Volley 之ListView ArrayAdapter 下滑加载数据

1：MyListViewActivity.java

public class MyListViewActivity extends Activity {
    private ListView listView = null;
    private boolean mHasData = false;
    private boolean mInError = false;
    private boolean mEnd = false;
    
    private ArrayList<String> mTitles = new ArrayList<String>();
    private ArrayAdapter<String> mAdapter = null;
    private int offset = 15;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my_list_view);
        
        
        listView = (ListView)findViewById(R.id.my_listView_test);
        
        mAdapter = new ArrayAdapter<String>(
                this,
                R.layout.list_test,
                R.id.tv_title,
                mTitles
            );
        
        listView.setAdapter(mAdapter);
        listView.setOnScrollListener(new MyScrollListener());
    }
    
    @Override
    protected void onResume() {
        super.onResume();
        if (!mHasData && !mInError) {
           loadPage();
        }
    }
    
    //滚动时一直回调，直到停止滚动时才停止回调。单击时回调一次。
    //firstVisibleItem：当前能看见的第一个列表项ID（从0开始）
    //visibleItemCount：当前能看见的列表项个数（小半个也算）
    //totalItemCount：列表项共数
    public class MyScrollListener implements OnScrollListener {
        private boolean isLastRow = false;
        
        public MyScrollListener(){}
        
        @Override
        public void onScroll(AbsListView arg0, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            //判断是否滚到最后一行
            if (totalItemCount > 0 && (firstVisibleItem + visibleItemCount == totalItemCount)){
                isLastRow = true;
                Log.i("++onScroll++", "onScroll");
            }
        }
        
        @Override
        public void onScrollStateChanged(AbsListView arg0, int scrollState) {
            //当滚到最后一行且停止滚动时，执行加载
            if (!mHasData && isLastRow && scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE) {
                loadPage();
                isLastRow = false;
                Log.i("++loadPage++", "loadPage");
            }
            
            if(!mEnd && mHasData && isLastRow){
                Toast.makeText(MyListViewActivity.this, "数据全部加载完毕！", Toast.LENGTH_SHORT).show();
                mEnd = true;
            }
        }
    }
    
    private void loadPage() {
        int startIndex = mTitles.size();
        RequestQueue rQueue = MyVolley.getRequestQueue(); 
        String url = "http://192.168.0.116/wsht/server/selectTitle2json.php?offset="
                +offset+"&startIndex="+startIndex;
        JsonArrayRequest req = new JsonArrayRequest(
                url,
                createGetTitlesSuccess(),
                createGetTitlesError()
            );
        rQueue.add(req);
    }
    private Response.Listener<JSONArray> createGetTitlesSuccess(){
        return new Response.Listener<JSONArray>() {
            @Override
            public void onResponse(JSONArray response) {
                int len = response.length();
                
                if(len < offset){    //此时，说明数据已经全部加载完毕
                    mHasData = true;    //true表示没有数据了
                }
                
                JSONObject temp = null;
                
                try{
                    for(int i = 0; i < len; i++){
                        //从JSONArray中获取每个JSONObject对象
                        temp = response.getJSONObject(i);
                        String id = temp.getString("id");
                        String title = temp.getString("title");
                        
                        mTitles.add(id+"---"+title);
                    }
                    mAdapter.notifyDataSetChanged();
                }catch(JSONException e){
                    showErrorDialog();
                }
            }
        };
    }
    private Response.ErrorListener createGetTitlesError(){
        return new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError arg0) {
                showErrorDialog();
            }
        };
    }
    
    private void showErrorDialog() {
        mInError = true;
        AlertDialog.Builder b = new AlertDialog.Builder(MyListViewActivity.this);
        b.setMessage("网络异常，加载数据失败！");
        b.show();
    }
}

 2：使用PHP+mysql 作为服务端

<?php
    require_once '../mysql/MysqlTool.class.php';
    
    $mt=new MysqlTool();
    
    $offset = $_GET['offset'];
    $startIndex = $_GET['startIndex'];
    
    $begin = $startIndex;
    
    $sql="select id,title from test limit $begin, $offset";
    
    echo json_encode($mt->select($sql));
?>