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  • 【转】异步加载图片，使用LruCache和SD卡或手机缓存，效果非常的流畅

    From:http://blog.csdn.net/xiaanming/article/details/9825113

    文中的LruCache是非常好的内存缓存管理工具，代替软引用的首选。

    异步加载图片的例子，网上也比较多，大部分用了HashMap<String, SoftReference<Drawable>> imageCache ，但是现在已经不再推荐使用这种方式了，因为从 Android 2.3 (API Level 9)开始，垃圾回收器会更倾向于回收持有软引用或弱引用的对象，这让软引用和弱引用变得不再可靠。另外，Android 3.0 (API Level 11)中，图片的数据会存储在本地的内存当中，因而无法用一种可预见的方式将其释放，这就有潜在的风险造成应用程序的内存溢出并崩溃，所以我这里用得是LruCache来缓存图片，当存储Image的大小大于LruCache设定的值，系统自动释放内存，这个类是3.1版本中提供的，如果你是在更早的Android版本中开发，则需要导入android-support-v4的jar包（这里要注意咯）


    为什么写这篇文章呢？

    因为我之前做的项目中，也有异步加载图片，那时候用得是Thread去下载图片，每次下载图片都要new Thread去下载，而且还是并发去下载，每次都new 一个线程浪费内存，老板说服务器承受不起这么多的连接，叫我改成先获取一张图片之后再去获取下一张，这样子保存与服务器的连接为一个，服务器压力小了，然后楼主就想到线程池，线程池很好的帮我们管理并发的问题，并发的问题解决了，可是后面又出问题了，图片多了就出现OOM(OutOfMemory)异常，之后用了SoftReference，先用SoftReference中获取图片，SoftReference没有就开线程去下载，老板说你为什么不把图片在手机上做个缓存呢，于是我用了手机缓存，大概思路就是先从SoftReference中获取图片，如果SoftReference没有就去手机缓存中获取，手机缓存中没有就开启先从去下载，然后成功的解决了OOM的问题，前些天老板要我重构下代码，我也觉得之前写的代码耦合性太强，早就想改，然后之前看到guolin的Android照片墙应用实现，再多的图片也不怕崩溃的这篇文章，LruCache和滑动过程中取消下载任务，停下来的时候才去下载这2点比较好，值得我学习，然后我就将我的项目异步加载这一块改了下，发到这里做个记录吧，以后类似的异步加载图片直接拷贝代码，提交开发的效率

     

    这篇文章做了哪些方面的优化

    1. 使用了线程池来管理下载任务
    2. 使用LruCache来缓存图片
    3. 使用手机来缓存图片
    4. GridView滑动的时候取消下载任务，静止的时候进行下载，GridView滑动更加的流畅
    5. 降低了代码的耦合性，结构更加的清晰，便于以后重用

    接下来我们先来看看项目的结构

    • FileUtils 文件操作的工具类，提供保存图片，获取图片，判断图片是否存在，删除图片的一些方法，这个类比较简单
    [java] view plaincopy
     
    1. package com.example.asyncimageloader;  
    2.   
    3. import java.io.File;  
    4. import java.io.FileOutputStream;  
    5. import java.io.IOException;  
    6.   
    7. import android.content.Context;  
    8. import android.graphics.Bitmap;  
    9. import android.graphics.Bitmap.CompressFormat;  
    10. import android.graphics.BitmapFactory;  
    11. import android.os.Environment;  
    12.   
    13. public class FileUtils {  
    14.     /** 
    15.      * sd卡的根目录 
    16.      */  
    17.     private static String mSdRootPath = Environment.getExternalStorageDirectory().getPath();  
    18.     /** 
    19.      * 手机的缓存根目录 
    20.      */  
    21.     private static String mDataRootPath = null;  
    22.     /** 
    23.      * 保存Image的目录名 
    24.      */  
    25.     private final static String FOLDER_NAME = "/AndroidImage";  
    26.       
    27.       
    28.     public FileUtils(Context context){  
    29.         mDataRootPath = context.getCacheDir().getPath();  
    30.     }  
    31.       
    32.   
    33.     /** 
    34.      * 获取储存Image的目录 
    35.      * @return 
    36.      */  
    37.     private String getStorageDirectory(){  
    38.         return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ?  
    39.                 mSdRootPath + FOLDER_NAME : mDataRootPath + FOLDER_NAME;  
    40.     }  
    41.       
    42.     /** 
    43.      * 保存Image的方法，有sd卡存储到sd卡，没有就存储到手机目录 
    44.      * @param fileName  
    45.      * @param bitmap    
    46.      * @throws IOException 
    47.      */  
    48.     public void savaBitmap(String fileName, Bitmap bitmap) throws IOException{  
    49.         if(bitmap == null){  
    50.             return;  
    51.         }  
    52.         String path = getStorageDirectory();  
    53.         File folderFile = new File(path);  
    54.         if(!folderFile.exists()){  
    55.             folderFile.mkdir();  
    56.         }  
    57.         File file = new File(path + File.separator + fileName);  
    58.         file.createNewFile();  
    59.         FileOutputStream fos = new FileOutputStream(file);  
    60.         bitmap.compress(CompressFormat.JPEG, 100, fos);  
    61.         fos.flush();  
    62.         fos.close();  
    63.     }  
    64.       
    65.     /** 
    66.      * 从手机或者sd卡获取Bitmap 
    67.      * @param fileName 
    68.      * @return 
    69.      */  
    70.     public Bitmap getBitmap(String fileName){  
    71.         return BitmapFactory.decodeFile(getStorageDirectory() + File.separator + fileName);  
    72.     }  
    73.       
    74.     /** 
    75.      * 判断文件是否存在 
    76.      * @param fileName 
    77.      * @return 
    78.      */  
    79.     public boolean isFileExists(String fileName){  
    80.         return new File(getStorageDirectory() + File.separator + fileName).exists();  
    81.     }  
    82.       
    83.     /** 
    84.      * 获取文件的大小 
    85.      * @param fileName 
    86.      * @return 
    87.      */  
    88.     public long getFileSize(String fileName) {  
    89.         return new File(getStorageDirectory() + File.separator + fileName).length();  
    90.     }  
    91.       
    92.       
    93.     /** 
    94.      * 删除SD卡或者手机的缓存图片和目录 
    95.      */  
    96.     public void deleteFile() {  
    97.         File dirFile = new File(getStorageDirectory());  
    98.         if(! dirFile.exists()){  
    99.             return;  
    100.         }  
    101.         if (dirFile.isDirectory()) {  
    102.             String[] children = dirFile.list();  
    103.             for (int i = 0; i < children.length; i++) {  
    104.                 new File(dirFile, children[i]).delete();  
    105.             }  
    106.         }  
    107.           
    108.         dirFile.delete();  
    109.     }  
    110. }<span style="font-family:Times New Roman;font-size:14px;">  
    111. </span>  
    [java] view plaincopy
     
