动态增加列表视图中的元素数量

我想增加列表视图滚动到末尾时动态显示的项目数量。 就我而言，我的列表视图最初将显示 10 个项目。然后，当我们滚动到最后一个项目时，它必须开始显示另外 10 个项目，依此类推。 我怎样才能做到这一点？？

这是我的自定义阵列适配器

    package com.android.listview;

import java.util.ArrayList;

import com.android.listview.R;
import com.android.listview.Product;

import android.widget.ArrayAdapter;

import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import com.android.listview.ListViewActivity;

public class CustomArrayAdapter extends ArrayAdapter<Product> implements
        OnScrollListener {

    private final Context context;
    private final ArrayList<Product> values;

    static class ViewHolder {
        public TextView text;
        public ImageView image;
    }

    public CustomArrayAdapter(Context arg0, int arg1, int arg2,
            ArrayList<Product> arg3) {
        super(arg0, arg1, arg2, arg3);
        this.context = arg0;
        this.values = arg3;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        int product_id = 0;
        View rowView = inflater.inflate(R.layout.feed_items, parent, false);
        try {

            ImageView wic_logo = (ImageView) rowView.findViewById(R.id.logo);
            TextView label = (TextView) rowView.findViewById(R.id.label);

            Product p = values.get(position);
            product_id = p.productId;
            String date = new java.text.SimpleDateFormat("dd/MM/yy")
                    .format(new java.util.Date(p.timeStamp));
            label.setText(p.productName + "\n" + p.reportedPrice + "   MRP: "
                    + p.mrp + "\n" + "Discount: " + p.discount + "%   "
                    + p.area + "  " + p.city + "\n" + "Shared by " + p.userName
                    + " " + "on" + " " + date);

            wic_logo.setImageResource(R.drawable.wic_logo_small);
            Log.d("date", "" + date);

            Log.d("Custom Array Adapter", "at" + position);
        } catch (Exception e) {
            Log.d("Custom Array Adapter", "catch");
        }

        return rowView;
    }

    public void onScroll(AbsListView arg0, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        Log.d("entered onScroll", " " + firstVisibleItem + visibleItemCount
                + totalItemCount);
        if (((firstVisibleItem + visibleItemCount) >= totalItemCount - 1)) {
            Log.d("entered if", " " + firstVisibleItem + visibleItemCount
                    + totalItemCount);
            // if we're at the bottom of the listview, load more data
            addData(totalItemCount, values.get(totalItemCount).productId);
        }
    }

    private void addData(int totalItemCount, int productId) {

        Toast.makeText(getContext(), "last item", Toast.LENGTH_SHORT).show();
    }

    public void onScrollStateChanged(AbsListView arg0, int arg1) {

    }
}

这是我的活动

package com.android.listview;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import com.android.listview.CustomArrayAdapter;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.Button;
import android.widget.ListView;

public class ListViewActivity extends Activity {

    static Product[] feed_products_list;
    private JSONArray JArray;
    private InputStream is;
    private StringBuilder sb;
    private String result;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button feed_button = (Button) findViewById(R.id.feedButton_feed);
        feed_button.setBackgroundResource(R.color.grey);
        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
        try {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost("http://10.0.2.2/wic2/mobile/feed");
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            ResponseHandler<String> responseHandler = new BasicResponseHandler();
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();

            try {
                BufferedReader reader = new BufferedReader(
                        new InputStreamReader(is, "iso-8859-1"), 8);
                sb = new StringBuilder();
                sb.append(reader.readLine() + "\n");
                String line = "0";
                while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
                }
                is.close();
                result = sb.toString();
                Log.d("result", result);
            } catch (Exception e) {
                Log.e("error", "Error in http connection" + e.toString());
            }

            Log.e("response", "response is:" + response.toString());
        } catch (Exception e) {
            Log.e("error", "Error in http connection" + e.toString());
        }

        ListView tv = (ListView) findViewById(R.id.feedListView);
        try {
            Log.d("JArray", "entered try");
            JArray = new JSONArray(result);
            int length = JArray.length();
            feed_products_list = new Product[length+1];
            Log.d("JArray", "try last line");
        } catch (JSONException e) {
            Log.d("JArray", "in catch");
            e.printStackTrace();
        }

        JSONObject jsonObj;

        for (int i = 0; i < JArray.length(); i++) {
            try {
                Log.d("jsonObj", "entered try");
                jsonObj = JArray.getJSONObject(i);
            } catch (Exception e) {
                Log.d("jsonObj", "in catch");
                continue;
            }

            try {
                Log.d("feed_products_list", "entered try");
                feed_products_list[i] = new Product(jsonObj.getInt("id"),
                        jsonObj.getString("image"),
                        jsonObj.getString("product_name"),
                        jsonObj.getString("reported_price_formated"),
                        jsonObj.getString("store_area"),
                        jsonObj.getString("store_city"),
                        jsonObj.getString("mrp"),
                        jsonObj.getString("user_name"),
                        jsonObj.getLong("reported_timestamp"),
                        jsonObj.getInt("discount"));
                Log.d("feed_products_list", feed_products_list[i].productName);
            } catch (JSONException e) {
                Log.d("feed_products_list in catch",
                        feed_products_list[i].productName);
                e.printStackTrace();
            }
        }

        tv.setAdapter(new CustomArrayAdapter(this, R.layout.feed_items,
                R.id.label, feed_products_list));


    }
}

还有一个问题是我必须使用 JArray 中的项目数初始化数组 feed_products_list[length] 。所以我每次滚动到最后一项并再次重新填充整个列表时都无法更改数组大小

首先，您的代码存在一些问题。在你的Activity，改变你的变量values to an ArrayList<Product>因为创建后无法操纵数组的长度。接下来，将 JArray 重命名为 jArray；如果第一个字母是大写，则表明您正在处理一个类而不是一个变量。

此外，您没有使用 ViewHolder 模式，这极大地提高了性能。查看vogella.com 上有关 ListView 的链接 http://www.vogella.com/articles/AndroidListView/article.html;进一步来说，查看第 3.1 和 3.2 章.

In CustomArrayAdapter， 实施OnScrollListener并添加所需的方法。然后，在onScroll(...)，确定是否要添加数据（例如用户到达列表底部）。最后，加载新项目，将它们添加到您的数据集中values.add(product) or values.addAll(products)其中产品是List of Products，并调用notifyDataSetChanged从你的内心CustomArrayAdapter每次致电后values.add(...) or values.addAll(...).

例如，您可以在代码中更改以下内容：

In your Activity:

• 删除线条

  int length = JArray.length();
  feed_products_list = new Product[length+1];
  

• 消除你的“静电”feed_products_list并将其更改为 ArrayList：

  private ArrayList<Product> feed_products_list = new ArrayList<Product>();
  

• 代替feed_products_list[i] = new Product(jsonObj.getInt("id"), .... yadiya ...，调用 feed_products_list.add(new Product(jsonObj.getInt("id"), ... yadiya ...`。

In your Adapter:

• 上课implement OnScrollListener，并设置onScroll()- 类似以下的方法：

  public void onScroll(AbsListView view, int firstVisibleItem,
                          int visibleItemCount, final int totalItemCount) {
      if(((firstVisibleItem + visibleItemCount) >= totalItemCount)) {
  
          // if we're at the bottom of the listview, load more data
          addData(totalItemCount);
      }
  }
  

• 创建一个方法addData(long offset):

  private void addData(long offset) {
  
      // download your data, pass the offset so you know where to start
      // and when you convert your json into `Product`s
      Product product = new Product(JSONObject.getInt("id"), ... yadiya ...);
      this.add(product);
      this.notifyDataSetChanged();
  
      // make sure to call notifyDataSetChanged() on your UI-Thread.
  }