Android ListView从网络获取图片及文字显示

这一篇说一下如何从网络获取图片以及文本来显示。事实上，一般是先获取Josn或sml数据，然后解释显示。我们先从网上获取xml，然后对其进行解析，最后显示在ListView上。具体步骤：

• 客户端发出请求，获取xml
• 客户端异步解析xml
• ListView将解析完的数据显示
  

      一、Android客户端


(1)xml布局文件

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<?xml version="1.0"encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical">

          

    <ListView

        android:id="@+id/list"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:divider="#b5b5b5"

        android:dividerHeight="1dp"

        android:listSelector="@drawable/list_selector"/>

  

</LinearLayout>

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<?xml version="1.0"encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="wrap_content"

    android:background="@drawable/list_selector"

    android:orientation="horizontal"

    android:padding="5dip">

  

        <!--  ListView最左边的缩略图 -->

        <LinearLayout android:id="@+id/thumbnail"

                android:layout_width="wrap_content"

                android:layout_height="wrap_content"

                android:padding="3dip"              

        android:layout_alignParentLeft="true"

        android:background="@drawable/image_bg"

            android:layout_marginRight="5dip">

          

                <ImageView    

                android:id="@+id/list_image"  

                android:layout_width="50dip"

                android:layout_height="50dip"

                android:src="@drawable/rihanna"/>

          

        </LinearLayout>

      

        <!-- 歌曲名-->

    <TextView

        android:id="@+id/title"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignTop="@+id/thumbnail"

        android:layout_toRightOf="@+id/thumbnail"

        android:text="Rihanna Love the way lie"

        android:textColor="#040404"

        android:typeface="sans"

        android:textSize="15dip"

        android:textStyle="bold"/>

  

        <!-- 歌手名 -->

    <TextView

        android:id="@+id/artist"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:layout_below="@id/title"

        android:textColor="#343434"

        android:textSize="10dip"

        android:layout_marginTop="1dip"

        android:layout_toRightOf="@+id/thumbnail"

        android:text="Just gona stand there and ..."/>

  

        <!-- 歌曲播放时间 -->

    <TextView

        android:id="@+id/duration"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentRight="true"

        android:layout_alignTop="@id/title"

        android:gravity="right"

        android:text="5:45"

        android:layout_marginRight="5dip"

        android:textSize="10dip"

        android:textColor="#10bcc9"

        android:textStyle="bold"/>

        

     <!-- 进入播放 -->   

     <ImageView android:layout_width="wrap_content"

             android:layout_height="wrap_content"

             android:src="@drawable/arrow"

             android:layout_alignParentRight="true"

             android:layout_centerVertical="true"/>

  

</RelativeLayout>

另外我们打算使用几个特效，一个是当点击列表项目的时候，项目背景色改变，其实就是一个selector；另一个就是用shape美化视觉效果，具体看xml代码：

1.list_selector.xml

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<?xml version="1.0"encoding="utf-8"?>

<selector xmlns:android="http://schemas.android.com/apk/res/android">

<!-- Selector styleforlistrow -->

<item

 android:state_selected="false"

    android:state_pressed="false"

    android:drawable="@drawable/gradient_bg"/>

<item android:state_pressed="true"

    android:drawable="@drawable/gradient_bg_hover"/>

<item android:state_selected="true"

 android:state_pressed="false"

    android:drawable="@drawable/gradient_bg_hover"/>

</selector>

     

2.gradient_bg.xml，是默认背景梯度风格

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<?xml version="1.0"encoding="utf-8"?>

<shape xmlns:android="http://schemas.android.com/apk/res/android"

    android:shape="rectangle">

  <!--  Gradient Bgforlistrow -->

  <gradient

      android:startColor="#f1f1f2"

      android:centerColor="#e7e7e8"

      android:endColor="#cfcfcf"

      android:angle="270"/>

</shape>

3.gradient_bg_hover.xml 梯度风格在悬停状态

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<?xml version="1.0"encoding="utf-8"?>

<shape xmlns:android="http://schemas.android.com/apk/res/android"

    android:shape="rectangle">

  <!-- Gradient BgColorforlistrow Selected -->

  <gradient

      android:startColor="#18d7e5"

      android:centerColor="#16cedb"

      android:endColor="#09adb9"

      android:angle="270"/>

    

</shape>

4.image_bg.xml 在图片周围的白色边条

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<?xml version="1.0"encoding="utf-8"?>

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">

    <item>

      <shape

        android:shape="rectangle">

            <stroke android:width="1dp"android:color="#dbdbdc"/>

            <solid android:color="#FFFFFF"/>

        </shape>

   </item>

</layer-list>

以上效果基本上都用到了shape，对此不了解的可以去查看相关资料。上面就是全部的xml布局文件，下面将开始写代码。



(2)主要代码

代码部分主要涉及到一下几个功能，重写ListView的适配器（BaseAdapter），从网络获取图片，图片缓存的处理，xml的解析。
①重写ListView的适配器，这部分可以参考上一篇文章，LazyAdapter.java   

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import java.util.ArrayList;

import java.util.HashMap;

import android.app.Activity;

import android.content.Context;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.BaseAdapter;

import android.widget.ImageView;

import android.widget.TextView;

  

public class LazyAdapter extendsBaseAdapter {

      

    privateActivity activity;

    privateArrayList<HashMap<String, String>> data;

    privatestaticLayoutInflater inflater=null;

    publicImageLoader imageLoader;//用来下载图片的类，后面有介绍

      

    publicLazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {

        activity = a;

        data=d;

        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        imageLoader=newImageLoader(activity.getApplicationContext());

    }

  

    publicintgetCount() {

        returndata.size();

    }

  

    publicObject getItem(intposition) {

        returnposition;

    }

  

    publiclonggetItemId(intposition) {

        returnposition;

    }

      

    publicView getView(intposition, View convertView, ViewGroup parent) {

        View vi=convertView;

        if(convertView==null)

            vi = inflater.inflate(R.layout.list_row,null);

  

        TextView title = (TextView)vi.findViewById(R.id.title);// 标题

        TextView artist = (TextView)vi.findViewById(R.id.artist);// 歌手名

        TextView duration = (TextView)vi.findViewById(R.id.duration);// 时长

        ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image);// 缩略图

          

        HashMap<String, String> song =newHashMap<String, String>();

        song = data.get(position);

          

        // 设置ListView的相关值

        title.setText(song.get(CustomizedListView.KEY_TITLE));

        artist.setText(song.get(CustomizedListView.KEY_ARTIST));

        duration.setText(song.get(CustomizedListView.KEY_DURATION));

        imageLoader.DisplayImage(song.get(CustomizedListView.KEY_THUMB_URL), thumb_image);

        returnvi;

  <EM>  }

}</EM>

②网络获取图片的类，ImageLoader.java：   

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import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.InputStream;

import java.io.OutputStream;

import java.net.HttpURLConnection;

import java.net.URL;

import java.util.Collections;

import java.util.Map;

import java.util.WeakHashMap;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors; 

import android.app.Activity;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.widget.ImageView;

    

public class ImageLoader {

    

    MemoryCache memoryCache=newMemoryCache();

    FileCache fileCache;

    privateMap<ImageView, String> imageViews=Collections.synchronizedMap(newWeakHashMap<ImageView, String>());

    ExecutorService executorService; 

    

    publicImageLoader(Context context){

        fileCache=newFileCache(context);

        executorService=Executors.newFixedThreadPool(5);

    }

    

    finalintstub_id = R.drawable.no_image;

    publicvoidDisplayImage(String url, ImageView imageView)

    {

        imageViews.put(imageView, url);

