Question

我正在尝试在listview中添加一个加载图标作为footerView。但是当我滚动并将新数据附加到listview时我得到ClassCastException，我的应用程序已关闭

我在LoadMoreXML类执行时得到异常

任何人都可以帮助我吗？

这是我的代码

主要片段

public class LayoutActivity extends Fragment implements OnScrollListener{

    ListView listview;
    ListItemAdapter theAdapter;
    ListItemAdapter myExistingAdapter = null;
    String URL = "http://localhost/api/question/get_newest_except/0/0/5";
    ProgressDialog pDialog;
    NodeList nodelist;
    ArrayList<ListItemObject> data;
    Integer counter=0;

    public LayoutActivity() {
        super();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootview = inflater.inflate(R.layout.layout_main, container,false);
        listview = (ListView) rootview.findViewById(R.id.list01);
        ProgressBar spinner = new ProgressBar(this.getActivity());
        listview.addFooterView(spinner);

        new DownloadXML().execute(URL);
        listview.setOnScrollListener(this);
        return rootview;
    }
    public class DownloadXML extends AsyncTask<String, Void, Void>{

        public DownloadXML() {
            super();
        }

        @Override
        protected void onPreExecute() {

        }

        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            data = new ArrayList<ListItemObject>();
            ListItemObject itemData;

            try{
                for (int temp = 0; temp < nodelist.getLength(); temp++) {
                    Node nNode = nodelist.item(temp);
                    if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                        Element eElement = (Element) nNode;
                        itemData = new ListItemObject();

                        itemData.setId(getNode("pb__question__id",eElement));
                        itemData.setOwner(getNode("pb__question__consumer__id",eElement));
                        if(!getNode("pb__question__consumer__id",eElement).equalsIgnoreCase("0")){
                            itemData.setName(getNode("pb__question__consumer__name",eElement));
                            itemData.setJob(getNode("pb__question__consumer__occupation", eElement));
                            itemData.setProfilePic(getNode("pb__question__consumer__pp",eElement));
                        }
                        itemData.setStatus(getNode("pb__question__title",eElement));
                        itemData.setExtras(getNode("pb__question__topic__name", eElement));
                        if(!getNode("att__pict",eElement).isEmpty()){
                            itemData.setImage(getNode("att__pict", eElement));
                        }

                        if(getNode("pb__question__type", eElement).equalsIgnoreCase("1")){
                            itemData.setOpini(getNode("pb__question__total__opini", eElement));
                        }else if(getNode("pb__question__type", eElement).equalsIgnoreCase("2") || getNode("pb__question__type", eElement).equalsIgnoreCase("3")){
                            itemData.setOpini(getNode("pb__question__total__polling", eElement));
                        }else if(getNode("pb__question__type", eElement).equalsIgnoreCase("4")){
                            itemData.setOpini(getNode("pb__question__total__rating", eElement));
                        }

                        itemData.setTipe(getNode("pb__question__type", eElement));
                        itemData.setIkuti(getNode("pb__question__total__follow", eElement));
                        itemData.setSebarkan(getNode("pb__question__total__share", eElement));

                        data.add(itemData);
                    }
                }
                theAdapter = new ListItemAdapter(LayoutActivity.this.getActivity(),data);
                listview.setAdapter(theAdapter);

            }catch(Exception e){
                Toast.makeText(getActivity(), "Koneksi dengan server gagal" , Toast.LENGTH_SHORT).show();
            }

        }

        @Override
        protected Void doInBackground(String... Url) {
            try {
                URL url = new URL(Url[0]);
                DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
                DocumentBuilder db = dbf.newDocumentBuilder();
                Document doc = db.parse(new InputSource(url.openStream()));
                doc.getDocumentElement().normalize();
                nodelist = doc.getElementsByTagName("pb__question");

            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return null;
        }

    }

    public class LoadMoreXML extends AsyncTask<String, Void, Void>{
        ArrayList<ListItemObject> data;

        public LoadMoreXML() {
            super();
        }

        @Override
        protected void onPreExecute() {

        }

        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            data = new ArrayList<ListItemObject>();
            ListItemObject itemData;
                for (int temp = 0; temp < nodelist.getLength(); temp++) {
                    Node nNode = nodelist.item(temp);
                    if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                        Element eElement = (Element) nNode;
                        itemData = new ListItemObject();

