android listview局部刷新和模拟应用下载 | Alex Zhou的程序世界

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：

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package com.alexzhou.downloadfile; /**  * author:alexzhou  * email :[e-mail]  * 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：

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package com.alexzhou.downloadfile; /**  * author:alexzhou  * email :[e-mail]  * 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：

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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:alexzhou email :[e-mail] date  :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<DownloadFile> downloadFiles = new SparseArray<DownloadFile>();     // 用来管理所有下载任务     private ArrayList<DownloadTask> taskList = new ArrayList<DownloadTask>();     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：

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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:alexzhou email :[e-mail] date  :2013-1-27 app列表的数据适配器  **/ public class AppListAdapter extends BaseAdapter {     private SparseArray<AppFile> dataList = null;     private LayoutInflater inflater = null;     private Context mContext;     private DownloadManager downloadManager;     private ListView listView;     public AppListAdapter(Context context, SparseArray<AppFile> 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：

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<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas./apk/res/android"     android:id="@+id/gamelist_item_layout"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:gravity="center_vertical"     android:background="@drawable/style_listitem_background"     android:paddingBottom="5dp"     android:paddingTop="5dp" >     <ImageView         android:id="@+id/app_icon"         android:layout_width="53dip"         android:layout_height="53dip"         android:layout_marginLeft="5dip"         android:adjustViewBounds="false"         android:padding="5dp" />     <LinearLayout         android:layout_width="match_parent"         android:layout_height="60dp"         android:layout_marginLeft="5dp"         android:layout_weight="1"         android:gravity="center_vertical"         android:orientation="vertical" >         <TextView             android:id="@+id/app_name"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:singleLine="true"             android:text=""             android:textColor="#000000"             android:textSize="13sp" />         <TextView             android:id="@+id/app_size"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:textColor="#000000"             android:textSize="10sp" />     </LinearLayout>     <Button         android:id="@+id/download_btn"         android:layout_width="55dip"         android:layout_height="30dip"         android:layout_marginRight="10dip"         android:background="@drawable/style_btn_download"         android:focusable="false"         android:text="@string/download"         android:textColor="#ffffffff"         android:textSize="12sp" /> </LinearLayout>

listview中item样式文件style_listitem_background.xml：

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<?xml version="1.0" encoding="utf-8"?> <selector xmlns:android="http://schemas./apk/res/android">    <!-- 没有焦点时的背景颜色 -->   <item android:state_window_focused="false"  >       <shape>          <gradient              android:startColor="#ffffff"              android:endColor="#E3E3E3"              android:angle="-90" />        </shape>   </item>    <!-- 非触摸模式下获得焦点并单击时的背景颜色 -->       <item android:state_focused="true" android:state_pressed="true"         android:drawable="@drawable/bg_listview_item_selected" />    <!--触摸模式下单击时的背景颜色  -->   <item android:state_focused="false" android:state_pressed="true"         android:drawable="@drawable/bg_listview_item_selected" />    <!--选中时的背景颜色  -->   <item android:state_selected="true"  android:drawable="@drawable/bg_listview_item_selected" />   <!--获得焦点时的背景  颜色-->   <item android:state_focused="true" android:drawable="@drawable/bg_listview_item_selected" /> </selector>

item中的button样式文件style_btn_download.xml：

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<?xml version="1.0" encoding="utf-8"?> <selector xmlns:android="http://schemas./apk/res/android">     <item android:state_pressed="true"         android:drawable="@drawable/btn_download_pressed" />     <item android:drawable="@drawable/btn_download_norm" /> </selector>

字符文件strings.xml：

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<?xml version="1.0" encoding="utf-8"?> <resources>     <string name="app_name">AndroidDownloadFile</string>     <string name="download">下载</string> </resources>

5. 最后创建MainActivity.java，源码：

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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<AppFile> appList = new SparseArray<AppFile>();     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：

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<LinearLayout xmlns:android="http://schemas./apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ListView android:id="@+id/listview" android:layout_width="fill_parent" android:layout_height="fill_parent" android:fastScrollEnabled="true" /> </LinearLayout>

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：http://pan.baidu.com/share/link?shareid=229182&uk=167811495,