在android开发中，listview是比较常用的一个组件，在listview的数据需要更新的时候，一般会用notifyDataSetChanged()这个函数，但是它会更新listview中所有可视范围内的item，这样对性能肯定会有影响。比较常见的情景是android应用商店中的下载列表，当我们下载一款游戏的时候，只需要更新这款游戏对应的进度就可以了。本文就来模拟android应用商店的游戏下载，实现对listview的局部刷新，只实现一个简单的demo，不去真的下载文件。

1. 首先来创建代表应用商店中的app文件的类：AppFile.java，包含了一些基本的属性，源码：

package com.alexzhou.downloadfile; /** * author:alexzhou * email :zhoujiangbohai@163.com * date :2013-1-27 * * 游戏列表中的app文件 **/ public class AppFile {     public int id;    public String name;    // app的大小    public int size;    // 已下载大小    public int downloadSize;    // 下载状态:正常,正在下载，暂停，等待，已下载    public int downloadState;}

2. 由于实际开发时，AppFile的属性比较多，这里创建一个辅助类：DownloadFile.java，代表下载中的文件，源码：

package com.alexzhou.downloadfile; /** * author:alexzhou * email :zhoujiangbohai@163.com * date :2013-1-27 * * 下载的文件 **/ public class DownloadFile {     public int downloadID;    public int downloadSize;    public int totalSize;    public int downloadState;}

3. 接下来需要一个下载管理类：DownloadManager.java，它管理所有下载任务。当同时下载很多任务的时候，界面会卡，所以指定只能同时下载3个任务，每个任务会启动一个线程，这里使用了ExecutorService线程池。当提交了超过三个下载任务时，只执行前3个任务，第四个任务会等到前面有一个下载完成后再下载，以此类推。这里还用到了android提供的一个工具类SparseArray，它是用来替代HashMap的，性能比HashMap要好。下面看源码：

import java.util.ArrayList;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors; import android.os.Handler;import android.os.Message;import android.util.Log;import android.util.SparseArray; /**author:alexzhouemail :zhoujiangbohai@163.comdate  :2013-1-27 下载管理 **/ public class DownloadManager {     // 下载状态：正常，暂停，下载中，已下载，排队中    public static final int DOWNLOAD_STATE_NORMAL = 0x00;    public static final int DOWNLOAD_STATE_PAUSE = 0x01;    public static final int DOWNLOAD_STATE_DOWNLOADING = 0x02;    public static final int DOWNLOAD_STATE_FINISH = 0x03;    public static final int DOWNLOAD_STATE_WAITING = 0x04;     // SparseArray是android中替代Hashmap的类,可以提高效率    private SparseArray
     
       downloadFiles = new SparseArray
      
       ();    // 用来管理所有下载任务    private ArrayList
       
         taskList = new ArrayList
        
         ();    private Handler mHandler;    private final static Object syncObj = new Object();    private static DownloadManager instance;    private ExecutorService executorService;     private DownloadManager()    {        // 最多只能同时下载3个任务，其余的任务排队等待        executorService = Executors.newFixedThreadPool(3);    }     public static DownloadManager getInstance()    {        if(null == instance)        {            synchronized(syncObj) {                instance = new DownloadManager();            }            return instance;        }        return instance;    }     public void setHandler(Handler handler) {        this.mHandler =  handler;    }     // 开始下载，创建一个下载线程    public void startDownload(DownloadFile file) {        downloadFiles.put(file.downloadID, file);        DownloadTask task = new DownloadTask(file.downloadID);        taskList.add(task);        executorService.submit(task);    }     public void stopAllDownloadTask() {        while(taskList.size() != 0)        {            DownloadTask task = taskList.remove(0);            // 可以在这里做其他的处理            task.stopTask();        }        // 会停止正在进行的任务和拒绝接受新的任务        executorService.shutdownNow();     }     // 下载任务    class DownloadTask implements Runnable {         private boolean isWorking = false;        private int downloadId;         public DownloadTask(int id)        {            this.isWorking = true;            this.downloadId = id;        }         public void stopTask()        {            this.isWorking = false;        }         // 更新listview中对应的item        public void update(DownloadFile downloadFile)        {            Message msg = mHandler.obtainMessage();            if(downloadFile.totalSize == downloadFile.downloadSize)                downloadFile.downloadState = DOWNLOAD_STATE_FINISH;            msg.obj = downloadFile;            msg.sendToTarget();         }         public void run() {            // 更新下载文件的状态            DownloadFile downloadFile = downloadFiles.get(downloadId);            downloadFile.downloadState = DOWNLOAD_STATE_DOWNLOADING;            while(isWorking)            {                // 检测是否下载完成                if(downloadFile.downloadState != DOWNLOAD_STATE_DOWNLOADING)                {                    downloadFiles.remove(downloadFile.downloadID);                    taskList.remove(this);                    isWorking = false;                    break;                }                //Log.e("", "downloadSize="+downloadFile.downloadSize+"; size="+downloadFile.totalSize);                // 这里只是模拟了下载，每一秒更新一次item的下载状态                if(downloadFile.downloadSize <= downloadFile.totalSize)                {                    this.update(downloadFile);                }                 if(downloadFile.downloadSize < downloadFile.totalSize)                {                    try {                        Thread.sleep(100);                    } catch (InterruptedException e) {                        e.printStackTrace();                        downloadFile.downloadState = DOWNLOAD_STATE_PAUSE;                        this.update(downloadFile);                        downloadFiles.remove(downloadId);                        isWorking = false;                        break;                    }                     ++ downloadFile.downloadSize;                }            }         }    } }
        