        Bitmap bitmap=memoryCache.get(url);

        if(bitmap!=null)

            imageView.setImageBitmap(bitmap);

        else

        {

            queuePhoto(url, imageView);

            imageView.setImageResource(stub_id);

        }

    }

    

    privatevoidqueuePhoto(String url, ImageView imageView)

    {

        PhotoToLoad p=newPhotoToLoad(url, imageView);

        executorService.submit(newPhotosLoader(p));

    }

    

    privateBitmap getBitmap(String url)

    {

        File f=fileCache.getFile(url);

    

        //从sd卡

        Bitmap b = decodeFile(f);

        if(b!=null)

            returnb;

    

        //从网络

        try{

            Bitmap bitmap=null;

            URL imageUrl =newURL(url);

            HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();

            conn.setConnectTimeout(30000);

            conn.setReadTimeout(30000);

            conn.setInstanceFollowRedirects(true);

            InputStream is=conn.getInputStream();

            OutputStream os =newFileOutputStream(f);

            Utils.CopyStream(is, os);

            os.close();

            bitmap = decodeFile(f);

            returnbitmap;

        }catch(Exception ex){

           ex.printStackTrace();

           returnnull;

        }

    }

    

    //解码图像用来减少内存消耗

    privateBitmap decodeFile(File f){

        try{

            //解码图像大小

            BitmapFactory.Options o =newBitmapFactory.Options();

            o.inJustDecodeBounds =true;

            BitmapFactory.decodeStream(newFileInputStream(f),null,o);

    

            //找到正确的刻度值，它应该是2的幂。

            finalintREQUIRED_SIZE=70;

            intwidth_tmp=o.outWidth, height_tmp=o.outHeight;

            intscale=1;

            while(true){

                if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)

                    break;

                width_tmp/=2;

                height_tmp/=2;

                scale*=2;

            }

    

            BitmapFactory.Options o2 =newBitmapFactory.Options();

            o2.inSampleSize=scale;

            returnBitmapFactory.decodeStream(newFileInputStream(f),null, o2);

        }catch(FileNotFoundException e) {}

        returnnull;

    }

    

    /任务队列

    privateclassPhotoToLoad

    {

        publicString url;

        publicImageView imageView;

        publicPhotoToLoad(String u, ImageView i){

            url=u;

            imageView=i;

        }

    }

    

    classPhotosLoaderimplementsRunnable {

        PhotoToLoad photoToLoad;

        PhotosLoader(PhotoToLoad photoToLoad){

            this.photoToLoad=photoToLoad;

        }

    

        @Override

        publicvoidrun() {

            if(imageViewReused(photoToLoad))

                return;

            Bitmap bmp=getBitmap(photoToLoad.url);

            memoryCache.put(photoToLoad.url, bmp);

            if(imageViewReused(photoToLoad))

                return;

            BitmapDisplayer bd=newBitmapDisplayer(bmp, photoToLoad);

            Activity a=(Activity)photoToLoad.imageView.getContext();

            a.runOnUiThread(bd);

        }

    }

    

    booleanimageViewReused(PhotoToLoad photoToLoad){

        String tag=imageViews.get(photoToLoad.imageView);

        if(tag==null|| !tag.equals(photoToLoad.url))

            returntrue;

        returnfalse;

    }

    

    //用于显示位图在UI线程

    classBitmapDisplayerimplementsRunnable

    {

        Bitmap bitmap;

        PhotoToLoad photoToLoad;

        publicBitmapDisplayer(Bitmap b, PhotoToLoad p){bitmap=b;photoToLoad=p;}

        publicvoidrun()

        {

            if(imageViewReused(photoToLoad))

                return;

            if(bitmap!=null)

                photoToLoad.imageView.setImageBitmap(bitmap);

            else

                photoToLoad.imageView.setImageResource(stub_id);

        }

    }

    

    publicvoidclearCache() {

        memoryCache.clear();

        fileCache.clear();

    }

    