    1. package com.example.asyncimageloader;  
    2.   
    3. public class Images {  
    4.   
    5.     public final static String[] imageThumbUrls = new String[] {  
    6.             "https://lh6.googleusercontent.com/-55osAWw3x0Q/URquUtcFr5I/AAAAAAAAAbs/rWlj1RUKrYI/s160-c/A%252520Photographer.jpg",  
    7.             "https://lh4.googleusercontent.com/--dq8niRp7W4/URquVgmXvgI/AAAAAAAAAbs/-gnuLQfNnBA/s160-c/A%252520Song%252520of%252520Ice%252520and%252520Fire.jpg",  
    8.             "https://lh5.googleusercontent.com/-7qZeDtRKFKc/URquWZT1gOI/AAAAAAAAAbs/hqWgteyNXsg/s160-c/Another%252520Rockaway%252520Sunset.jpg",  
    9.             "https://lh3.googleusercontent.com/--L0Km39l5J8/URquXHGcdNI/AAAAAAAAAbs/3ZrSJNrSomQ/s160-c/Antelope%252520Butte.jpg",  
    10.             "https://lh6.googleusercontent.com/-8HO-4vIFnlw/URquZnsFgtI/AAAAAAAAAbs/WT8jViTF7vw/s160-c/Antelope%252520Hallway.jpg",  
    11.             "https://lh4.googleusercontent.com/-WIuWgVcU3Qw/URqubRVcj4I/AAAAAAAAAbs/YvbwgGjwdIQ/s160-c/Antelope%252520Walls.jpg",  
    12.             "https://lh6.googleusercontent.com/-UBmLbPELvoQ/URqucCdv0kI/AAAAAAAAAbs/IdNhr2VQoQs/s160-c/Apre%2525CC%252580s%252520la%252520Pluie.jpg",  
    13.             "https://lh3.googleusercontent.com/-s-AFpvgSeew/URquc6dF-JI/AAAAAAAAAbs/Mt3xNGRUd68/s160-c/Backlit%252520Cloud.jpg",  
    14.             "https://lh5.googleusercontent.com/-bvmif9a9YOQ/URquea3heHI/AAAAAAAAAbs/rcr6wyeQtAo/s160-c/Bee%252520and%252520Flower.jpg",  
    15.             "https://lh5.googleusercontent.com/-n7mdm7I7FGs/URqueT_BT-I/AAAAAAAAAbs/9MYmXlmpSAo/s160-c/Bonzai%252520Rock%252520Sunset.jpg",  
    16.             "https://lh6.googleusercontent.com/-4CN4X4t0M1k/URqufPozWzI/AAAAAAAAAbs/8wK41lg1KPs/s160-c/Caterpillar.jpg",  
    17.             "https://lh3.googleusercontent.com/-rrFnVC8xQEg/URqufdrLBaI/AAAAAAAAAbs/s69WYy_fl1E/s160-c/Chess.jpg",  
    18.             "https://lh5.googleusercontent.com/-WVpRptWH8Yw/URqugh-QmDI/AAAAAAAAAbs/E-MgBgtlUWU/s160-c/Chihuly.jpg",  
    19.             "https://lh5.googleusercontent.com/-0BDXkYmckbo/URquhKFW84I/AAAAAAAAAbs/ogQtHCTk2JQ/s160-c/Closed%252520Door.jpg",  
    20.             "https://lh3.googleusercontent.com/-PyggXXZRykM/URquh-kVvoI/AAAAAAAAAbs/hFtDwhtrHHQ/s160-c/Colorado%252520River%252520Sunset.jpg",  
    21.             "https://lh3.googleusercontent.com/-ZAs4dNZtALc/URquikvOCWI/AAAAAAAAAbs/DXz4h3dll1Y/s160-c/Colors%252520of%252520Autumn.jpg",  
    22.             "https://lh4.googleusercontent.com/-GztnWEIiMz8/URqukVCU7bI/AAAAAAAAAbs/jo2Hjv6MZ6M/s160-c/Countryside.jpg",  
    23.             "https://lh4.googleusercontent.com/-bEg9EZ9QoiM/URquklz3FGI/AAAAAAAAAbs/UUuv8Ac2BaE/s160-c/Death%252520Valley%252520-%252520Dunes.jpg",  
    24.             "https://lh6.googleusercontent.com/-ijQJ8W68tEE/URqulGkvFEI/AAAAAAAAAbs/zPXvIwi_rFw/s160-c/Delicate%252520Arch.jpg",  
    25.             "https://lh5.googleusercontent.com/-Oh8mMy2ieng/URqullDwehI/AAAAAAAAAbs/TbdeEfsaIZY/s160-c/Despair.jpg",  
    26.             "https://lh5.googleusercontent.com/-gl0y4UiAOlk/URqumC_KjBI/AAAAAAAAAbs/PM1eT7dn4oo/s160-c/Eagle%252520Fall%252520Sunrise.jpg",  
    27.             "https://lh3.googleusercontent.com/-hYYHd2_vXPQ/URqumtJa9eI/AAAAAAAAAbs/wAalXVkbSh0/s160-c/Electric%252520Storm.jpg",  
    28.             "https://lh5.googleusercontent.com/-PyY_yiyjPTo/URqunUOhHFI/AAAAAAAAAbs/azZoULNuJXc/s160-c/False%252520Kiva.jpg",  
    29.             "https://lh6.googleusercontent.com/-PYvLVdvXywk/URqunwd8hfI/AAAAAAAAAbs/qiMwgkFvf6I/s160-c/Fitzgerald%252520Streaks.jpg",  
    30.             "https://lh4.googleusercontent.com/-KIR_UobIIqY/URquoCZ9SlI/AAAAAAAAAbs/Y4d4q8sXu4c/s160-c/Foggy%252520Sunset.jpg",  
    31.             "https://lh6.googleusercontent.com/-9lzOk_OWZH0/URquoo4xYoI/AAAAAAAAAbs/AwgzHtNVCwU/s160-c/Frantic.jpg",  
    32.             "https://lh3.googleusercontent.com/-0X3JNaKaz48/URqupH78wpI/AAAAAAAAAbs/lHXxu_zbH8s/s160-c/Golden%252520Gate%252520Afternoon.jpg",  
    33.             "https://lh6.googleusercontent.com/-95sb5ag7ABc/URqupl95RDI/AAAAAAAAAbs/g73R20iVTRA/s160-c/Golden%252520Gate%252520Fog.jpg",  
    34.             "https://lh3.googleusercontent.com/-JB9v6rtgHhk/URqup21F-zI/AAAAAAAAAbs/64Fb8qMZWXk/s160-c/Golden%252520Grass.jpg",  
    35.             "https://lh4.googleusercontent.com/-EIBGfnuLtII/URquqVHwaRI/AAAAAAAAAbs/FA4McV2u8VE/s160-c/Grand%252520Teton.jpg",  
    36.             "https://lh4.googleusercontent.com/-WoMxZvmN9nY/URquq1v2AoI/AAAAAAAAAbs/grj5uMhL6NA/s160-c/Grass%252520Closeup.jpg",  
    37.             "https://lh3.googleusercontent.com/-6hZiEHXx64Q/URqurxvNdqI/AAAAAAAAAbs/kWMXM3o5OVI/s160-c/Green%252520Grass.jpg",  
    38.             "https://lh5.googleusercontent.com/-6LVb9OXtQ60/URquteBFuKI/AAAAAAAAAbs/4F4kRgecwFs/s160-c/Hanging%252520Leaf.jpg",  
    39.             "https://lh4.googleusercontent.com/-zAvf__52ONk/URqutT_IuxI/AAAAAAAAAbs/D_bcuc0thoU/s160-c/Highway%2525201.jpg",  
    40.             "https://lh6.googleusercontent.com/-H4SrUg615rA/URquuL27fXI/AAAAAAAAAbs/4aEqJfiMsOU/s160-c/Horseshoe%252520Bend%252520Sunset.jpg",  
    41.             "https://lh4.googleusercontent.com/-JhFi4fb_Pqw/URquuX-QXbI/AAAAAAAAAbs/IXpYUxuweYM/s160-c/Horseshoe%252520Bend.jpg",  
    42.             "https://lh5.googleusercontent.com/-UGgssvFRJ7g/URquueyJzGI/AAAAAAAAAbs/yYIBlLT0toM/s160-c/Into%252520the%252520Blue.jpg",  
    43.             "https://lh3.googleusercontent.com/-CH7KoupI7uI/URquu0FF__I/AAAAAAAAAbs/R7GDmI7v_G0/s160-c/Jelly%252520Fish%2525202.jpg",  
    44.             "https://lh4.googleusercontent.com/-pwuuw6yhg8U/URquvPxR3FI/AAAAAAAAAbs/VNGk6f-tsGE/s160-c/Jelly%252520Fish%2525203.jpg",  
    45.             "https://lh5.googleusercontent.com/-GoUQVw1fnFw/URquv6xbC0I/AAAAAAAAAbs/zEUVTQQ43Zc/s160-c/Kauai.jpg",  
    46.             "https://lh6.googleusercontent.com/-8QdYYQEpYjw/URquwvdh88I/AAAAAAAAAbs/cktDy-ysfHo/s160-c/Kyoto%252520Sunset.jpg",  
    47.             "https://lh4.googleusercontent.com/-vPeekyDjOE0/URquwzJ28qI/AAAAAAAAAbs/qxcyXULsZrg/s160-c/Lake%252520Tahoe%252520Colors.jpg",  
    48.             "https://lh4.googleusercontent.com/-xBPxWpD4yxU/URquxWHk8AI/AAAAAAAAAbs/ARDPeDYPiMY/s160-c/Lava%252520from%252520the%252520Sky.jpg",  
    49.             "https://lh3.googleusercontent.com/-897VXrJB6RE/URquxxxd-5I/AAAAAAAAAbs/j-Cz4T4YvIw/s160-c/Leica%25252050mm%252520Summilux.jpg",  
    50.             "https://lh5.googleusercontent.com/-qSJ4D4iXzGo/URquyDWiJ1I/AAAAAAAAAbs/k2pBXeWehOA/s160-c/Leica%25252050mm%252520Summilux.jpg",  
    51.             "https://lh6.googleusercontent.com/-dwlPg83vzLg/URquylTVuFI/AAAAAAAAAbs/G6SyQ8b4YsI/s160-c/Leica%252520M8%252520%252528Front%252529.jpg",  
    52.             "https://lh3.googleusercontent.com/-R3_EYAyJvfk/URquzQBv8eI/AAAAAAAAAbs/b9xhpUM3pEI/s160-c/Light%252520to%252520Sand.jpg",  
    53.             "https://lh3.googleusercontent.com/-fHY5h67QPi0/URqu0Cp4J1I/AAAAAAAAAbs/0lG6m94Z6vM/s160-c/Little%252520Bit%252520of%252520Paradise.jpg",  
    54.             "https://lh5.googleusercontent.com/-TzF_LwrCnRM/URqu0RddPOI/AAAAAAAAAbs/gaj2dLiuX0s/s160-c/Lone%252520Pine%252520Sunset.jpg",  
    55.             "https://lh3.googleusercontent.com/-4HdpJ4_DXU4/URqu046dJ9I/AAAAAAAAAbs/eBOodtk2_uk/s160-c/Lonely%252520Rock.jpg",  
    56.             "https://lh6.googleusercontent.com/-erbF--z-W4s/URqu1ajSLkI/AAAAAAAAAbs/xjDCDO1INzM/s160-c/Longue%252520Vue.jpg",  
    57.             "https://lh6.googleusercontent.com/-0CXJRdJaqvc/URqu1opNZNI/AAAAAAAAAbs/PFB2oPUU7Lk/s160-c/Look%252520Me%252520in%252520the%252520Eye.jpg",  
    58.             "https://lh3.googleusercontent.com/-D_5lNxnDN6g/URqu2Tk7HVI/AAAAAAAAAbs/p0ddca9W__Y/s160-c/Lost%252520in%252520a%252520Field.jpg",  
    59.             "https://lh6.googleusercontent.com/-flsqwMrIk2Q/URqu24PcmjI/AAAAAAAAAbs/5ocIH85XofM/s160-c/Marshall%252520Beach%252520Sunset.jpg",  
    60.             "https://lh4.googleusercontent.com/-Y4lgryEVTmU/URqu28kG3gI/AAAAAAAAAbs/OjXpekqtbJ4/s160-c/Mono%252520Lake%252520Blue.jpg",  
    61.             "https://lh4.googleusercontent.com/-AaHAJPmcGYA/URqu3PIldHI/AAAAAAAAAbs/lcTqk1SIcRs/s160-c/Monument%252520Valley%252520Overlook.jpg",  
    62.             "https://lh4.googleusercontent.com/-vKxfdQ83dQA/URqu31Yq_BI/AAAAAAAAAbs/OUoGk_2AyfM/s160-c/Moving%252520Rock.jpg",  
    63.             "https://lh5.googleusercontent.com/-CG62QiPpWXg/URqu4ia4vRI/AAAAAAAAAbs/0YOdqLAlcAc/s160-c/Napali%252520Coast.jpg",  
    64.             "https://lh6.googleusercontent.com/-wdGrP5PMmJQ/URqu5PZvn7I/AAAAAAAAAbs/m0abEcdPXe4/s160-c/One%252520Wheel.jpg",  
    65.             "https://lh6.googleusercontent.com/-6WS5DoCGuOA/URqu5qx1UgI/AAAAAAAAAbs/giMw2ixPvrY/s160-c/Open%252520Sky.jpg",  
    66.             "https://lh6.googleusercontent.com/-u8EHKj8G8GQ/URqu55sM6yI/AAAAAAAAAbs/lIXX_GlTdmI/s160-c/Orange%252520Sunset.jpg",  
    67.             "https://lh6.googleusercontent.com/-74Z5qj4bTDE/URqu6LSrJrI/AAAAAAAAAbs/XzmVkw90szQ/s160-c/Orchid.jpg",  
    68.             "https://lh6.googleusercontent.com/-lEQE4h6TePE/URqu6t_lSkI/AAAAAAAAAbs/zvGYKOea_qY/s160-c/Over%252520there.jpg",  
    69.             "https://lh5.googleusercontent.com/-cauH-53JH2M/URqu66v_USI/AAAAAAAAAbs/EucwwqclfKQ/s160-c/Plumes.jpg",  
    70.             "https://lh3.googleusercontent.com/-eDLT2jHDoy4/URqu7axzkAI/AAAAAAAAAbs/iVZE-xJ7lZs/s160-c/Rainbokeh.jpg",  
    71.             "https://lh5.googleusercontent.com/-j1NLqEFIyco/URqu8L1CGcI/AAAAAAAAAbs/aqZkgX66zlI/s160-c/Rainbow.jpg",  
    72.             "https://lh5.googleusercontent.com/-DRnqmK0t4VU/URqu8XYN9yI/AAAAAAAAAbs/LgvF_592WLU/s160-c/Rice%252520Fields.jpg",  
    73.             "https://lh3.googleusercontent.com/-hwh1v3EOGcQ/URqu8qOaKwI/AAAAAAAAAbs/IljRJRnbJGw/s160-c/Rockaway%252520Fire%252520Sky.jpg",  
    74.             "https://lh5.googleusercontent.com/-wjV6FQk7tlk/URqu9jCQ8sI/AAAAAAAAAbs/RyYUpdo-c9o/s160-c/Rockaway%252520Flow.jpg",  
    75.             "https://lh6.googleusercontent.com/-6cAXNfo7D20/URqu-BdzgPI/AAAAAAAAAbs/OmsYllzJqwo/s160-c/Rockaway%252520Sunset%252520Sky.jpg",  
    76.             "https://lh3.googleusercontent.com/-sl8fpGPS-RE/URqu_BOkfgI/AAAAAAAAAbs/Dg2Fv-JxOeg/s160-c/Russian%252520Ridge%252520Sunset.jpg",  
    77.             "https://lh6.googleusercontent.com/-gVtY36mMBIg/URqu_q91lkI/AAAAAAAAAbs/3CiFMBcy5MA/s160-c/Rust%252520Knot.jpg",  
    78.             "https://lh6.googleusercontent.com/-GHeImuHqJBE/URqu_FKfVLI/AAAAAAAAAbs/axuEJeqam7Q/s160-c/Sailing%252520Stones.jpg",  
    79.             "https://lh3.googleusercontent.com/-hBbYZjTOwGc/URqu_ycpIrI/AAAAAAAAAbs/nAdJUXnGJYE/s160-c/Seahorse.jpg",  
    80.             "https://lh3.googleusercontent.com/-Iwi6-i6IexY/URqvAYZHsVI/AAAAAAAAAbs/5ETWl4qXsFE/s160-c/Shinjuku%252520Street.jpg",  
    81.             "https://lh6.googleusercontent.com/-amhnySTM_MY/URqvAlb5KoI/AAAAAAAAAbs/pFCFgzlKsn0/s160-c/Sierra%252520Heavens.jpg",  
    82.             "https://lh5.googleusercontent.com/-dJgjepFrYSo/URqvBVJZrAI/AAAAAAAAAbs/v-F5QWpYO6s/s160-c/Sierra%252520Sunset.jpg",  
    83.             "https://lh4.googleusercontent.com/-Z4zGiC5nWdc/URqvBdEwivI/AAAAAAAAAbs/ZRZR1VJ84QA/s160-c/Sin%252520Lights.jpg",  
    84.             "https://lh4.googleusercontent.com/-_0cYiWW8ccY/URqvBz3iM4I/AAAAAAAAAbs/9N_Wq8MhLTY/s160-c/Starry%252520Lake.jpg",  
    85.             "https://lh3.googleusercontent.com/-A9LMoRyuQUA/URqvCYx_JoI/AAAAAAAAAbs/s7sde1Bz9cI/s160-c/Starry%252520Night.jpg",  
    86.             "https://lh3.googleusercontent.com/-KtLJ3k858eY/URqvC_2h_bI/AAAAAAAAAbs/zzEBImwDA_g/s160-c/Stream.jpg",  
    87.             "https://lh5.googleusercontent.com/-dFB7Lad6RcA/URqvDUftwWI/AAAAAAAAAbs/BrhoUtXTN7o/s160-c/Strip%252520Sunset.jpg",  
    88.             "https://lh5.googleusercontent.com/-at6apgFiN20/URqvDyffUZI/AAAAAAAAAbs/clABCx171bE/s160-c/Sunset%252520Hills.jpg",  
    89.             "https://lh4.googleusercontent.com/-7-EHhtQthII/URqvEYTk4vI/AAAAAAAAAbs/QSJZoB3YjVg/s160-c/Tenaya%252520Lake%2525202.jpg",  
    90.             "https://lh6.googleusercontent.com/-8MrjV_a-Pok/URqvFC5repI/AAAAAAAAAbs/9inKTg9fbCE/s160-c/Tenaya%252520Lake.jpg",  
    91.             "https://lh5.googleusercontent.com/-B1HW-z4zwao/URqvFWYRwUI/AAAAAAAAAbs/8Peli53Bs8I/s160-c/The%252520Cave%252520BW.jpg",  
    92.             "https://lh3.googleusercontent.com/-PO4E-xZKAnQ/URqvGRqjYkI/AAAAAAAAAbs/42nyADFsXag/s160-c/The%252520Fisherman.jpg",  
    93.             "https://lh4.googleusercontent.com/-iLyZlzfdy7s/URqvG0YScdI/AAAAAAAAAbs/1J9eDKmkXtk/s160-c/The%252520Night%252520is%252520Coming.jpg",  
    94.             "https://lh6.googleusercontent.com/-G-k7YkkUco0/URqvHhah6fI/AAAAAAAAAbs/_taQQG7t0vo/s160-c/The%252520Road.jpg",  
    95.             "https://lh6.googleusercontent.com/-h-ALJt7kSus/URqvIThqYfI/AAAAAAAAAbs/ejiv35olWS8/s160-c/Tokyo%252520Heights.jpg",  
    96.             "https://lh5.googleusercontent.com/-Hy9k-TbS7xg/URqvIjQMOxI/AAAAAAAAAbs/RSpmmOATSkg/s160-c/Tokyo%252520Highway.jpg",  
    97.             "https://lh6.googleusercontent.com/-83oOvMb4OZs/URqvJL0T7lI/AAAAAAAAAbs/c5TECZ6RONM/s160-c/Tokyo%252520Smog.jpg",  
    98.             "https://lh3.googleusercontent.com/-FB-jfgREEfI/URqvJI3EXAI/AAAAAAAAAbs/XfyweiRF4v8/s160-c/Tufa%252520at%252520Night.jpg",  
    99.             "https://lh4.googleusercontent.com/-vngKD5Z1U8w/URqvJUCEgPI/AAAAAAAAAbs/ulxCMVcU6EU/s160-c/Valley%252520Sunset.jpg",  
    100.             "https://lh6.googleusercontent.com/-DOz5I2E2oMQ/URqvKMND1kI/AAAAAAAAAbs/Iqf0IsInleo/s160-c/Windmill%252520Sunrise.jpg",  
    101.             "https://lh5.googleusercontent.com/-biyiyWcJ9MU/URqvKculiAI/AAAAAAAAAbs/jyPsCplJOpE/s160-c/Windmill.jpg",  
    102.             "https://lh4.googleusercontent.com/-PDT167_xRdA/URqvK36mLcI/AAAAAAAAAbs/oi2ik9QseMI/s160-c/Windmills.jpg",  
    103.             "https://lh5.googleusercontent.com/-kI_QdYx7VlU/URqvLXCB6gI/AAAAAAAAAbs/N31vlZ6u89o/s160-c/Yet%252520Another%252520Rockaway%252520Sunset.jpg",  
    104.             "https://lh4.googleusercontent.com/-e9NHZ5k5MSs/URqvMIBZjtI/AAAAAAAAAbs/1fV810rDNfQ/s160-c/Yosemite%252520Tree.jpg", };  
    105.       
    106. }<span style="font-family:Times New Roman;font-size:14px;">  
    107. </span>  
    • ImageDownLoader类，异步下载的核心类，保存图片到手机缓存，将图片加入LruCache中等等
    [java] view plaincopy
     
    1. package com.example.asyncimageloader;  
    2.   
    3. import java.io.IOException;  
    4. import java.net.HttpURLConnection;  
    5. import java.net.URL;  
    6. import java.util.concurrent.ExecutorService;  
    7. import java.util.concurrent.Executors;  
    8.   
    9. import android.content.Context;  
    10. import android.graphics.Bitmap;  
    11. import android.graphics.BitmapFactory;  
    12. import android.os.Handler;  
    13. import android.os.Message;  
    14. import android.support.v4.util.LruCache;  
    15.   
    16. public class ImageDownLoader {  
    17.     /** 
    18.      * 缓存Image的类，当存储Image的大小大于LruCache设定的值，系统自动释放内存 
    19.      */  
    20.     private LruCache<String, Bitmap> mMemoryCache;  
    21.     /** 
    22.      * 操作文件相关类对象的引用 
    23.      */  
    24.     private FileUtils fileUtils;  
    25.     /** 
    26.      * 下载Image的线程池 
    27.      */  
    28.     private ExecutorService mImageThreadPool = null;  
    29.       
    30.       
    31.     public ImageDownLoader(Context context){  
    32.         //获取系统分配给每个应用程序的最大内存，每个应用系统分配32M  
    33.         int maxMemory = (int) Runtime.getRuntime().maxMemory();    
    34.         int mCacheSize = maxMemory / 8;  
    35.         //给LruCache分配1/8 4M  
    36.         mMemoryCache = new LruCache<String, Bitmap>(mCacheSize){  
    37.   
    38.             //必须重写此方法，来测量Bitmap的大小  
    39.             @Override  
    40.             protected int sizeOf(String key, Bitmap value) {  
    41.                 return value.getRowBytes() * value.getHeight();  
    42.             }  
    43.               
    44.         };  
    45.           
    46.         fileUtils = new FileUtils(context);  
    47.     }  
    48.       
    49.       
    50.     /** 
    51.      * 获取线程池的方法，因为涉及到并发的问题，我们加上同步锁 
    52.      * @return 
    53.      */  
    54.     public ExecutorService getThreadPool(){  
    55.         if(mImageThreadPool == null){  
    56.             synchronized(ExecutorService.class){  
    57.                 if(mImageThreadPool == null){  
    58.                     //为了下载图片更加的流畅，我们用了2个线程来下载图片  
    59.                     mImageThreadPool = Executors.newFixedThreadPool(2);  
    60.                 }  
    61.             }  
    62.         }  
    63.           
    64.         return mImageThreadPool;  
    65.           
    66.     }  
    67.       
    68.     /** 
    69.      * 添加Bitmap到内存缓存 
    70.      * @param key 
    71.      * @param bitmap 
    72.      */  
    73.     public void addBitmapToMemoryCache(String key, Bitmap bitmap) {    
    74.         if (getBitmapFromMemCache(key) == null && bitmap != null) {    
    75.             mMemoryCache.put(key, bitmap);    
    76.         }    
    77.     }    
    78.        
    79.     /** 
    80.      * 从内存缓存中获取一个Bitmap 
    81.      * @param key 
    82.      * @return 
    83.      */  
    84.     public Bitmap getBitmapFromMemCache(String key) {    
    85.         return mMemoryCache.get(key);    
    86.     }   
    87.       
    88.     /** 
    89.      * 先从内存缓存中获取Bitmap,如果没有就从SD卡或者手机缓存中获取，SD卡或者手机缓存 
    90.      * 没有就去下载 
    91.      * @param url 
    92.      * @param listener 
    93.      * @return 
    94.      */  
    95.     public Bitmap downloadImage(final String url, final onImageLoaderListener listener){  
    96.         //替换Url中非字母和非数字的字符，这里比较重要，因为我们用Url作为文件名，比如我们的Url  
    97.         //是Http://xiaanming/abc.jpg;用这个作为图片名称，系统会认为xiaanming为一个目录，  
    98.         //我们没有创建此目录保存文件就会保存  
    99.         final String subUrl = url.replaceAll("[^\w]", "");  
    100.         Bitmap bitmap = showCacheBitmap(subUrl);  
    101.         if(bitmap != null){  
    102.             return bitmap;  
    103.         }else{  
    104.               
    105.             final Handler handler = new Handler(){  
    106.                 @Override  
    107.                 public void handleMessage(Message msg) {  
    108.                     super.handleMessage(msg);  
    109.                     listener.onImageLoader((Bitmap)msg.obj, url);  
    110.                 }  
    111.             };  
    112.               
    113.             getThreadPool().execute(new Runnable() {  
    114.                   
    115.                 @Override  
    116.                 public void run() {  
    117.                     Bitmap bitmap = getBitmapFormUrl(url);  
    118.                     Message msg = handler.obtainMessage();  
    119.                     msg.obj = bitmap;  
    120.                     handler.sendMessage(msg);  
    121.                       
    122.                     try {  
    123.                         //保存在SD卡或者手机目录  
    124.                         fileUtils.savaBitmap(subUrl, bitmap);  
    125.                     } catch (IOException e) {  
    126.                         e.printStackTrace();  
    127.                     }  
    128.                       
    129.                     //将Bitmap 加入内存缓存  
    130.                     addBitmapToMemoryCache(subUrl, bitmap);  
    131.                 }  
    132.             });  
    133.         }  
    134.           
    135.         return null;  
    136.     }  
    137.       
    138.     /** 
    139.      * 获取Bitmap, 内存中没有就去手机或者sd卡中获取，这一步在getView中会调用，比较关键的一步 
    140.      * @param url 
    141.      * @return 
    142.      */  
    143.     public Bitmap showCacheBitmap(String url){  
    144.         if(getBitmapFromMemCache(url) != null){  
    145.             return getBitmapFromMemCache(url);  
    146.         }else if(fileUtils.isFileExists(url) && fileUtils.getFileSize(url) != 0){  
    147.             //从SD卡获取手机里面获取Bitmap  
    148.             Bitmap bitmap = fileUtils.getBitmap(url);  
    149.               
    150.             //将Bitmap 加入内存缓存  
    151.             addBitmapToMemoryCache(url, bitmap);  
    152.             return bitmap;  
    153.         }  
    154.           
    155.         return null;  
    156.     }  
    157.       
    158.       
    159.     /** 
    160.      * 从Url中获取Bitmap 
    161.      * @param url 
    162.      * @return 
    163.      */  
    164.     private Bitmap getBitmapFormUrl(String url) {  
    165.         Bitmap bitmap = null;  
    166.         HttpURLConnection con = null;  
    167.         try {  
    168.             URL mImageUrl = new URL(url);  
    169.             con = (HttpURLConnection) mImageUrl.openConnection();  
    170.             con.setConnectTimeout(10 * 1000);  
    171.             con.setReadTimeout(10 * 1000);  
    172.             con.setDoInput(true);  
    173.             con.setDoOutput(true);  
    174.             bitmap = BitmapFactory.decodeStream(con.getInputStream());  
    175.         } catch (Exception e) {  
    176.             e.printStackTrace();  
    177.         } finally {  
    178.             if (con != null) {  
    179.                 con.disconnect();  
    180.             }  
    181.         }  
    182.         return bitmap;  
    183.     }  
    184.       
    185.     /** 
    186.      * 取消正在下载的任务 
    187.      */  
    188.     public synchronized void cancelTask() {  
    189.         if(mImageThreadPool != null){  
    190.             mImageThreadPool.shutdownNow();  
    191.             mImageThreadPool = null;  
    192.         }  
    193.     }  
    194.       
    195.       
    196.     /** 
    197.      * 异步下载图片的回调接口 
    198.      * @author len 
    199.      * 
    200.      */  
    201.     public interface onImageLoaderListener{  
    202.         void onImageLoader(Bitmap bitmap, String url);  
    203.     }  
    204.       
    205. }  

    ImageDownLoader中有几个方法比较重要

    1. 首先我们需要重写sizeOf(String key, Bitmap value)来计算图片的大小，默认返回图片的数量
    2. downloadImage(final String url, final onImageLoaderListener listener)先去LruCache查看Image,没有再去手机缓存中查看，在没有则开启线程下载，这里我们提供了一个回调接口，回调方法中我们将Bitmap和图片Url作为参数，String subUrl = url.replaceAll("[^\w]", "") 我在代码中注释写的比较清楚
    3. showCacheBitmap(String url)方法，此方法在Adapter中的getView()当中调用，如果getView()中不调用此方法试试你就知道效果了

     

    • ImageAdapter  GridView的适配器类，主要是GridView滑动的时候取消下载任务，静止的时候去下载当前显示的item的图片，其他也没什么不同了
    [java] view plaincopy
     
    1. package com.example.asyncimageloader;  
    2.   
    3. import android.content.Context;  
    4. import android.graphics.Bitmap;  
    5. import android.view.View;  
    6. import android.view.ViewGroup;  
    7. import android.widget.AbsListView;  
    8. import android.widget.AbsListView.OnScrollListener;  
    9. import android.widget.BaseAdapter;  
    10. import android.widget.GridView;  
    11. import android.widget.ImageView;  
    12.   
    13. import com.example.asyncimageloader.ImageDownLoader.onImageLoaderListener;  
    14.   
    15. public class ImageAdapter extends BaseAdapter implements OnScrollListener{  
    16.     /** 
    17.      * 上下文对象的引用 
    18.      */  
    19.     private Context context;  
    20.       
    21.     /** 
    22.      * Image Url的数组 
    23.      */  
    24.     private String [] imageThumbUrls;  
    25.       
    26.     /** 
    27.      * GridView对象的应用 
    28.      */  
    29.     private GridView mGridView;  
    30.       
    31.     /** 
    32.      * Image 下载器 
    33.      */  
    34.     private ImageDownLoader mImageDownLoader;  
    35.       
    36.     /** 
    37.      * 记录是否刚打开程序，用于解决进入程序不滚动屏幕，不会下载图片的问题。 
    38.      * 参考http://blog.csdn.net/guolin_blog/article/details/9526203#comments 
    39.      */  
    40.     private boolean isFirstEnter = true;  
    41.       
    42.     /** 
    43.      * 一屏中第一个item的位置 
    44.      */  
    45.     private int mFirstVisibleItem;  
    46.       
    47.     /** 
    48.      * 一屏中所有item的个数 
    49.      */  
    50.     private int mVisibleItemCount;  
    51.       
    52.       
    53.     public ImageAdapter(Context context, GridView mGridView, String [] imageThumbUrls){  
    54.         this.context = context;  
    55.         this.mGridView = mGridView;  
    56.         this.imageThumbUrls = imageThumbUrls;  
    57.         mImageDownLoader = new ImageDownLoader(context);  
    58.         mGridView.setOnScrollListener(this);  
    59.     }  
    60.       
    61.     @Override  
    62.     public void onScrollStateChanged(AbsListView view, int scrollState) {  
    63.         //仅当GridView静止时才去下载图片，GridView滑动时取消所有正在下载的任务    
    64.         if(scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE){  
    65.             showImage(mFirstVisibleItem, mVisibleItemCount);  
    66.         }else{  
    67.             cancelTask();  
    68.         }  
    69.           
    70.     }  
    71.   
    72.   
    73.     /** 
    74.      * GridView滚动的时候调用的方法，刚开始显示GridView也会调用此方法 
    75.      */  
    76.     @Override  
    77.     public void onScroll(AbsListView view, int firstVisibleItem,  
    78.             int visibleItemCount, int totalItemCount) {  
    79.         mFirstVisibleItem = firstVisibleItem;  
    80.         mVisibleItemCount = visibleItemCount;  
    81.         // 因此在这里为首次进入程序开启下载任务。   
    82.         if(isFirstEnter && visibleItemCount > 0){  
    83.             showImage(mFirstVisibleItem, mVisibleItemCount);  
    84.             isFirstEnter = false;  
    85.         }  
    86.     }  
    87.       
    88.   
    89.     @Override  
    90.     public int getCount() {  
    91.         return imageThumbUrls.length;  
    92.     }  
    93.   
    94.     @Override  
    95.     public Object getItem(int position) {  
    96.         return imageThumbUrls[position];  
    97.     }  
    98.   
    99.     @Override  
    100.     public long getItemId(int position) {  
    101.         return position;  
    102.     }  
    103.   
    104.     @Override  
    105.     public View getView(int position, View convertView, ViewGroup parent) {  
    106.         ImageView mImageView;  
    107.         final String mImageUrl = imageThumbUrls[position];  
    108.         if(convertView == null){  
    109.             mImageView = new ImageView(context);  
    110.         }else{  
    111.             mImageView = (ImageView) convertView;  
    112.         }  
    113.           
    114.         mImageView.setLayoutParams(new GridView.LayoutParams(150, 150));  
    115.         mImageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);  
    116.           
    117.         //给ImageView设置Tag,这里已经是司空见惯了  
    118.         mImageView.setTag(mImageUrl);  
    119.           
    120.           
    121.         /*******************************去掉下面这几行试试是什么效果****************************/  
    122.         Bitmap bitmap = mImageDownLoader.showCacheBitmap(mImageUrl.replaceAll("[^\w]", ""));  
    123.         if(bitmap != null){  
    124.             mImageView.setImageBitmap(bitmap);  
    125.         }else{  
    126.             mImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.ic_empty));  
    127.         }  
    128.         /**********************************************************************************/  
    129.           
    130.           
    131.         return mImageView;  
    132.     }  
    133.       
    134.     /** 
    135.      * 显示当前屏幕的图片，先会去查找LruCache，LruCache没有就去sd卡或者手机目录查找，在没有就开启线程去下载 
    136.      * @param firstVisibleItem 
    137.      * @param visibleItemCount 
    138.      */  
    139.     private void showImage(int firstVisibleItem, int visibleItemCount){  
    140.         Bitmap bitmap = null;  
    141.         for(int i=firstVisibleItem; i<firstVisibleItem + visibleItemCount; i++){  
    142.             String mImageUrl = imageThumbUrls[i];  
    143.             final ImageView mImageView = (ImageView) mGridView.findViewWithTag(mImageUrl);  
    144.             bitmap = mImageDownLoader.downloadImage(mImageUrl, new onImageLoaderListener() {  
    145.                   
    146.                 @Override  
    147.                 public void onImageLoader(Bitmap bitmap, String url) {  
    148.                     if(mImageView != null && bitmap != null){  
    149.                         mImageView.setImageBitmap(bitmap);  
    150.                     }  
    151.                       
    152.                 }  
    153.             });  
    154.               
    155.             if(bitmap != null){  
    156.                 mImageView.setImageBitmap(bitmap);  
    157.             }else{  
    158.                 mImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.ic_empty));  
    159.             }  
    160.         }  
    161.     }  
    162.   
    163.     /** 
    164.      * 取消下载任务 
    165.      */  
    166.     public void cancelTask(){  
    167.         mImageDownLoader.cancelTask();  
    168.     }  
    169.   
    170.   
    171. }  
    • MainActivity  里面一个GridView，然后提供一个系统菜单来删除手机上的缓存图片，直接上代码，比较简单所以里面也没有注释
    [java] view plaincopy
     
