrollView"
        android:layout_width="match_parent"
        android:layout_height="0dip"
        android:layout_weight="1" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical" >

            <TextView
                android:id="@+id/item_detail"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/hello" />
        </LinearLayout>
    </ScrollView>

</LinearLayout>

controls_layout.xml

<?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="horizontal" >

<ToggleButton
    android:id="@+id/item_like"
    android:layout_width="30dip"
    android:layout_height="30dip"
    android:layout_gravity="right"
    android:background="@android:drawable/btn_star"
    android:gravity="center"
    android:text="@string/like_list_item"
    android:textOff="@string/empty_text"
    android:textOn="@string/empty_text" />

<Button
    android:id="@+id/item_delete"
    style="?android:attr/buttonStyleSmall"
    android:layout_width="30dip"
    android:layout_height="30dip"
    android:background="@android:drawable/ic_menu_delete"
    android:text="@string/empty_text" />

</LinearLayout>

自定义PagerAdapter 的 ImagePagerAdapter.java

public class ImagePagerAdapter extends PagerAdapter {
    LayoutInflater inflater;
    List<View> layouts = new ArrayList<>(5);

    // Constructors.

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        if (layouts.get(position) != null) {
            return layouts.get(position);
        }
        View layout = inflater.inflate(R.layout.detail_image, 
            ((ViewPager) container), true);
        try {
            ImageView loadSpace = (ImageView) layout
                    .findViewById(R.id.detail_image_view);
            loadSpace.setBackgroundColor(0x000000);
            loadSpace.setImageResource(R.drawable.light_grey_background);
            loadSpace.setAdjustViewBounds(true);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        layout.setTag(images.get(position));
        layouts.set(position, layout);
        return layout;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
    }

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

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return (((View) object).findViewById((view.getId())) != null);
    }

}

FragmentPagerAdapter 的 ItemDetailPagerAdapter.java

public class ItemDetailPagerAdapter extends FragmentStatePagerAdapter {

    public ItemDetailPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        Fragment fragment = new ItemDetailFragment();
        Bundle args = new Bundle();
        args.putLong(ItemDetailFragment.ARG_ITEM_ID, ItemListFragment.getIdByPosition(position));
        args.putInt(ItemDetailFragment.ARG_LIST_POSITION, position);
        args.putBoolean(ItemDetailFragment.ARG_TWO_PANE, ItemListActivity.mTwoPane);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public int getCount() {
        openDatabase();
        int c = database.getCount();
        closeDatabase();
        return c;
    }

    @Override
    public int getItemPosition(Object object) {
        long mId = ((ItemDetailFragment) object).getmId();
        int pos = POSITION_NONE;
        openDatabase();
        if (database.contains(mId)) {
            pos = database.getPositionById(mId);
        }
        closeDatabase();
        return pos;
    }
}

非常感谢任何帮助。谢谢:)）

Answer 1

在你的ItemDetailFragment中，从持有者中删除viewpager，它应该直接进入返回的视图，如下所示：

public View onCreateView(LayoutInflater inflater, ViewGroup container,
    Bundle savedInstanceState) {

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

    pager = (ViewPager) rootView.findViewById(R.id.pager);
    ImagePagerAdapter adapter = new ImagePagerAdapter(mItem, getActivity(),inflater, position);
    pager.setAdapter(adapter);

    return rootView;
}

并且ViewHolder模式应该应用于PagerAdapter。

Answer 2

在ImagePagerAdapter.java中，更正isViewFromObject方法 -

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

这将更正ImageView。

在ItemDetailPagerAdapter.java中，覆盖getItemPosition方法 -
```
@Override
public int getItemPosition(Object object) {
    int ret = POSITION_NONE;
    long id = ((ItemDetailFragment) object).getId();
    openDatabase();
    if (databaseContains(id)) {
        ret = positionInDatabase(id);
    }
    closeDatabase();
    return ret;
}
```
删除时调用FragmentStatePagerAdapter.NotifyDataSetChanged()方法。这将使适配器在删除时自行更新。尽管如此，FragmentStatePagerAdapter使用片段列表和存储状态来实现适配器。这也造成了麻烦。要删除它，请实现自己的碎片列表。

ViewPager和PagerAdapter

2 个答案: