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
- 使用了线程池来管理下载任务
- 使用LruCache来缓存图片
- 使用手机来缓存图片
- 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
- 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
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. new File(path);
54. if(!folderFile.exists()){
55. folderFile.mkdir();
56. }
57. new File(path + File.separator + fileName);
58. file.createNewFile();
59. new FileOutputStream(file);
60. 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. 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>
- 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
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
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. 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. 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. 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. 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. null;
166. null;
167. try {
168. new URL(url);
169. con = (HttpURLConnection) mImageUrl.openConnection();
170. 10 * 1000);
171. 10 * 1000);
172. true);
173. 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. 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
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javascript:void(0)
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. new ImageDownLoader(context);
58. 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. 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. new ImageView(context);
110. else{
111. mImageView = (ImageView) convertView;
112. }
113.
114. 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. "[^\\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. null;
141. for(int i=firstVisibleItem; i<firstVisibleItem + visibleItemCount; i++){
142. String mImageUrl = imageThumbUrls[i];
143. final ImageView mImageView = (ImageView) mGridView.findViewWithTag(mImageUrl);
144. 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
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. new FileUtils(this);
21. mGridView = (GridView) findViewById(R.id.gridView);
22. 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. "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. "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
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
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