轉載請注明出處 http://blog.csdn.net/xiaanming/article/details/9825113
異步加載圖片的例子，網上也比較多，大部分用了HashMap<String, SoftReference<Drawable>> imageCache ，但是現在已經不再推薦使用這種方式了，因為從 Android 2.3 (API Level 9)開始，垃圾回收器會更傾向于回收持有軟引用或弱引用的對象，這讓軟引用和弱引用變得不再可靠。另外，Android 3.0 (API Level 11)中，圖片的數據會存儲在本地的內存當中，因而無法用一種可預見的方式將其釋放，這就有潛在的風險造成應用程序的內存溢出并崩潰，所以我這里用得是LruCache來緩存圖片，當存儲Image的大小大于LruCache設定的值，系統自動釋放內存，這個類是3.1版本中提供的，如果你是在更早的Android版本中開發，則需要導入android-support-v4的jar包（這里要注意咯）
為什么寫這篇文章呢？
因為我之前做的項目中，也有異步加載圖片，那時候用得是Thread去下載圖片，每次下載圖片都要new Thread去下載，而且還是并發去下載，每次都new 一個線程浪費內存，老板說服務器承受不起這么多的連接，叫我改成先獲取一張圖片之后再去獲取下一張，這樣子保存與服務器的連接為一個，服務器壓力小了，然后樓主就想到線程池，線程池很好的幫我們管理并發的問題，并發的問題解決了，可是后面又出問題了，圖片多了就出現OOM(OutOfMemory)異常，之后用了SoftReference，先用SoftReference中獲取圖片，SoftReference沒有就開線程去下載，老板說你為什么不把圖片在手機上做個緩存呢，于是我用了手機緩存，大概思路就是先從SoftReference中獲取圖片，如果SoftReference沒有就去手機緩存中獲取，手機緩存中沒有就開啟先從去下載，然后成功的解決了OOM的問題，前些天老板要我重構下代碼，我也覺得之前寫的代碼耦合性太強，早就想改，然后之前看到guolin的 Android照片墻應用實現，再多的圖片也不怕崩潰 的這篇文章，LruCache和滑動過程中取消下載任務，停下來的時候才去下載這2點比較好，值得我學習，然后我就將我的項目異步加載這一塊改了下，發到這里做個記錄吧，以后類似的異步加載圖片直接拷貝代碼，提交開發的效率
這篇文章做了哪些方面的優化
- 使用了線程池來管理下載任務
- 使用LruCache來緩存圖片
- 使用手機來緩存圖片
- GridView滑動的時候取消下載任務，靜止的時候進行下載，GridView滑動更加的流暢
- 降低了代碼的耦合性，結構更加的清晰，便于以后重用
接下來我們先來看看項目的結構
- FileUtils 文件操作的工具類，提供保存圖片，獲取圖片，判斷圖片是否存在，刪除圖片的一些方法，這個類比較簡單
package com.example.asyncimageloader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.os.Environment;
public class FileUtils {
/**
* sd卡的根目錄
*/
private static String mSdRootPath = Environment.getExternalStorageDirectory().getPath();
/**
* 手機的緩存根目錄
*/
private static String mDataRootPath = null;
/**
* 保存Image的目錄名
*/
private final static String FOLDER_NAME = "/AndroidImage";
public FileUtils(Context context){
mDataRootPath = context.getCacheDir().getPath();
}
/**
* 獲取儲存Image的目錄
* @return
*/
private String getStorageDirectory(){
return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ?
