Android 异步加载图片，使用LruCache和SD卡或手机缓存，效果非常的流畅详解手机开发

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

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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.   

• Images类，提供图片资源的类，来自Android文档中BitmapFun中http://developer.android.com/training/displaying-bitmaps/index.html，里面一个静态的图片Url数组，这里面比较坑爹，因为是图片是google官网提供的，有时候会下载超时

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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.   

• 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]
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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报错  
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 plain
copy

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

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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.   

• MainActivity的布局文件

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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

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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

源码下载，点击这里