       
      
     

4. 接下来就需要实现listview的adapter了，这里比较重要的一个函数是updateView，这是实现listview局部刷新的关键，通过索引index得到listview中对应位置的子view，然后再更新该view的数据。源码：

package com.alexzhou.downloadfile; import android.content.Context;import android.graphics.drawable.Drawable;import android.os.Handler;import android.os.Message;import android.util.Log;import android.util.SparseArray;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.ListView;import android.widget.TextView; /**author:alexzhouemail :zhoujiangbohai@163.comdate  :2013-1-27 app列表的数据适配器 **/ public class AppListAdapter extends BaseAdapter {     private SparseArray
     
       dataList = null;    private LayoutInflater inflater = null;    private Context mContext;    private DownloadManager downloadManager;    private ListView listView;     public AppListAdapter(Context context, SparseArray
      
        dataList) {        this.inflater = (LayoutInflater) context                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);        this.dataList = dataList;        this.mContext = context;        this.downloadManager = DownloadManager.getInstance();        this.downloadManager.setHandler(mHandler);    }     public void setListView(ListView view)    {        this.listView = view;    }     @Override    public int getCount() {        return dataList.size();    }     @Override    public Object getItem(int position) {        return dataList.get(position);    }     @Override    public long getItemId(int position) {        return position;    }     // 改变下载按钮的样式    private void changeBtnStyle(Button btn, boolean enable)    {        if(enable)        {            btn.setBackgroundResource(R.drawable.btn_download_norm);        }        else        {            btn.setBackgroundResource(R.drawable.btn_download_disable);        }        btn.setEnabled(enable);    }     @Override    public View getView(int position, View convertView, ViewGroup parent) {         final ViewHolder holder;        if (null == convertView) {            holder = new ViewHolder();            convertView = inflater.inflate(R.layout.listitem_app, null);            holder.layout = (LinearLayout) convertView                    .findViewById(R.id.gamelist_item_layout);            holder.icon = (ImageView) convertView                    .findViewById(R.id.app_icon);            holder.name = (TextView) convertView                    .findViewById(R.id.app_name);            holder.size = (TextView) convertView                    .findViewById(R.id.app_size);            holder.btn = (Button) convertView                    .findViewById(R.id.download_btn);            convertView.setTag(holder);        } else {            holder = (ViewHolder) convertView.getTag();        }         // 这里position和app.id的值是相等的        final AppFile app = dataList.get(position);        //Log.e("", "id="+app.id+", name="+app.name);         holder.name.setText(app.name);        holder.size.setText((app.downloadSize * 100.0f / app.size) + "%");         Drawable drawable = mContext.getResources().getDrawable(R.drawable.app_icon);        holder.icon.setImageDrawable(drawable);         switch(app.downloadState)        {        case DownloadManager.DOWNLOAD_STATE_NORMAL:            holder.btn.setText("下载");            this.changeBtnStyle(holder.btn, true);            break;        case DownloadManager.DOWNLOAD_STATE_DOWNLOADING:            holder.btn.setText("下载中");            this.changeBtnStyle(holder.btn, false);            break;        case DownloadManager.DOWNLOAD_STATE_FINISH:            holder.btn.setText("已下载");            this.changeBtnStyle(holder.btn, false);            break;        case DownloadManager.DOWNLOAD_STATE_WAITING:            holder.btn.setText("排队中");            this.changeBtnStyle(holder.btn, false);            break;        }        holder.btn.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                DownloadFile downloadFile = new DownloadFile();                downloadFile.downloadID = app.id;                downloadFile.downloadState = DownloadManager.DOWNLOAD_STATE_WAITING;                app.downloadState = DownloadManager.DOWNLOAD_STATE_WAITING;                downloadFile.downloadSize = app.downloadSize;                downloadFile.totalSize = app.size;                holder.btn.setText("排队中");                changeBtnStyle(holder.btn, false);                downloadManager.startDownload(downloadFile);            }        });        return convertView;    }     static class ViewHolder {        LinearLayout layout;        ImageView icon;        TextView name;        TextView size;        Button btn;    }     private Handler mHandler = new Handler() {         public void handleMessage(Message msg)        {            DownloadFile downloadFile = (DownloadFile)msg.obj;            AppFile appFile = dataList.get(downloadFile.downloadID);            appFile.downloadSize = downloadFile.downloadSize;            appFile.downloadState = downloadFile.downloadState;             // notifyDataSetChanged会执行getView函数，更新所有可视item的数据            //notifyDataSetChanged();            // 只更新指定item的数据，提高了性能            updateView(appFile.id);        }    };     // 更新指定item的数据    private void updateView(int index)    {        int visiblePos = listView.getFirstVisiblePosition();        int offset = index - visiblePos;        //Log.e("", "index="+index+"visiblePos="+visiblePos+"offset="+offset);        // 只有在可见区域才更新        if(offset < 0) return;         View view = listView.getChildAt(offset);        final AppFile app = dataList.get(index);        ViewHolder holder = (ViewHolder)view.getTag();        //Log.e("", "id="+app.id+", name="+app.name);         holder.name.setText(app.name);        holder.size.setText((app.downloadSize * 100.0f / app.size) + "%");        Drawable drawable = mContext.getResources().getDrawable(R.drawable.app_icon);        holder.icon.setImageDrawable(drawable);         switch(app.downloadState)        {        case DownloadManager.DOWNLOAD_STATE_DOWNLOADING:            holder.btn.setText("下载中");            this.changeBtnStyle(holder.btn, false);            break;        case DownloadManager.DOWNLOAD_STATE_FINISH:            holder.btn.setText("已下载");            this.changeBtnStyle(holder.btn, false);            break;        }     }
      
     

3. 接下来需要一个下载管理类：DownloadManager.java，它管理所有下载任务。当同时下载很多任务的时候，界面会卡，所以指定只能同时下载3个任务，每个任务会启动一个线程，这里使用了ExecutorService线程池。当提交了超过三个下载任务时，只执行前3个任务，第四个任务会等到前面有一个下载完成后再下载，以此类推。这里还用到了android提供的一个工具类SparseArray，它是用来替代HashMap的，性能比HashMap要好。下面看源码：

package com.alexzhou.downloadfile; import java.util.ArrayList;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors; import android.os.Handler;import android.os.Message;import android.util.Log;import android.util.SparseArray; /**author:alexzhouemail :zhoujiangbohai@163.comdate  :2013-1-27 下载管理 **/ public class DownloadManager {     // 下载状态：正常，暂停，下载中，已下载，排队中    public static final int DOWNLOAD_STATE_NORMAL = 0x00;    public static final int DOWNLOAD_STATE_PAUSE = 0x01;    public static final int DOWNLOAD_STATE_DOWNLOADING = 0x02;    public static final int DOWNLOAD_STATE_FINISH = 0x03;    public static final int DOWNLOAD_STATE_WAITING = 0x04;     // SparseArray是android中替代Hashmap的类,可以提高效率    private SparseArray
     
       downloadFiles = new SparseArray
      
       ();    // 用来管理所有下载任务    private ArrayList
       
         taskList = new ArrayList
        
         ();    private Handler mHandler;    private final static Object syncObj = new Object();    private static DownloadManager instance;    private ExecutorService executorService;     private DownloadManager()    {        // 最多只能同时下载3个任务，其余的任务排队等待        executorService = Executors.newFixedThreadPool(3);    }     public static DownloadManager getInstance()    {        if(null == instance)        {            synchronized(syncObj) {                instance = new DownloadManager();            }            return instance;        }        return instance;    }     public void setHandler(Handler handler) {        this.mHandler =  handler;    }     // 开始下载，创建一个下载线程    public void startDownload(DownloadFile file) {        downloadFiles.put(file.downloadID, file);        DownloadTask task = new DownloadTask(file.downloadID);        taskList.add(task);        executorService.submit(task);    }     public void stopAllDownloadTask() {        while(taskList.size() != 0)        {            DownloadTask task = taskList.remove(0);            // 可以在这里做其他的处理            task.stopTask();        }        // 会停止正在进行的任务和拒绝接受新的任务        executorService.shutdownNow();     }     // 下载任务    class DownloadTask implements Runnable {         private boolean isWorking = false;        private int downloadId;         public DownloadTask(int id)        {            this.isWorking = true;            this.downloadId = id;        }         public void stopTask()        {            this.isWorking = false;        }         // 更新listview中对应的item        public void update(DownloadFile downloadFile)        {            Message msg = mHandler.obtainMessage();            if(downloadFile.totalSize == downloadFile.downloadSize)                downloadFile.downloadState = DOWNLOAD_STATE_FINISH;            msg.obj = downloadFile;            msg.sendToTarget();         }         public void run() {            // 更新下载文件的状态            DownloadFile downloadFile = downloadFiles.get(downloadId);            downloadFile.downloadState = DOWNLOAD_STATE_DOWNLOADING;            while(isWorking)            {                // 检测是否下载完成                if(downloadFile.downloadState != DOWNLOAD_STATE_DOWNLOADING)                {                    downloadFiles.remove(downloadFile.downloadID);                    taskList.remove(this);                    isWorking = false;                    break;                }                //Log.e("", "downloadSize="+downloadFile.downloadSize+"; size="+downloadFile.totalSize);                // 这里只是模拟了下载，每一秒更新一次item的下载状态                if(downloadFile.downloadSize <= downloadFile.totalSize)                {                    this.update(downloadFile);                }                 if(downloadFile.downloadSize < downloadFile.totalSize)                {                    try {                        Thread.sleep(100);                    } catch (InterruptedException e) {                        e.printStackTrace();                        downloadFile.downloadState = DOWNLOAD_STATE_PAUSE;                        this.update(downloadFile);                        downloadFiles.remove(downloadId);                        isWorking = false;                        break;                    }                     ++ downloadFile.downloadSize;                }            }         }    } }
        
       
      
     

4. 接下来就需要实现listview的adapter了，这里比较重要的一个函数是updateView，这是实现listview局部刷新的关键，通过索引index得到listview中对应位置的子view，然后再更新该view的数据。源码：

package com.alexzhou.downloadfile; import android.content.Context;import android.graphics.drawable.Drawable;import android.os.Handler;import android.os.Message;import android.util.Log;import android.util.SparseArray;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.ListView;import android.widget.TextView; /**author:alexzhouemail :zhoujiangbohai@163.comdate  :2013-1-27 app列表的数据适配器 **/ public class AppListAdapter extends BaseAdapter {     private SparseArray
     
       dataList = null;    private LayoutInflater inflater = null;    private Context mContext;    private DownloadManager downloadManager;    private ListView listView;     public AppListAdapter(Context context, SparseArray
      