mSdRootPath + FOLDER_NAME : mDataRootPath + FOLDER_NAME;
}
/**
* 保存Image的方法，有sd卡存儲到sd卡，沒有就存儲到手機目錄
* @param fileName
* @param bitmap
* @throws IOException
*/
public void savaBitmap(String fileName, Bitmap bitmap) throws IOException{
if(bitmap == null){
return;
}
String path = getStorageDirectory();
File folderFile = new File(path);
if(!folderFile.exists()){
folderFile.mkdir();
}
File file = new File(path + File.separator + fileName);
file.createNewFile();
FileOutputStream fos = new FileOutputStream(file);
bitmap.compress(CompressFormat.JPEG, 100, fos);
fos.flush();
fos.close();
}
/**
* 從手機或者sd卡獲取Bitmap
* @param fileName
* @return
*/
public Bitmap getBitmap(String fileName){
return BitmapFactory.decodeFile(getStorageDirectory() + File.separator + fileName);
}
/**
* 判斷文件是否存在
* @param fileName
* @return
*/
public boolean isFileExists(String fileName){
return new File(getStorageDirectory() + File.separator + fileName).exists();
}
/**
* 獲取文件的大小
* @param fileName
* @return
*/
public long getFileSize(String fileName) {
return new File(getStorageDirectory() + File.separator + fileName).length();
}
/**
* 刪除SD卡或者手機的緩存圖片和目錄
*/
public void deleteFile() {
File dirFile = new File(getStorageDirectory());
if(! dirFile.exists()){
return;
}
if (dirFile.isDirectory()) {
String[] children = dirFile.list();
for (int i = 0; i < children.length; i++) {
new File(dirFile, children[i]).delete();
}
}
dirFile.delete();
}
}
- Images類，提供圖片資源的類，來自Android文檔中BitmapFun中 http://developer.android.com/training/displaying-bitmaps/index.html ，里面一個靜態的圖片Url數組，這里面比較坑爹，因為是圖片是google官網提供的，有時候會下載超時
package com.example.asyncimageloader;
public class Images {
public final static String[] imageThumbUrls = new String[] {
"https://lh6.googleusercontent.com/-55osAWw3x0Q/URquUtcFr5I/AAAAAAAAAbs/rWlj1RUKrYI/s160-c/A%252520Photographer.jpg",
"https://lh4.googleusercontent.com/--dq8niRp7W4/URquVgmXvgI/AAAAAAAAAbs/-gnuLQfNnBA/s160-c/A%252520Song%252520of%252520Ice%252520and%252520Fire.jpg",
"https://lh5.googleusercontent.com/-7qZeDtRKFKc/URquWZT1gOI/AAAAAAAAAbs/hqWgteyNXsg/s160-c/Another%252520Rockaway%252520Sunset.jpg",
"https://lh3.googleusercontent.com/--L0Km39l5J8/URquXHGcdNI/AAAAAAAAAbs/3ZrSJNrSomQ/s160-c/Antelope%252520Butte.jpg",
"https://lh6.googleusercontent.com/-8HO-4vIFnlw/URquZnsFgtI/AAAAAAAAAbs/WT8jViTF7vw/s160-c/Antelope%252520Hallway.jpg",
"https://lh4.googleusercontent.com/-WIuWgVcU3Qw/URqubRVcj4I/AAAAAAAAAbs/YvbwgGjwdIQ/s160-c/Antelope%252520Walls.jpg",
"https://lh6.googleusercontent.com/-UBmLbPELvoQ/URqucCdv0kI/AAAAAAAAAbs/IdNhr2VQoQs/s160-c/Apre%2525CC%252580s%252520la%252520Pluie.jpg",
"https://lh3.googleusercontent.com/-s-AFpvgSeew/URquc6dF-JI/AAAAAAAAAbs/Mt3xNGRUd68/s160-c/Backlit%252520Cloud.jpg",
"https://lh5.googleusercontent.com/-bvmif9a9YOQ/URquea3heHI/AAAAAAAAAbs/rcr6wyeQtAo/s160-c/Bee%252520and%252520Flower.jpg",
"https://lh5.googleusercontent.com/-n7mdm7I7FGs/URqueT_BT-I/AAAAAAAAAbs/9MYmXlmpSAo/s160-c/Bonzai%252520Rock%252520Sunset.jpg",
"https://lh6.googleusercontent.com/-4CN4X4t0M1k/URqufPozWzI/AAAAAAAAAbs/8wK41lg1KPs/s160-c/Caterpillar.jpg",
"https://lh3.googleusercontent.com/-rrFnVC8xQEg/URqufdrLBaI/AAAAAAAAAbs/s69WYy_fl1E/s160-c/Chess.jpg",
"https://lh5.googleusercontent.com/-WVpRptWH8Yw/URqugh-QmDI/AAAAAAAAAbs/E-MgBgtlUWU/s160-c/Chihuly.jpg",
"https://lh5.googleusercontent.com/-0BDXkYmckbo/URquhKFW84I/AAAAAAAAAbs/ogQtHCTk2JQ/s160-c/Closed%252520Door.jpg",
"https://lh3.googleusercontent.com/-PyggXXZRykM/URquh-kVvoI/AAAAAAAAAbs/hFtDwhtrHHQ/s160-c/Colorado%252520River%252520Sunset.jpg",
"https://lh3.googleusercontent.com/-ZAs4dNZtALc/URquikvOCWI/AAAAAAAAAbs/DXz4h3dll1Y/s160-c/Colors%252520of%252520Autumn.jpg",
"https://lh4.googleusercontent.com/-GztnWEIiMz8/URqukVCU7bI/AAAAAAAAAbs/jo2Hjv6MZ6M/s160-c/Countryside.jpg",
"https://lh4.googleusercontent.com/-bEg9EZ9QoiM/URquklz3FGI/AAAAAAAAAbs/UUuv8Ac2BaE/s160-c/Death%252520Valley%252520-%252520Dunes.jpg",
"https://lh6.googleusercontent.com/-ijQJ8W68tEE/URqulGkvFEI/AAAAAAAAAbs/zPXvIwi_rFw/s160-c/Delicate%252520Arch.jpg",
"https://lh5.googleusercontent.com/-Oh8mMy2ieng/URqullDwehI/AAAAAAAAAbs/TbdeEfsaIZY/s160-c/Despair.jpg",
"https://lh5.googleusercontent.com/-gl0y4UiAOlk/URqumC_KjBI/AAAAAAAAAbs/PM1eT7dn4oo/s160-c/Eagle%252520Fall%252520Sunrise.jpg",
"https://lh3.googleusercontent.com/-hYYHd2_vXPQ/URqumtJa9eI/AAAAAAAAAbs/wAalXVkbSh0/s160-c/Electric%252520Storm.jpg",
"https://lh5.googleusercontent.com/-PyY_yiyjPTo/URqunUOhHFI/AAAAAAAAAbs/azZoULNuJXc/s160-c/False%252520Kiva.jpg",
"https://lh6.googleusercontent.com/-PYvLVdvXywk/URqunwd8hfI/AAAAAAAAAbs/qiMwgkFvf6I/s160-c/Fitzgerald%252520Streaks.jpg",
"https://lh4.googleusercontent.com/-KIR_UobIIqY/URquoCZ9SlI/AAAAAAAAAbs/Y4d4q8sXu4c/s160-c/Foggy%252520Sunset.jpg",
"https://lh6.googleusercontent.com/-9lzOk_OWZH0/URquoo4xYoI/AAAAAAAAAbs/AwgzHtNVCwU/s160-c/Frantic.jpg",
"https://lh3.googleusercontent.com/-0X3JNaKaz48/URqupH78wpI/AAAAAAAAAbs/lHXxu_zbH8s/s160-c/Golden%252520Gate%252520Afternoon.jpg",
"https://lh6.googleusercontent.com/-95sb5ag7ABc/URqupl95RDI/AAAAAAAAAbs/g73R20iVTRA/s160-c/Golden%252520Gate%252520Fog.jpg",
"https://lh3.googleusercontent.com/-JB9v6rtgHhk/URqup21F-zI/AAAAAAAAAbs/64Fb8qMZWXk/s160-c/Golden%252520Grass.jpg",
"https://lh4.googleusercontent.com/-EIBGfnuLtII/URquqVHwaRI/AAAAAAAAAbs/FA4McV2u8VE/s160-c/Grand%252520Teton.jpg",
"https://lh4.googleusercontent.com/-WoMxZvmN9nY/URquq1v2AoI/AAAAAAAAAbs/grj5uMhL6NA/s160-c/Grass%252520Closeup.jpg",
"https://lh3.googleusercontent.com/-6hZiEHXx64Q/URqurxvNdqI/AAAAAAAAAbs/kWMXM3o5OVI/s160-c/Green%252520Grass.jpg",
"https://lh5.googleusercontent.com/-6LVb9OXtQ60/URquteBFuKI/AAAAAAAAAbs/4F4kRgecwFs/s160-c/Hanging%252520Leaf.jpg",
"https://lh4.googleusercontent.com/-zAvf__52ONk/URqutT_IuxI/AAAAAAAAAbs/D_bcuc0thoU/s160-c/Highway%2525201.jpg",
"https://lh6.googleusercontent.com/-H4SrUg615rA/URquuL27fXI/AAAAAAAAAbs/4aEqJfiMsOU/s160-c/Horseshoe%252520Bend%252520Sunset.jpg",
"https://lh4.googleusercontent.com/-JhFi4fb_Pqw/URquuX-QXbI/AAAAAAAAAbs/IXpYUxuweYM/s160-c/Horseshoe%252520Bend.jpg",
"https://lh5.googleusercontent.com/-UGgssvFRJ7g/URquueyJzGI/AAAAAAAAAbs/yYIBlLT0toM/s160-c/Into%252520the%252520Blue.jpg",
"https://lh3.googleusercontent.com/-CH7KoupI7uI/URquu0FF__I/AAAAAAAAAbs/R7GDmI7v_G0/s160-c/Jelly%252520Fish%2525202.jpg",
"https://lh4.googleusercontent.com/-pwuuw6yhg8U/URquvPxR3FI/AAAAAAAAAbs/VNGk6f-tsGE/s160-c/Jelly%252520Fish%2525203.jpg",
"https://lh5.googleusercontent.com/-GoUQVw1fnFw/URquv6xbC0I/AAAAAAAAAbs/zEUVTQQ43Zc/s160-c/Kauai.jpg",
"https://lh6.googleusercontent.com/-8QdYYQEpYjw/URquwvdh88I/AAAAAAAAAbs/cktDy-ysfHo/s160-c/Kyoto%252520Sunset.jpg",
"https://lh4.googleusercontent.com/-vPeekyDjOE0/URquwzJ28qI/AAAAAAAAAbs/qxcyXULsZrg/s160-c/Lake%252520Tahoe%252520Colors.jpg",
"https://lh4.googleusercontent.com/-xBPxWpD4yxU/URquxWHk8AI/AAAAAAAAAbs/ARDPeDYPiMY/s160-c/Lava%252520from%252520the%252520Sky.jpg",
"https://lh3.googleusercontent.com/-897VXrJB6RE/URquxxxd-5I/AAAAAAAAAbs/j-Cz4T4YvIw/s160-c/Leica%25252050mm%252520Summilux.jpg",
"https://lh5.googleusercontent.com/-qSJ4D4iXzGo/URquyDWiJ1I/AAAAAAAAAbs/k2pBXeWehOA/s160-c/Leica%25252050mm%252520Summilux.jpg",
"https://lh6.googleusercontent.com/-dwlPg83vzLg/URquylTVuFI/AAAAAAAAAbs/G6SyQ8b4YsI/s160-c/Leica%252520M8%252520%252528Front%252529.jpg",
"https://lh3.googleusercontent.com/-R3_EYAyJvfk/URquzQBv8eI/AAAAAAAAAbs/b9xhpUM3pEI/s160-c/Light%252520to%252520Sand.jpg",
"https://lh3.googleusercontent.com/-fHY5h67QPi0/URqu0Cp4J1I/AAAAAAAAAbs/0lG6m94Z6vM/s160-c/Little%252520Bit%252520of%252520Paradise.jpg",
"https://lh5.googleusercontent.com/-TzF_LwrCnRM/URqu0RddPOI/AAAAAAAAAbs/gaj2dLiuX0s/s160-c/Lone%252520Pine%252520Sunset.jpg",
"https://lh3.googleusercontent.com/-4HdpJ4_DXU4/URqu046dJ9I/AAAAAAAAAbs/eBOodtk2_uk/s160-c/Lonely%252520Rock.jpg",
"https://lh6.googleusercontent.com/-erbF--z-W4s/URqu1ajSLkI/AAAAAAAAAbs/xjDCDO1INzM/s160-c/Longue%252520Vue.jpg",
"https://lh6.googleusercontent.com/-0CXJRdJaqvc/URqu1opNZNI/AAAAAAAAAbs/PFB2oPUU7Lk/s160-c/Look%252520Me%252520in%252520the%252520Eye.jpg",
"https://lh3.googleusercontent.com/-D_5lNxnDN6g/URqu2Tk7HVI/AAAAAAAAAbs/p0ddca9W__Y/s160-c/Lost%252520in%252520a%252520Field.jpg",
"https://lh6.googleusercontent.com/-flsqwMrIk2Q/URqu24PcmjI/AAAAAAAAAbs/5ocIH85XofM/s160-c/Marshall%252520Beach%252520Sunset.jpg",
"https://lh4.googleusercontent.com/-Y4lgryEVTmU/URqu28kG3gI/AAAAAAAAAbs/OjXpekqtbJ4/s160-c/Mono%252520Lake%252520Blue.jpg",
"https://lh4.googleusercontent.com/-AaHAJPmcGYA/URqu3PIldHI/AAAAAAAAAbs/lcTqk1SIcRs/s160-c/Monument%252520Valley%252520Overlook.jpg",
"https://lh4.googleusercontent.com/-vKxfdQ83dQA/URqu31Yq_BI/AAAAAAAAAbs/OUoGk_2AyfM/s160-c/Moving%252520Rock.jpg",
"https://lh5.googleusercontent.com/-CG62QiPpWXg/URqu4ia4vRI/AAAAAAAAAbs/0YOdqLAlcAc/s160-c/Napali%252520Coast.jpg",
"https://lh6.googleusercontent.com/-wdGrP5PMmJQ/URqu5PZvn7I/AAAAAAAAAbs/m0abEcdPXe4/s160-c/One%252520Wheel.jpg",
"https://lh6.googleusercontent.com/-6WS5DoCGuOA/URqu5qx1UgI/AAAAAAAAAbs/giMw2ixPvrY/s160-c/Open%252520Sky.jpg",
"https://lh6.googleusercontent.com/-u8EHKj8G8GQ/URqu55sM6yI/AAAAAAAAAbs/lIXX_GlTdmI/s160-c/Orange%252520Sunset.jpg",
"https://lh6.googleusercontent.com/-74Z5qj4bTDE/URqu6LSrJrI/AAAAAAAAAbs/XzmVkw90szQ/s160-c/Orchid.jpg",
"https://lh6.googleusercontent.com/-lEQE4h6TePE/URqu6t_lSkI/AAAAAAAAAbs/zvGYKOea_qY/s160-c/Over%252520there.jpg",
"https://lh5.googleusercontent.com/-cauH-53JH2M/URqu66v_USI/AAAAAAAAAbs/EucwwqclfKQ/s160-c/Plumes.jpg",
"https://lh3.googleusercontent.com/-eDLT2jHDoy4/URqu7axzkAI/AAAAAAAAAbs/iVZE-xJ7lZs/s160-c/Rainbokeh.jpg",
"https://lh5.googleusercontent.com/-j1NLqEFIyco/URqu8L1CGcI/AAAAAAAAAbs/aqZkgX66zlI/s160-c/Rainbow.jpg",
"https://lh5.googleusercontent.com/-DRnqmK0t4VU/URqu8XYN9yI/AAAAAAAAAbs/LgvF_592WLU/s160-c/Rice%252520Fields.jpg",
"https://lh3.googleusercontent.com/-hwh1v3EOGcQ/URqu8qOaKwI/AAAAAAAAAbs/IljRJRnbJGw/s160-c/Rockaway%252520Fire%252520Sky.jpg",
"https://lh5.googleusercontent.com/-wjV6FQk7tlk/URqu9jCQ8sI/AAAAAAAAAbs/RyYUpdo-c9o/s160-c/Rockaway%252520Flow.jpg",
"https://lh6.googleusercontent.com/-6cAXNfo7D20/URqu-BdzgPI/AAAAAAAAAbs/OmsYllzJqwo/s160-c/Rockaway%252520Sunset%252520Sky.jpg",
"https://lh3.googleusercontent.com/-sl8fpGPS-RE/URqu_BOkfgI/AAAAAAAAAbs/Dg2Fv-JxOeg/s160-c/Russian%252520Ridge%252520Sunset.jpg",
"https://lh6.googleusercontent.com/-gVtY36mMBIg/URqu_q91lkI/AAAAAAAAAbs/3CiFMBcy5MA/s160-c/Rust%252520Knot.jpg",
"https://lh6.googleusercontent.com/-GHeImuHqJBE/URqu_FKfVLI/AAAAAAAAAbs/axuEJeqam7Q/s160-c/Sailing%252520Stones.jpg",
"https://lh3.googleusercontent.com/-hBbYZjTOwGc/URqu_ycpIrI/AAAAAAAAAbs/nAdJUXnGJYE/s160-c/Seahorse.jpg",
"https://lh3.googleusercontent.com/-Iwi6-i6IexY/URqvAYZHsVI/AAAAAAAAAbs/5ETWl4qXsFE/s160-c/Shinjuku%252520Street.jpg",
"https://lh6.googleusercontent.com/-amhnySTM_MY/URqvAlb5KoI/AAAAAAAAAbs/pFCFgzlKsn0/s160-c/Sierra%252520Heavens.jpg",
"https://lh5.googleusercontent.com/-dJgjepFrYSo/URqvBVJZrAI/AAAAAAAAAbs/v-F5QWpYO6s/s160-c/Sierra%252520Sunset.jpg",
"https://lh4.googleusercontent.com/-Z4zGiC5nWdc/URqvBdEwivI/AAAAAAAAAbs/ZRZR1VJ84QA/s160-c/Sin%252520Lights.jpg",
"https://lh4.googleusercontent.com/-_0cYiWW8ccY/URqvBz3iM4I/AAAAAAAAAbs/9N_Wq8MhLTY/s160-c/Starry%252520Lake.jpg",
"https://lh3.googleusercontent.com/-A9LMoRyuQUA/URqvCYx_JoI/AAAAAAAAAbs/s7sde1Bz9cI/s160-c/Starry%252520Night.jpg",
"https://lh3.googleusercontent.com/-KtLJ3k858eY/URqvC_2h_bI/AAAAAAAAAbs/zzEBImwDA_g/s160-c/Stream.jpg",
"https://lh5.googleusercontent.com/-dFB7Lad6RcA/URqvDUftwWI/AAAAAAAAAbs/BrhoUtXTN7o/s160-c/Strip%252520Sunset.jpg",
"https://lh5.googleusercontent.com/-at6apgFiN20/URqvDyffUZI/AAAAAAAAAbs/clABCx171bE/s160-c/Sunset%252520Hills.jpg",
"https://lh4.googleusercontent.com/-7-EHhtQthII/URqvEYTk4vI/AAAAAAAAAbs/QSJZoB3YjVg/s160-c/Tenaya%252520Lake%2525202.jpg",
"https://lh6.googleusercontent.com/-8MrjV_a-Pok/URqvFC5repI/AAAAAAAAAbs/9inKTg9fbCE/s160-c/Tenaya%252520Lake.jpg",
"https://lh5.googleusercontent.com/-B1HW-z4zwao/URqvFWYRwUI/AAAAAAAAAbs/8Peli53Bs8I/s160-c/The%252520Cave%252520BW.jpg",
"https://lh3.googleusercontent.com/-PO4E-xZKAnQ/URqvGRqjYkI/AAAAAAAAAbs/42nyADFsXag/s160-c/The%252520Fisherman.jpg",
"https://lh4.googleusercontent.com/-iLyZlzfdy7s/URqvG0YScdI/AAAAAAAAAbs/1J9eDKmkXtk/s160-c/The%252520Night%252520is%252520Coming.jpg",
"https://lh6.googleusercontent.com/-G-k7YkkUco0/URqvHhah6fI/AAAAAAAAAbs/_taQQG7t0vo/s160-c/The%252520Road.jpg",
"https://lh6.googleusercontent.com/-h-ALJt7kSus/URqvIThqYfI/AAAAAAAAAbs/ejiv35olWS8/s160-c/Tokyo%252520Heights.jpg",
"https://lh5.googleusercontent.com/-Hy9k-TbS7xg/URqvIjQMOxI/AAAAAAAAAbs/RSpmmOATSkg/s160-c/Tokyo%252520Highway.jpg",
"https://lh6.googleusercontent.com/-83oOvMb4OZs/URqvJL0T7lI/AAAAAAAAAbs/c5TECZ6RONM/s160-c/Tokyo%252520Smog.jpg",
"https://lh3.googleusercontent.com/-FB-jfgREEfI/URqvJI3EXAI/AAAAAAAAAbs/XfyweiRF4v8/s160-c/Tufa%252520at%252520Night.jpg",
"https://lh4.googleusercontent.com/-vngKD5Z1U8w/URqvJUCEgPI/AAAAAAAAAbs/ulxCMVcU6EU/s160-c/Valley%252520Sunset.jpg",
"https://lh6.googleusercontent.com/-DOz5I2E2oMQ/URqvKMND1kI/AAAAAAAAAbs/Iqf0IsInleo/s160-c/Windmill%252520Sunrise.jpg",
"https://lh5.googleusercontent.com/-biyiyWcJ9MU/URqvKculiAI/AAAAAAAAAbs/jyPsCplJOpE/s160-c/Windmill.jpg",
"https://lh4.googleusercontent.com/-PDT167_xRdA/URqvK36mLcI/AAAAAAAAAbs/oi2ik9QseMI/s160-c/Windmills.jpg",
"https://lh5.googleusercontent.com/-kI_QdYx7VlU/URqvLXCB6gI/AAAAAAAAAbs/N31vlZ6u89o/s160-c/Yet%252520Another%252520Rockaway%252520Sunset.jpg",
"https://lh4.googleusercontent.com/-e9NHZ5k5MSs/URqvMIBZjtI/AAAAAAAAAbs/1fV810rDNfQ/s160-c/Yosemite%252520Tree.jpg", };
}
- ImageDownLoader類，異步下載的核心類，保存圖片到手機緩存，將圖片加入LruCache中等等
package com.example.asyncimageloader;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;
public class ImageDownLoader {
/**
* 緩存Image的類，當存儲Image的大小大于LruCache設定的值，系統自動釋放內存
*/
private LruCache<String, Bitmap> mMemoryCache;
/**
* 操作文件相關類對象的引用
*/
private FileUtils fileUtils;
/**
* 下載Image的線程池
*/
private ExecutorService mImageThreadPool = null;
public ImageDownLoader(Context context){
//獲取系統分配給每個應用程序的最大內存，每個應用系統分配32M
int maxMemory = (int) Runtime.getRuntime().maxMemory();
int mCacheSize = maxMemory / 8;
//給LruCache分配1/8 4M
mMemoryCache = new LruCache<String, Bitmap>(mCacheSize){
//必須重寫此方法，來測量Bitmap的大小
@Override
protected int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
};
fileUtils = new FileUtils(context);
}
/**
* 獲取線程池的方法，因為涉及到并發的問題，我們加上同步鎖
* @return
*/
public ExecutorService getThreadPool(){
if(mImageThreadPool == null){
synchronized(ExecutorService.class){
if(mImageThreadPool == null){
//為了下載圖片更加的流暢，我們用了2個線程來下載圖片
mImageThreadPool = Executors.newFixedThreadPool(2);
}
}
}
return mImageThreadPool;
}
/**
* 添加Bitmap到內存緩存
