告诉Android AsyncTaskLoader以检索更多数据

Question

让我首先说这不是关于滚动ListViews的问题.我不想知道如何判断用户何时滚动到列表的底部,所以请不要给我这个问题的答案,或者将其标记为重复.

我正在使用一个扩展AsyncTaskLoader的类来使用来自Web服务的数据填充ListView.

最初,我加载50件物品,一切都很好.我需要知道如何告诉Loader以递增方式加载下50个项目.我理解在ListView代码中要执行此操作,但我无法找出告诉Loader我想要加载更多数据而不重置它并再次加载所有内容的最佳方法.

再说一次,澄清一下,我在这里要解决的问题只是通知加载器需要加载更多数据.它已经知道如何在第二次调用loadInBackground()时加载更多数据,并且ListView已经知道在何时/何时通知Loader,问题是如何.

一些相关代码:

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

    m_adapter = new SearchAdapter(getActivity());
    setListAdapter(m_adapter);

    // if the loader doesn't already exist, one will be created
    // otherwise the existing loader is reused so we don't have
    // to worry about orientation and other configuration changes
    getLoaderManager().initLoader(SEARCH_LOADER_ID, null, this);
}

@Override
public Loader<List<Result>> onCreateLoader(int id, Bundle args)
{
    String query = args != null ? args.getString(QUERY_KEY) : "";
    return new SearchLoader(getActivity(), query);
}

private class SearchAdapter extends ArrayAdapter<Result>
{
    // ...

    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {

        // ...

        if (position == getCount() - 2)
            // TODO: Need to notify Loader here

        // ...
    }
}

private static class SearchLoader extends OurAsyncTaskLoader<List<Result>>
{
    public SearchLoader(Context context, String query)
    {
        super(context);

        m_query = query;
        m_data = Lists.newArrayList();
        m_loadedAllResults = false;
    }

    @Override
    public List<Result> loadInBackground()
    {
        if (m_loadedAllResults)
            return m_data;

        // the Loader implementation does a == check rather than a .equals() check
        // on the data, so we need this to be a new List so that it will know we have
        // new data
        m_data = Lists.newArrayList(m_data);

        MyWebService service = new MyWebService();
        List<Result> results = service.getResults(m_query, m_data.size(), COUNT);
        service.close();

        if (results == null)
            return null;

        if (results.size() < COUNT)
            m_loadedAllResults = true;

        for (Result result : results)
            m_data.add(result)

        return m_data;
    }

    private static final int COUNT = 50;

    private final String m_query;

    private boolean m_loadedAllResults;
    private List<Result> m_data;
}

Answer 1

我想出了一个有效的方法。在我的SearchAdapter#getView()方法中，我有以下代码：

private class SearchAdapter extends ArrayAdapter<Result>
{
    // ...

    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {

        // ...

        if (position == getCount() - 2)
            getLoaderManager().getLoader(SEARCH_LOADER_ID).onContentChanged();
        // ...
    }
}

我仍然想知道这是否是“最佳实践”方式，但它现在似乎解决了我的问题。