Question

我对listview的滚动有问题。我有一个类：

private int itemsPerPage = 6;
private int count = 0;
private boolean loadingMore = false;
private ArrayList<Item> item;
private ListItemAdapter adapter;
View footerView;
private JSONArray array;
private String json;

protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.menu);
    lvListItem = (ListView) findViewById(R.id.lvListItem);
    item = new ArrayList<Item>();
    footerView = ((LayoutInflater)this.getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.list_footer, null, false);

    json = new JSONParse()
                    .getData("....");
    array = new JSONArray(json);

    load();
    adapter = new ListItemAdapter(this, 0, item);
    lvListItem.addFooterView(footerView);
    lvListItem.setAdapter(adapter);

    lvListItem.setOnScrollListener(new OnScrollListener() {

        public void onScrollStateChanged(AbsListView view, int scrollState) {
            // TODO Auto-generated method stub

        }

        public void onScroll(AbsListView view, int firstVisibleItem,
                int visibleItemCount, int totalItemCount) {
            // TODO Auto-generated method stub
            int lastInScreen = firstVisibleItem + visibleItemCount;

            // is the bottom item visible & not loading more already ? Load
            // more !
            if ((lastInScreen == totalItemCount) && !(loadingMore)) {
                Thread thread = new Thread(null, loadData);
                thread.start();
            }
        }
    });
    }

public void load(){
for (int i = 0; i < itemsPerPage; i++) {
    if (count == array.length()) {
        lvListItem.removeFooterView(footerView);
        break;
    }
    /*****Code to load data*******/
}
}


private Runnable loadData = new Runnable() {
    @Override
    public void run() {

        loadingMore = true;


        item = new ArrayList<Item>();


        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
        }

        load();


        runOnUiThread(returnRes);

    }
};


private Runnable returnRes = new Runnable() {
    @Override
    public void run() {


        if (item != null && item.size() > 0) {
            for (int i = 0; i < item.size(); i++)
                adapter.add(item.get(i));
        }


        if (count == array.length())
            lvListItem.removeFooterView(footerView);
        adapter.notifyDataSetChanged();

        // Done loading more.
        loadingMore = false;
    }
};

如果我只使用 load（），它会运行并且listview显示数据正常。但是当我滚动listview时，它会抛出错误：

 D/AndroidRuntime(1635): Shutting down VM
  W/dalvikvm(1635): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
   E/AndroidRuntime(1635): FATAL EXCEPTION: main
   E/AndroidRuntime(1635): java.lang.IndexOutOfBoundsException: Invalid index 6, size is 6
   E/AndroidRuntime(1635):  at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251)
   E/AndroidRuntime(1635):  at java.util.ArrayList.get(ArrayList.java:304)

我需要帮助

Answer 1

看起来你的数组只有6个元素，你试图访问索引为6的元素，这实际上是第7个元素所以

更改

itemsPerPage = 5;`

Answer 2

您的代码根本不是线程安全的。您正在从多个线程访问共享数据而不进行任何类型的锁定。在item runnable（在主线程上运行）中读取您的resultRes数组时，您的private final Object monitor = new Object(); // an ivar in your Activity数组可能正在重新初始化，这将导致看似无法超出范围的异常

创建一个用作互斥锁的对象：

item

然后，当访问共享数据（例如loadingMore和synchronized(monitor) { item = new ArrayList<Item>(); } synchronized(monitor) { if (item != null && item.size() > 0) { for (int i = 0; i < item.size(); i++) adapter.add(item.get(i)); } } synchronized(monitor) { if ((lastInScreen == totalItemCount) && !(loadingMore)) { Thread thread = new Thread(null, loadData); thread.start(); // will exit critical section before new thread execution begins } }）时，创建一个关键部分，例如：

{{1}}

等等。我会把它作为练习让你弄清楚其余的锁定应该在哪里完成。

使用listview的事件滚动加载更多数据时出错

2 个答案: