ListView onScroll添加更多项目

Question

    private class getArticles extends AsyncTask<Void, Void, Void> {

    String url;

    getArticles(String paramUrl) {
        this.url = paramUrl;
    }


    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        mProgressDialog = new ProgressDialog(App.this);
        mProgressDialog.setMessage("U?itavanje artikala...");
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setCancelable(false);
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {

        arraylist = new ArrayList<>();

        try {

            Document document = Jsoup.connect(url).get();
            Elements els = document.select("ul.category3 > li");

            for (Element el : els) {

                HashMap<String, String> map = new HashMap<>();

                Elements slika = el.select("div.category3-image > a > img");
                Elements naslov = el.select("div.category3-text > a.main-headline");
                Element datum_noformat = el.select("div.category3-text > div.headlines-info > ul.headlines-info > li").first();
                Element datum = datum_noformat.html(datum_noformat.html().replaceAll("Posted ", ""));
                Elements desc = el.select("div.category3-text > p");
                Elements link = el.select("div.category3-text > a.main-headline");
                Element br_kom = el.select("div.category3-text > div.headlines-info > ul.headlines-info > li.comments-icon").first();

                map.put("naslov", naslov.text());
                map.put("datum", datum.text());
                map.put("desc", desc.text());
                map.put("ikona", slika.attr("src"));
                map.put("link", link.attr("abs:href"));
                map.put("brkom", br_kom.text());
                arraylist.add(map);


            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        listview = (ListView) findViewById(R.id.listview);
        adapter = new ArtikliAdapter(App.this, arraylist);
        listview.setAdapter(adapter);
        mProgressDialog.dismiss();
    }

我搜索了很多onlistview滚动的代码,但不知道如何实现它.问题是,当我调用我的asynctask时,我有一个url param,就像new getArticles("http://example.com").execute();

我想实现一个onscrolllistener,但它是这样的,我的param通常设置为:http://www.example.com/category/categoryname/,所以第二页就像http://www.example.com/category/categoryname/page/2/,第三页一样,http://www.example.com/category/categoryname/page/3/依此类推.每个页面都有7个需要解析的项目.

我怎么能实现onscrolllistener,因为url param？

提前致谢.

Answer 1

基于此链接,我编写了以下解决方案,以异步方式将元素(一次30个元素,即页面大小= 30)添加到listview.

创建一个名为EndlessListView的类,如下所示:

public class EndlessListView extends ListView implements OnScrollListener {

private View footer;
private boolean isLoading;
private EndlessListener listener;// listner
private EndlessAdapter endlessAdapter;// adapter.

private int maxNoOfElement;

public EndlessListView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    this.setOnScrollListener(this);
}

public EndlessListView(Context context, AttributeSet attrs) {
    super(context, attrs);
    this.setOnScrollListener(this);
}

public EndlessListView(Context context) {
    super(context);
    this.setOnScrollListener(this);
}

public void setListener(EndlessListener listener) {
    this.listener = listener;
}

@Override
public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {

    if (getAdapter() == null)
        return;

    if (getAdapter().getCount() == 0 || getAdapter().getCount() <= 5)
        return;

    int l = visibleItemCount + firstVisibleItem;
    if (l >= totalItemCount && !isLoading) {
        // It is time to add new data. We call the listener
        Log.e("LOAD", "DATA");
        isLoading = true;
        listener.loadData();

    }
}

public void setMaxElemnt(int maxNoOfElement) {
    this.maxNoOfElement = maxNoOfElement;
}

@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}

public void setLoadingView(int resId) {
    LayoutInflater inflater = (LayoutInflater) super.getContext()
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    footer = (View) inflater.inflate(resId, null);
    this.addFooterView(footer);
}

public void setAdapter(EndlessAdapter adapter) {
    super.setAdapter(adapter);
    this.endlessAdapter = adapter;

}

public void addNewData(List<Integer> data) {
    endlessAdapter.setData(data);
    endlessAdapter.notifyDataSetChanged();
    isLoading = false;
}

public static interface EndlessListener {
    public void loadData();

}

 }

在此之后我们必须为它创建适配器,称为

EndlessAdapter

public class EndlessAdapter extends BaseAdapter {
private List<Integer> mIntegers;
private Context context;

public EndlessAdapter(Context context) {
    this.context = context;
}

public void setData(List<Integer> mIntegers) {
    this.mIntegers = mIntegers;
}

@Override
public int getCount() {
    if (mIntegers == null)
        return 0;
    return mIntegers.size();
}

