如何实现列表视图的OnScrollListener？？

Question

我从服务器获得500条记录。我想在列表视图中显示10个项目，当列表视图到达末尾时，我需要加载另外10个项目，以此类推。我在网上看过很多例子，但是我无法解决这个问题，请帮帮我。

下面是我的代码：

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.form);
    Seen = (ImageView) findViewById(R.id.SeenStatus);       


    new GetDescendingDate().execute();
    userArray = new ArrayList<listmodel>();

    ListView lv = getListView();


    lv.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String Id = ((TextView) view.findViewById(R.id.txtId))
                    .getText().toString();

            // Starting single activity
            Intent in = new Intent(getApplicationContext(),
                    details.class);
            in.putExtra("TAG_Id", Id);
            startActivity(in);


    });



    }

}


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

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(Atab.this);
        pDialog.setMessage("Loading...");
        pDialog.setCancelable(false);
        pDialog.show();

    }

    @TargetApi(Build.VERSION_CODES.GINGERBREAD)
    @Override
    protected Void doInBackground(Void... arg0) {

        JSONParser jParser = new JSONParser();

        // Getting JSON Array node
        JSONArray json;

        session = new SessionManager(getApplicationContext());
        session.checkLogin();
        HashMap<String, String> user = session.getUserDetails();
        String email = user.get(SessionManager.KEY_EMAIL);
        String Status = "New";
        String get;
        get = URL.Get;
        String url_new = get + email + "/" + Status + "/" + "SODD"
                + "/" + "null" + "/" + "0" + "/" + "10";
        try {
            json = jParser.getJSONFromUrl(url_new);

            if (json != null) {
                // looping through All Orders
                for (int i = 0; i < json.length(); i++) {
                    try {
                        JSONObject c = json.getJSONObject(i);

                        String number = c.getString("No");
                        String By = c.getString("By");
                        String Type = c.getString("Type");
                        String Descripton = c.getString("Desc");
                        String Date = c.getString("DateTime");
                        String Id = c.getString("Id");
                        String ONo = c.getString("ONo");
                        String FirstName = c        .getString("FirstName");
                        String Price = c.getString("Price");


                        listmodel list = new listmodel();
                        list.setId(Id);
                        list.setBy(By);
                        list.setType(Type);
                        list.setDescription(Descripton);
                        list.setDate(Date);
                        list.setPrice(Price);
                        list.setName(FirstName);

                        userArray.add(list);

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }

            else {
                Log.e("New", "Couldn't get any data from the url");

            }
        } catch (JSONException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        return null;
    }

    protected void onPostExecute(Void result) {
        super.onPostExecute(result);

        if (pDialog.isShowing())
            pDialog.dismiss();

        adapter = new adapter(Atab.this,userArray);         
        setListAdapter(adapter);


    }

}

Answer 1

你可以像这样实现..

 listView.setOnScrollListener(new OnScrollListener() {
        private int currentVisibleItemCount;
        private int currentScrollState;
        private int currentFirstVisibleItem;
        private int totalItem;
        private LinearLayout lBelow;


        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            // TODO Auto-generated method stub
            this.currentScrollState = scrollState;
            this.isScrollCompleted();               
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem,
                int visibleItemCount, int totalItemCount) {
            // TODO Auto-generated method stub
            this.currentFirstVisibleItem = firstVisibleItem;
            this.currentVisibleItemCount = visibleItemCount;
            this.totalItem = totalItemCount;


        }

        private void isScrollCompleted() {
            if (totalItem - currentFirstVisibleItem == currentVisibleItemCount
                    && this.currentScrollState == SCROLL_STATE_IDLE) {
             /** To do code here*/


        }
    });

Answer 2

最简单的选择

首先，您需要添加列表脚注并分配OnScrollListener

ProgressBar footer = new ProgressBar(this);
listView.addFooterView(footer);
listView.setOnScrollListener(scrollListener);

而这个实现OnScrollListener

private AbsListView.OnScrollListener scrollListener = new AbsListView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {

        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            int lastInScreen = firstVisibleItem + visibleItemCount;
            if(lastInScreen == totalItemCount && !isLoading){
                loadMoreItems(totalItemCount - 1);
                isLoading = true;
            }
        }
    };

服务器给了我10个元素的记录

下载完成后，isLoading会更改

totalItemCount - 1 start position(footer也是列表中的一个元素)

完成后，您需要向适配器adapter.addAll(list);添加新元素，并执行adapter.notifyDataSetChanged ();并将isLoading = false;

Answer 3

如下所示：

public OnScrollListener scrollListener = new OnScrollListener() 
{
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) 
    { 
         if((firstVisibleItem + visibleItemCount) >= totalItemCount) && /*also maybe some condition else*/) 
         {    

             //here start next 10 items request                   
         }


    @Override
    public void onScrollStateChanged(AbsListView arg0, int arg1) {
            // TODO Auto-generated method stub

    }

};

如果您的服务器在每次休息时都像nextUrl一样给出下10个条目请求URL，那么您可以检查nextUrl是否为null，如果null意味着没有更多的条目可用，那么您可以检查condition else中是否没有。

最后，记住将listener设置为您的ListView：

yourListView.setOnScrollListener(scrollListener);