        dataList) {        this.inflater = (LayoutInflater) context                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);        this.dataList = dataList;        this.mContext = context;        this.downloadManager = DownloadManager.getInstance();        this.downloadManager.setHandler(mHandler);    }     public void setListView(ListView view)    {        this.listView = view;    }     @Override    public int getCount() {        return dataList.size();    }     @Override    public Object getItem(int position) {        return dataList.get(position);    }     @Override    public long getItemId(int position) {        return position;    }     // 改变下载按钮的样式    private void changeBtnStyle(Button btn, boolean enable)    {        if(enable)        {            btn.setBackgroundResource(R.drawable.btn_download_norm);        }        else        {            btn.setBackgroundResource(R.drawable.btn_download_disable);        }        btn.setEnabled(enable);    }     @Override    public View getView(int position, View convertView, ViewGroup parent) {         final ViewHolder holder;        if (null == convertView) {            holder = new ViewHolder();            convertView = inflater.inflate(R.layout.listitem_app, null);            holder.layout = (LinearLayout) convertView                    .findViewById(R.id.gamelist_item_layout);            holder.icon = (ImageView) convertView                    .findViewById(R.id.app_icon);            holder.name = (TextView) convertView                    .findViewById(R.id.app_name);            holder.size = (TextView) convertView                    .findViewById(R.id.app_size);            holder.btn = (Button) convertView                    .findViewById(R.id.download_btn);            convertView.setTag(holder);        } else {            holder = (ViewHolder) convertView.getTag();        }         // 这里position和app.id的值是相等的        final AppFile app = dataList.get(position);        //Log.e("", "id="+app.id+", name="+app.name);         holder.name.setText(app.name);        holder.size.setText((app.downloadSize * 100.0f / app.size) + "%");         Drawable drawable = mContext.getResources().getDrawable(R.drawable.app_icon);        holder.icon.setImageDrawable(drawable);         switch(app.downloadState)        {        case DownloadManager.DOWNLOAD_STATE_NORMAL:            holder.btn.setText("下载");            this.changeBtnStyle(holder.btn, true);            break;        case DownloadManager.DOWNLOAD_STATE_DOWNLOADING:            holder.btn.setText("下载中");            this.changeBtnStyle(holder.btn, false);            break;        case DownloadManager.DOWNLOAD_STATE_FINISH:            holder.btn.setText("已下载");            this.changeBtnStyle(holder.btn, false);            break;        case DownloadManager.DOWNLOAD_STATE_WAITING:            holder.btn.setText("排队中");            this.changeBtnStyle(holder.btn, false);            break;        }        holder.btn.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                DownloadFile downloadFile = new DownloadFile();                downloadFile.downloadID = app.id;                downloadFile.downloadState = DownloadManager.DOWNLOAD_STATE_WAITING;                app.downloadState = DownloadManager.DOWNLOAD_STATE_WAITING;                downloadFile.downloadSize = app.downloadSize;                downloadFile.totalSize = app.size;                holder.btn.setText("排队中");                changeBtnStyle(holder.btn, false);                downloadManager.startDownload(downloadFile);            }        });        return convertView;    }     static class ViewHolder {        LinearLayout layout;        ImageView icon;        TextView name;        TextView size;        Button btn;    }     private Handler mHandler = new Handler() {         public void handleMessage(Message msg)        {            DownloadFile downloadFile = (DownloadFile)msg.obj;            AppFile appFile = dataList.get(downloadFile.downloadID);            appFile.downloadSize = downloadFile.downloadSize;            appFile.downloadState = downloadFile.downloadState;             // notifyDataSetChanged会执行getView函数，更新所有可视item的数据            //notifyDataSetChanged();            // 只更新指定item的数据，提高了性能            updateView(appFile.id);        }    };     // 更新指定item的数据    private void updateView(int index)    {        int visiblePos = listView.getFirstVisiblePosition();        int offset = index - visiblePos;        //Log.e("", "index="+index+"visiblePos="+visiblePos+"offset="+offset);        // 只有在可见区域才更新        if(offset < 0) return;         View view = listView.getChildAt(offset);        final AppFile app = dataList.get(index);        ViewHolder holder = (ViewHolder)view.getTag();        //Log.e("", "id="+app.id+", name="+app.name);         holder.name.setText(app.name);        holder.size.setText((app.downloadSize * 100.0f / app.size) + "%");        Drawable drawable = mContext.getResources().getDrawable(R.drawable.app_icon);        holder.icon.setImageDrawable(drawable);         switch(app.downloadState)        {        case DownloadManager.DOWNLOAD_STATE_DOWNLOADING:            holder.btn.setText("下载中");            this.changeBtnStyle(holder.btn, false);            break;        case DownloadManager.DOWNLOAD_STATE_FINISH:            holder.btn.setText("已下载");            this.changeBtnStyle(holder.btn, false);            break;        }     }}
      
     

布局文件listitem_app.xml：

listview中item样式文件style_listitem_background.xml：

item中的button样式文件style_btn_download.xml：

字符文件strings.xml

     
         
      
       AndroidDownloadFile
          
      
       下载
      
     

5. 最后创建MainActivity.java，源码：

package com.alexzhou.downloadfile; import android.app.Activity;import android.os.Bundle;import android.util.SparseArray;import android.widget.ListView; public class MainActivity extends Activity{    private SparseArray
     
       appList = new SparseArray
      
       ();     private ListView listView;     @Override    public void onCreate(Bundle savedInstanceState)    {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initData();        initUI();    }     private void initData()    {        for(int i =0; i<20; i++)        {            AppFile app = new AppFile();            app.name = "快玩游戏--" + (i+1);            app.size = 100;            app.id = i;            app.downloadState = DownloadManager.DOWNLOAD_STATE_NORMAL;            app.downloadSize = 0;            appList.put(app.id, app);        }    }     private void initUI()    {        listView = (ListView)this.findViewById(R.id.listview);        AppListAdapter adapter = new AppListAdapter(this, appList);        adapter.setListView(listView);        listView.setAdapter(adapter);    }     @Override    protected void onDestroy() {        super.onDestroy();        DownloadManager.getInstance().stopAllDownloadTask();    } }
      
     

布局文件activity_main.xml：

到此为止，代码部分已经全部完成了，下面来看看最终效果图：

这里对比一下分别使用updateView和notifyDataSetChanged时，有什么不一样，看看打印日志：

(1)使用notifyDataSetChanged时，listview可视范围内的所有子项都更新了。

 (2)使用updateView时，只更新了指定的子项。

实例源码地址：