}

③xml解析，xml的解析有很多方法，这里采用进行dom方式的xml解析。

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import java.io.IOException;

import java.io.StringReader;

import java.io.UnsupportedEncodingException;  

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;  

import org.apache.http.HttpEntity;

import org.apache.http.HttpResponse;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.methods.HttpPost;

import org.apache.http.impl.client.DefaultHttpClient;

import org.apache.http.util.EntityUtils;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException; 

import android.util.Log;

    

public class XMLParser {

    

    // 构造方法

    publicXMLParser() {

    

    }

    

    /**

     * 从URL获取XML使HTTP请求

     * @param url string

     * */

    publicString getXmlFromUrl(String url) {

        String xml =null;

    

        try{

            // defaultHttpClient

            DefaultHttpClient httpClient =newDefaultHttpClient();

            HttpPost httpPost =newHttpPost(url);

    

            HttpResponse httpResponse = httpClient.execute(httpPost);

            HttpEntity httpEntity = httpResponse.getEntity();

            xml = EntityUtils.toString(httpEntity);

    

        }catch(UnsupportedEncodingException e) {

            e.printStackTrace();

        }catch(ClientProtocolException e) {

            e.printStackTrace();

        }catch(IOException e) {

            e.printStackTrace();

        }

        returnxml;

    }

    

    /**

     * 获取XML DOM元素

     * @param XML string

     * */

    publicDocument getDomElement(String xml){

        Document doc =null;

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();

        try{

    

            DocumentBuilder db = dbf.newDocumentBuilder();

    

            InputSource is =newInputSource();

                is.setCharacterStream(newStringReader(xml));

                doc = db.parse(is); 

    

            }catch(ParserConfigurationException e) {

                Log.e("Error: ", e.getMessage());

                returnnull;

            }catch(SAXException e) {

                Log.e("Error: ", e.getMessage());

                returnnull;

            }catch(IOException e) {

                Log.e("Error: ", e.getMessage());

                returnnull;

            }

    

            returndoc;

    }

    

    /** 获取节点值

      * @param elem element

      */

     publicfinalString getElementValue( Node elem ) {

         Node child;

         if( elem !=null){

             if(elem.hasChildNodes()){

                 for( child = elem.getFirstChild(); child !=null; child = child.getNextSibling() ){

                     if( child.getNodeType() == Node.TEXT_NODE  ){

                         returnchild.getNodeValue();

                     }

                 }

             }

         }

         return"";

     }

    

     /**

      * 获取节点值

      * @param Element node

      * @param key string

      * */

     publicString getValue(Element item, String str) {

            NodeList n = item.getElementsByTagName(str);

            returnthis.getElementValue(n.item(0));

        }

}

④程序缓存的处理，主要是内存缓存+文件缓存。内存缓存中网上很多是采用SoftReference来防止堆溢出：

MemoryCache.java：

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import java.lang.ref.SoftReference;

import java.util.Collections;

import java.util.HashMap;

import java.util.Map;

import android.graphics.Bitmap;

  

public class MemoryCache {

    privateMap<String, SoftReference<Bitmap>> cache=Collections.synchronizedMap(newHashMap<String, SoftReference<Bitmap>>());//软引用

      

    publicBitmap get(String id){

        if(!cache.containsKey(id))

            returnnull;

        SoftReference<Bitmap> ref=cache.get(id);

        returnref.get();

    }

      

    publicvoidput(String id, Bitmap bitmap){

        cache.put(id,newSoftReference<Bitmap>(bitmap));

    }

  

    publicvoidclear() {

        cache.clear();

    }

}

FileCache.java

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import java.io.File;

import android.content.Context;

  

public class FileCache {

      

    privateFile cacheDir;

      

    publicFileCache(Context context){

        //找一个用来缓存图片的路径

        if(android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))

            cacheDir=newFile(android.os.Environment.getExternalStorageDirectory(),"LazyList");

        else

            cacheDir=context.getCacheDir();

        if(!cacheDir.exists())

            cacheDir.mkdirs();