                        itemData.setId(getNode("pb__question__id",eElement));
                        itemData.setOwner(getNode("pb__question__consumer__id",eElement));
                        if(!getNode("pb__question__consumer__id",eElement).equalsIgnoreCase("0")){
                            itemData.setName(getNode("pb__question__consumer__name",eElement));
                            itemData.setJob(getNode("pb__question__consumer__occupation", eElement));
                            itemData.setProfilePic(getNode("pb__question__consumer__pp",eElement));
                        }
                        itemData.setStatus(getNode("pb__question__title",eElement));
                        itemData.setExtras(getNode("pb__question__topic__name", eElement));
                        if(!getNode("att__pict",eElement).isEmpty()){
                            itemData.setImage(getNode("att__pict", eElement));
                        }

                        if(getNode("pb__question__type", eElement).equalsIgnoreCase("1")){
                            itemData.setOpini(getNode("pb__question__total__opini", eElement));
                        }else if(getNode("pb__question__type", eElement).equalsIgnoreCase("2") || getNode("pb__question__type", eElement).equalsIgnoreCase("3")){
                            itemData.setOpini(getNode("pb__question__total__polling", eElement));
                        }else if(getNode("pb__question__type", eElement).equalsIgnoreCase("4")){
                            itemData.setOpini(getNode("pb__question__total__rating", eElement));
                        }

                        itemData.setTipe(getNode("pb__question__type", eElement));
                        itemData.setIkuti(getNode("pb__question__total__follow", eElement));
                        itemData.setSebarkan(getNode("pb__question__total__share", eElement));

                        data.add(itemData);
                    }
                }

                myExistingAdapter = (ListItemAdapter) listview.getAdapter();
                myExistingAdapter.addItems(data);
        }

        @Override
        protected Void doInBackground(String... Url) {
            try {
                URL url = new URL(Url[0]);
                DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
                DocumentBuilder db = dbf.newDocumentBuilder();
                Document doc = db.parse(new InputSource(url.openStream()));
                doc.getDocumentElement().normalize();
                nodelist = doc.getElementsByTagName("pb__question");

            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return null;
        }

    }

    private static String getNode(String sTag, Element eElement) {
        NodeList nlList = eElement.getElementsByTagName(sTag).item(0).getChildNodes();
        Node nValue = (Node) nlList.item(0);
        String result = "";
        if(nValue!=null){
            result = nValue.getNodeValue();
        }
        return result;
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub
        int threshold = 2;
        int count = listview.getCount();
        if(scrollState == SCROLL_STATE_IDLE){

            if(listview.getLastVisiblePosition() >= count - threshold){
                counter+=5;
                new LoadMoreXML().execute("http://localhost/api/question/get_newest_except/0/"+counter+"/5");
            }
        }
    }
}

这是错误日志

enter image description here

谢谢

Answer 1

当你调用listview.addFooterView时，Android正在为你创建一个支持页脚的适配器。然后，当您调用setAdapter时，Android不会替换它创建的适配器，但它仍会保留ListItemAdapter并将大多数适配器请求委托给该对象。然后，当您将ListView的适配器强制转换为类时，会崩溃，因为您的适配器实际上位于支持页脚的包装器适配器中。这有意义吗？

您需要做的是在onCreateView中创建ListItemAdapter，并立即将其附加到ListView。请注意，只要您调用addFooterView，ListView的适配器实际上是一个不同的适配器，但您的适配器仍在新的适配器中。

public class LayoutActivity extends Fragment implements OnScrollListener{
    ListItemAdapter theAdapter; // don't need myExistingAdapter any more

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootview = inflater.inflate(R.layout.layout_main, container,false);
        listview = (ListView) rootview.findViewById(R.id.list01);

        // Create your adapter with no initial data
        theAdapter = new ListViewAdapter(LayoutActivity.this.getActivity(), null);
        listview.setAdapter(theAdapter);

现在完成你的任务，只需直接引用适配器，然后添加项目：

public class DownloadXML extends AsyncTask<String, Void, Void>{
    @Override
    protected void onPostExecute(Void result) {
        ...
        theAdapter.addItems(data);

public class LoadMoreXML extends AsyncTask<String, Void, Void>{
    @Override
    protected void onPostExecute(Void result) {
        ...
        theAdapter.addItems(data);

尝试在listview上加载更多时出现ClassCastException

1 个答案: