124 阿裏雲技術社區[雲棲]

android Listview下拉滾動時自動加載數據

最近在研究網絡數據加載的問題，比如我有幾百，甚至上千條數據，這些數據如果一次性全部加載到arraylist，然後再加載到Listview中。我們必然會去單獨開線程來做，這樣造成的結果就是會出現等待時間很長，用戶體驗非常不好。我的想法是動態加載數據，第一次加載十條，然後往下麵滑動的時候再追加十條，再往下麵滑動的時候再去追加，這樣大大減少了用戶等待的時間，同時給處理數據留下了時間。網上看到了這樣一個例子，挺好的，我改動了一下，達到了我想要的結果。

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AbsListView.OnScrollListener;
import android.widget.LinearLayout.LayoutParams;

public class ListViewForLoading extends Activity implements OnScrollListener {

    private listViewAdapter adapter = new listViewAdapter();
    ListView listView;
    LinearLayout loadingLayout;
    private Thread mThread;
    /**
     * 設置布局顯示屬性
     */
    private LayoutParams mLayoutParams = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    /**
     * 設置布局顯示目標最大化屬性
     */
    private LayoutParams FFlayoutParams = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.FILL_PARENT,
            LinearLayout.LayoutParams.FILL_PARENT);

    private ProgressBar progressBar;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        init();
    }

    private void init() {
        // TODO Auto-generated method stub
        // 線性布局
        LinearLayout layout = new LinearLayout(this);
        // 設置布局 水平方向
        layout.setOrientation(LinearLayout.HORIZONTAL);
        // 進度條
        progressBar = new ProgressBar(this);
        // 進度條顯示位置
        progressBar.setPadding(0, 0, 15, 0);
        // 把進度條加入到layout中
        layout.addView(progressBar, mLayoutParams);
        // 文本內容
        TextView textView = new TextView(this);
        textView.setText("加載中...");
        textView.setGravity(Gravity.CENTER_VERTICAL);
        // 把文本加入到layout中
        layout.addView(textView, FFlayoutParams);
        // 設置layout的重力方向，即對齊方式是
        layout.setGravity(Gravity.CENTER);

        // 設置ListView的頁腳layout
        loadingLayout = new LinearLayout(this);
        loadingLayout.addView(layout, mLayoutParams);
        loadingLayout.setGravity(Gravity.CENTER);

        // 得到一個ListView用來顯示條目
        listView = (ListView) findViewById(R.id.tv);
        // 添加到腳頁顯示
        listView.addFooterView(loadingLayout);
        // 給ListView添加適配器
        listView.setAdapter(adapter);
        // 給ListView注冊滾動監聽
        listView.setOnScrollListener(this);
    }

    /**
     * 要用用於生成顯示數據
     * 
     * @author huangbq
     * 
     */
    class listViewAdapter extends BaseAdapter {
        int count = 10;

        public int getCount() {
            return count;
        }

        public Object getItem(int pos) {
            return pos;
        }

        public long getItemId(int pos) {
            return pos;
        }

        public View getView(int pos, View v, ViewGroup p) {
            TextView view;
            if (v == null) {
                view = new TextView(ListViewForLoading.this);
            } else {
                view = (TextView) v;
            }
            view.setText("ListItem " + pos);
            view.setTextSize(20f);
            view.setGravity(Gravity.CENTER);
            view.setHeight(60);
            return view;
        }
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        // TODO Auto-generated method stub
        if(firstVisibleItem+visibleItemCount==totalItemCount)
        {
            //開線程去下載網絡數據
            if (mThread == null || !mThread.isAlive()) {
                mThread = new Thread() {
                    @Override
                    public void run() {
                        try {
                            //這裏放你網絡數據請求的方法，我在這裏用線程休眠5秒方法來處理
                            Thread.sleep(5000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        Message message = new Message();
                        message.what = 1;
                        handler.sendMessage(message);
                    }
                };
                mThread.start();                
            }
        }
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub        
    }

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            switch (msg.what) {
            case 1:
                if (adapter.count <= 41) {
                    adapter.count += 10;
                    int currentPage = adapter.count / 10;
                    Toast.makeText(getApplicationContext(),"第" + currentPage + "頁", Toast.LENGTH_LONG).show();
                } else {
                    listView.removeFooterView(loadingLayout);
                }
                //重新刷新Listview的adapter裏麵數據
                adapter.notifyDataSetChanged();
                break;
            default:
                break;
            }
        }

    };
}

運行結果如下圖：