    }

      

    publicFile getFile(String url){

          

        String filename=String.valueOf(url.hashCode());

        File f =newFile(cacheDir, filename);

        returnf;

          

    }

      

    publicvoidclear(){

        File[] files=cacheDir.listFiles();

        if(files==null)

            return;

        for(File f:files)

            f.delete();

    }

  

}

⑤还有一个读取流的工具类，Utils.java：

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import java.io.InputStream;

import java.io.OutputStream;

  

  

public class Utils {

public static void CopyStream(InputStream is, OutputStream os)

 {

final int buffer_size=1024;

try

 {

byte[] bytes=newbyte[buffer_size];

 for(;;)

 {

 intcount=is.read(bytes,0, buffer_size);

if(count==-1)

break;

os.write(bytes, 0, count);

is.close();

os.close();

 }

}

catch(Exception ex){}

 }

}

还可以像下面这样表达，方法是一样的，就是表达形式上不同：

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public static byte[] readStream(InputStream inStream)throwsException{

  

ByteArrayOutputStream outSteam =newByteArrayOutputStream();

byte[] buffer =newbyte[1024];

int len = -1;

while( (len=inStream.read(buffer)) != -1){

outSteam.write(buffer,0, len);

  

}

outSteam.close();

inStream.close();

return outSteam.toByteArray();

  

}

}

最后就是主Activity的代码了，

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package com.example.androidhive;

  

import java.util.ArrayList;

import java.util.HashMap;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.NodeList;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.AdapterView;

import android.widget.AdapterView.OnItemClickListener;

import android.widget.ListView;

  

public class CustomizedListView extendsActivity {

        // 所有的静态变量

        staticfinalString URL = "http://api.androidhive.info/music/music.xml";//xml目的地址,打开地址看一下

        // XML 节点

        staticfinalString KEY_SONG ="song";// parent node

        staticfinalString KEY_ID = "id";

        staticfinalString KEY_TITLE ="title";

        staticfinalString KEY_ARTIST ="artist";

        staticfinalString KEY_DURATION ="duration";

        staticfinalString KEY_THUMB_URL ="thumb_url";

          

        ListView list;

        LazyAdapter adapter;

  

        @Override

        publicvoidonCreate(Bundle savedInstanceState) {

                super.onCreate(savedInstanceState);

                setContentView(R.layout.main);

                  

  

                ArrayList<HashMap<String, String>> songsList =newArrayList<HashMap<String, String>>();

  

                XMLParser parser =newXMLParser();

                String xml = parser.getXmlFromUrl(URL);// 从网络获取xml

                Document doc = parser.getDomElement(xml);// 获取 DOM 节点

                  

                NodeList nl = doc.getElementsByTagName(KEY_SONG);

                // 循环遍历所有的歌节点 <song>

                for(inti = 0; i < nl.getLength(); i++) {

                        // 新建一个 HashMap

                        HashMap<String, String> map =newHashMap<String, String>();

                        Element e = (Element) nl.item(i);

                        //每个子节点添加到HashMap关键= >值

                        map.put(KEY_ID, parser.getValue(e, KEY_ID));

                        map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));

                        map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));

                        map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));

                        map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));

  

                        // HashList添加到数组列表

                        songsList.add(map);

                }

                  

  

                list=(ListView)findViewById(R.id.list);

                  

                  

              adapter=newLazyAdapter(this, songsList);       

              list.setAdapter(adapter);

          

  

        //为单一列表行添加单击事件

  

        list.setOnItemClickListener(newOnItemClickListener() {

  

                        @Override

                        publicvoidonItemClick(AdapterView<?> parent, View view,

                                        intposition,long id) {

                                                          

                        //这里可以自由发挥，比如播放一首歌曲等等

                        }

                });               

        }       

}

最后看一下效果：