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:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/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:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/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:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/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:

<?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:

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:

<LinearLayout xmlns: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,

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9 条评论

  1. 楼主你好,请问您这个所下载的文件的网址为什么没有体现出来?

  2. 楼主,我照你做的。为什么进度条更新会出现混乱的情况!

  3. kidy :
    楼上,空指针的错误怎么解决的?

    同问…..空指针不知道怎么解决,郁闷…

  4. 弱弱地问一句,下载中的状态,向上滑的时候,会在这句报空指针:ViewHolder holder = (ViewHolder)view.getTag();有什么办法解决这个bug么

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