如何限制android中获取记录的listview中的记录数量

Question

我从我连接到Mysql的php脚本获取Json记录。 PHP脚本一次发送500条记录。 然后将这些记录转换为数组，并生成包含所有500条记录的列表视图。 我希望listview一次显示20条记录，当用户到达listview的底部时，接下来应显示20条记录。

用于此活动的代码bieng是

public class ListActivity extends AppCompatActivity implements AsyncResponse, AdapterView.OnItemClickListener {
final String LOG = "ListActivity";

private ArrayList<Product> productList;
private ListView lvProduct;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    ImageLoader.getInstance().init(UILConfig.config(ListActivity.this));

    PostResponseAsyncTask taskRead = new PostResponseAsyncTask(ListActivity.this, this);
    taskRead.execute("http:///product.php");

}

@Override
public void processFinish(String s) {
    productList = new JsonConverter<Product>().toArrayList(s, Product.class);

    BindDictionary<Product> dict = new BindDictionary<Product>();
    dict.addStringField(R.id.tvName, new StringExtractor<Product>() {
        @Override
        public String getStringValue(Product product, int position) {
            return product.name;
        }
    });


    dict.addStringField(R.id.tvPrice, new StringExtractor<Product>() {
        @Override
        public String getStringValue(Product product, int position) {
            return "" + product.v;
        }
    });
    dict.addDynamicImageField(R.id.ivImage,
            new StringExtractor<Product>() {
                @Override
                public String getStringValue(Product product, int position) {
                    return product.youtubeid;
                }
            }, new DynamicImageLoader() {
                @Override
                public void loadImage(String url, ImageView imageView) {


                    ImageLoader.getInstance().displayImage(url, imageView);
                }
            });

    FunDapter<Product> adapter = new FunDapter<>(
            ListActivity.this, productList, R.layout.layout_list, dict);

    lvProduct = (ListView)findViewById(R.id.lvProduct);
    lvProduct.setAdapter(adapter);
    lvProduct.setOnItemClickListener(this);
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    Product selectedProduct = productList.get(position);
    Intent in = new Intent(ListActivity.this, Detailactivity.class);
    in.putExtra("product", (Serializable) selectedProduct);
    startActivity(in);
}
}