    1. package com.example.asyncimageloader;  
    2.   
    3. import android.app.Activity;  
    4. import android.os.Bundle;  
    5. import android.view.Menu;  
    6. import android.view.MenuItem;  
    7. import android.widget.GridView;  
    8. import android.widget.Toast;  
    9.   
    10. public class MainActivity extends Activity {  
    11.     private GridView mGridView;  
    12.     private String [] imageThumbUrls = Images.imageThumbUrls;   
    13.     private ImageAdapter mImageAdapter;  
    14.     private FileUtils fileUtils;  
    15.   
    16.     @Override  
    17.     protected void onCreate(Bundle savedInstanceState) {  
    18.         super.onCreate(savedInstanceState);  
    19.         setContentView(R.layout.activity_main);  
    20.         fileUtils = new FileUtils(this);  
    21.         mGridView = (GridView) findViewById(R.id.gridView);  
    22.         mImageAdapter = new ImageAdapter(this, mGridView, imageThumbUrls);  
    23.         mGridView.setAdapter(mImageAdapter);  
    24.     }  
    25.   
    26.     @Override  
    27.     protected void onDestroy() {  
    28.         mImageAdapter.cancelTask();  
    29.         super.onDestroy();  
    30.     }  
    31.   
    32.     @Override  
    33.     public boolean onCreateOptionsMenu(Menu menu) {  
    34.         super.onCreateOptionsMenu(menu);  
    35.         menu.add("删除手机中图片缓存");  
    36.         return super.onCreateOptionsMenu(menu);  
    37.     }  
    38.   
    39.     @Override  
    40.     public boolean onOptionsItemSelected(MenuItem item) {  
    41.         switch (item.getItemId()) {  
    42.         case 0:  
    43.             fileUtils.deleteFile();  
    44.             Toast.makeText(getApplication(), "清空缓存成功", Toast.LENGTH_SHORT).show();  
    45.             break;  
    46.         }  
    47.         return super.onOptionsItemSelected(item);  
    48.     }  
    49.   
    50. }<span style="font-family:Times New Roman;font-size:14px;">  
    51. </span>  
    • MainActivity的布局文件
    [html] view plaincopy
     
    1. <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    2.     xmlns:tools="http://schemas.android.com/tools"  
    3.     android:layout_width="match_parent"  
    4.     android:layout_height="match_parent"  
    5.     tools:context=".MainActivity" >  
    6.   
    7.     <GridView  
    8.         android:id="@+id/gridView"  
    9.         android:layout_width="match_parent"  
    10.         android:layout_height="match_parent"  
    11.         android:stretchMode="columnWidth"   
    12.         android:columnWidth="90dip"   
    13.         android:verticalSpacing="10dip"  
    14.         android:horizontalSpacing="10dip"  
    15.         android:cacheColorHint="@android:color/transparent"  
    16.         android:numColumns="auto_fit" >  
    17.     </GridView>  
    18.   
    19. </RelativeLayout>  
    • 因为有网络操作和对sd卡的操作，所以我们必须加上相对应的权限
    [html] view plaincopy
     
    1. <uses-permission android:name="android.permission.INTERNET" />   
    2. <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />   

    好了，代码就全部介绍完了，我们运行下程序看看效果，这里的效果是用一个线程下载图片的效果，可能有一些不完整，想看看效果自己动手试试，郁闷，家里的网络卡，gif的图片出不来效果，只能明天上传图片啦,公司也上传不了动画效果，我去，那我就贴一张普通图片，哈哈



    好了，今天的讲解到此结束，有疑问的朋友请在下面留言,源码里面GridView的布局文件 columnWedth设置了120dip,有点丑，大家可以改成90dip
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  • 原文地址：https://www.cnblogs.com/androidwsjisji/p/3247961.html
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