android listview局部刷新和模拟应用下载

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：

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 :zhoujiangbohai@163.com
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：

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 :zhoujiangbohai@163.com
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：

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：

5. 最后创建MainActivity.java，源码：

布局文件activity_main.xml：

<LinearLayoutxmlns:android="http://schemas.android.com/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