@Override
public Integer getItem(int index) {

    if (mIntegers == null) {
        return null;
    } else {
        return mIntegers.get(index);
    }
}

@Override
public long getItemId(int arg0) {
    // TODO Auto-generated method stub
    return 0;
}

class ViewHolder {
    TextView textView;
}

@Override
public View getView(int index, View view, ViewGroup viewGroup) {
    ViewHolder holder;
    if (view == null) {
        holder = new ViewHolder();
        view = ((LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE))
                .inflate(R.layout.rows, viewGroup, false);
        holder.textView = (TextView) view.findViewById(R.id.mtext);
        view.setTag(holder);

    } else {
        holder = (ViewHolder) view.getTag();
    }
    holder.textView.setText(getItem(index) + "");
    return view;
}

   }

现在在xml的活动中我们可以使用EndlessListView(在com.example.stackoverflow包中),如下所示:

<RelativeLayout 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" >

<com.example.stackoverflow.EndlessListView
    android:id="@+id/endlessListView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

</RelativeLayout>

完成此步骤后,我们需要在MainActivity中进行以下更改

    public class MainActivity extends Activity implements EndlessListener {
private EndlessAdapter adapter;
private EndlessListView endlessListView;
private List<Integer> data;
private int gStartIndex = 30;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    endlessListView = (EndlessListView) findViewById(R.id.endlessListView);
    adapter = new EndlessAdapter(this);
    data = new ArrayList<Integer>();

    endlessListView.setLoadingView(R.layout.footer);
    // endlessListView.showFooter();
    endlessListView.setListener(this);
    endlessListView.setAdapter(adapter);
    gStartIndex = 0;
    fillData(gStartIndex);
}

private void fillData(int startIndex) {

    new AsyncLoadData().execute(startIndex);

}

@Override
public void loadData() {

    fillData(gStartIndex);

}

private class AsyncLoadData extends AsyncTask<Integer, Integer, Void> {

    @Override
    protected Void doInBackground(Integer... params) {
        int gendIndex = params[0] + 30;
        gStartIndex = gendIndex;
        /***
         * Here you could add your n/w code. To simulate the n/w comm. i am
         * adding elements to list and making it sleep for few sec.
         * */
        for (int i = params[0]; i < gendIndex; i++) {
            publishProgress(i);

        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);
        data.add(values[0]);
    }

    @Override
    protected void onPostExecute(Void result) {
        endlessListView.addNewData(data);
    }
}

    }

Answer 2

我刚刚发现的这个自定义ScrollListViewOnBottomReachedListener可以从您的Activity或 中实现Fragment，并在用户点击页面底部时接收事件。您还需要跟踪当前页面以及何时点击底部以下载下一页。最新数据应该添加到现有数据中ArrayList，并且您应该调用notifyDataSetChanged()适配器以便ListView可以呈现新数据。您不必创建新的适配器，只需更新您的ArrayList.

如果您支持方向更改，则必须保存onSaveInstanceState()当前页码，以便在重新创建Activity或时Fragment可以从正确的页面继续。并且您必须保证ArrayList数据源免受配置更改的影响，因为您不想再次下载它。我建议使用Fragmentwith setRetainInstance()set trueto persist ArrayList。

这是我使用 RetainFragment 保存数据的自定义代码：

/**
 * A simple non-UI Fragment that stores a single Object
 * and is retained over configuration changes.
 */
public class RetainFragment<E extends Object> extends Fragment {

    /** Object for retaining. */
    private E mObject;

    /**
     * Empty constructor as per the Fragment documentation
     */
    public RetainFragment() {}

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

        // Make sure this Fragment is retained over a configuration change
        setRetainInstance(true);
    }

    /**
     * Store a single object in this Fragment.
     *
     * @param object The object to store
     */
    public void setObject(E object) {
        mObject = object;
    }

    /**
     * Get the stored object.
     *
     * @return The stored object
     */
    public E getObject() {
        return mObject;
    }
}

RetainFragment您的使用示例Activity：

FragmentManager fm = getFragmentManager();
mRetainFragment = (RetainFragment<ArrayList>) fm.findFragmentByTag(RETAIN_FRAG);
if (mRetainFragment == null) {
    mRetainFragment = new RetainFragment<>();
    mRetainFragment.setObject(new ArrayList());
    fm.beginTransaction().add(mRetainFragment, RETAIN_FRAG).commit();
}

ArrayList yourArrayList = mRetainFragment.getObject();
// Now your ArrayList is saved accrossed configuration changes