在notifyDataSetChanged之后Android ListView没有刷新

Question

我的ListFragment代码

public class ItemFragment extends ListFragment {

    private DatabaseHandler dbHelper;
    private static final String TITLE = "Items";
    private static final String LOG_TAG = "debugger";
    private ItemAdapter adapter;
    private List<Item> items;


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

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.setHasOptionsMenu(true);
        super.onCreate(savedInstanceState);
        getActivity().setTitle(TITLE);
        dbHelper = new DatabaseHandler(getActivity());
        items = dbHelper.getItems(); 
        adapter = new ItemAdapter(getActivity().getApplicationContext(), items);
        this.setListAdapter(adapter);

    }



    @Override
    public void onResume() {
        super.onResume();
        items.clear();
        items = dbHelper.getItems(); //reload the items from database
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);
        if(dbHelper != null) { //item is edited
            Item item = (Item) this.getListAdapter().getItem(position);
            Intent intent = new Intent(getActivity(), AddItemActivity.class);
            intent.putExtra(IntentConstants.ITEM, item);
            startActivity(intent);
        }
    }
}

我的ListView

<?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" >

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

</LinearLayout>

但这并没有刷新ListView.即使重新启动应用程序后,也不会显示更新的项目.我的ItemAdapter延伸BaseAdapter

public class ItemAdapter extends BaseAdapter{

    private LayoutInflater inflater;
    private List<Item> items;
    private Context context;

    public ProjectListItemAdapter(Context context, List<Item> items) {
        super();
        inflater = LayoutInflater.from(context);
        this.context = context;
        this.items = items;

    }

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

    @Override
    public Object getItem(int position) {
        return items.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ItemViewHolder holder = null;
        if(convertView == null) {
            holder = new ItemViewHolder();
            convertView = inflater.inflate(R.layout.list_item, parent,false);
            holder.itemName = (TextView) convertView.findViewById(R.id.topText);
            holder.itemLocation = (TextView) convertView.findViewById(R.id.bottomText);
            convertView.setTag(holder);
        } else {
            holder = (ItemViewHolder) convertView.getTag();
        }
        holder.itemName.setText("Name: " + items.get(position).getName());
        holder.itemLocation.setText("Location: " + items.get(position).getLocation());
        if(position % 2 == 0) {                                                                                 
            convertView.setBackgroundColor(context.getResources().getColor(R.color.evenRowColor));
        } else {    
            convertView.setBackgroundColor(context.getResources().getColor(R.color.oddRowColor));
        }
        return convertView;
    }

    private static class ItemViewHolder {
        TextView itemName;
        TextView itemLocation;
    }
}

有人可以帮忙吗？

Answer 1

看看你的onResume方法ItemFragment:

@Override
public void onResume() {
    super.onResume();
    items.clear();
    items = dbHelper.getItems(); // reload the items from database
    adapter.notifyDataSetChanged();
}

你刚刚调用之前更新的notifyDataSetChanged()不是适配器的字段,private List<Item> items;而是片段的相同声明的字段.适配器仍然存储对您在创建适配器时传递的项目列表的引用(例如,在fragment的onCreate中).最短(在变化的数量意义上)但不是优雅的方式使您的代码按预期运行只是替换行:

    items = dbHelper.getItems(); // reload the items from database

同

    items.addAll(dbHelper.getItems()); // reload the items from database

更优雅的解决方案:

1)private List<Item> items;从中删除项目ItemFragment- 我们只需要在适配器中继续引用它们

2)将onCreate改为:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    super.setHasOptionsMenu(true);
    getActivity().setTitle(TITLE);
    dbHelper = new DatabaseHandler(getActivity());
    adapter = new ItemAdapter(getActivity(), dbHelper.getItems());
    setListAdapter(adapter);
}

3)在ItemAdapter中添加方法:

public void swapItems(List<Item> items) {
    this.items = items;
    notifyDataSetChanged();
}

4)将你的onResume更改为:

@Override
public void onResume() {
    super.onResume();
    adapter.swapItems(dbHelper.getItems());
}

Answer 2

您将重新加载的项目分配给全局变量项目onResume(),但这不会反映在ItemAdapter类中,因为它有自己的实例变量名为"items".

要刷新ListView,请在ItemAdapter类中添加一个refresh(),该类接受列表数据,即项目

class ItemAdapter
{
    .....

    public void refresh(List<Item> items)
    {
        this.items = items;
        notifyDataSetChanged();
    } 
}

onResume()使用以下代码更新

@Override
public void onResume()
{
    super.onResume();
    items.clear();
    items = dbHelper.getItems(); //reload the items from database
    **adapter.refresh(items);**
}

Answer 3

在onResume()中更改此行

items = dbHelper.getItems(); //reload the items from database

至

items.addAll(dbHelper.getItems()); //reload the items from database

问题是你永远不会告诉适配器有关新项目列表的信息.如果您不想将新列表传递给适配器(因为您似乎没有),那么只需items.addAll在您的适配器之后使用clear().这将确保您修改适配器引用的相同列表.