* @param key
* @param bitmap
*/
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null && bitmap != null) {
mMemoryCache.put(key, bitmap);
}
}
/**
* 從內存緩存中獲取一個Bitmap
* @param key
* @return
*/
public Bitmap getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
/**
* 先從內存緩存中獲取Bitmap,如果沒有就從SD卡或者手機緩存中獲取，SD卡或者手機緩存
* 沒有就去下載
* @param url
* @param listener
* @return
*/
public Bitmap downloadImage(final String url, final onImageLoaderListener listener){
//替換Url中非字母和非數字的字符，這里比較重要，因為我們用Url作為文件名，比如我們的Url
//是Http://xiaanming/abc.jpg;用這個作為圖片名稱，系統會認為xiaanming為一個目錄，
//我們沒有創建此目錄保存文件就會報錯
final String subUrl = url.replaceAll("[^\\w]", "");
Bitmap bitmap = showCacheBitmap(subUrl);
if(bitmap != null){
return bitmap;
}else{
final Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
listener.onImageLoader((Bitmap)msg.obj, url);
}
};
getThreadPool().execute(new Runnable() {
@Override
public void run() {
Bitmap bitmap = getBitmapFormUrl(url);
Message msg = handler.obtainMessage();
msg.obj = bitmap;
handler.sendMessage(msg);
try {
//保存在SD卡或者手機目錄
fileUtils.savaBitmap(subUrl, bitmap);
} catch (IOException e) {
e.printStackTrace();
}
//將Bitmap 加入內存緩存
addBitmapToMemoryCache(subUrl, bitmap);
}
});
}
return null;
}
/**
* 獲取Bitmap, 內存中沒有就去手機或者sd卡中獲取，這一步在getView中會調用，比較關鍵的一步
* @param url
* @return
*/
public Bitmap showCacheBitmap(String url){
if(getBitmapFromMemCache(url) != null){
return getBitmapFromMemCache(url);
}else if(fileUtils.isFileExists(url) && fileUtils.getFileSize(url) != 0){
//從SD卡獲取手機里面獲取Bitmap
Bitmap bitmap = fileUtils.getBitmap(url);
//將Bitmap 加入內存緩存
addBitmapToMemoryCache(url, bitmap);
return bitmap;
}
return null;
}
/**
* 從Url中獲取Bitmap
* @param url
* @return
*/
private Bitmap getBitmapFormUrl(String url) {
Bitmap bitmap = null;
HttpURLConnection con = null;
try {
URL mImageUrl = new URL(url);
con = (HttpURLConnection) mImageUrl.openConnection();
con.setConnectTimeout(10 * 1000);
con.setReadTimeout(10 * 1000);
con.setDoInput(true);
con.setDoOutput(true);
bitmap = BitmapFactory.decodeStream(con.getInputStream());
} catch (Exception e) {
e.printStackTrace();
} finally {
if (con != null) {
con.disconnect();
}
}
return bitmap;
}
/**
* 取消正在下載的任務
*/
public synchronized void cancelTask() {
if(mImageThreadPool != null){
mImageThreadPool.shutdownNow();
mImageThreadPool = null;
}
}
/**
* 異步下載圖片的回調接口
* @author len
*
*/
public interface onImageLoaderListener{
void onImageLoader(Bitmap bitmap, String url);
}
}
ImageDownLoader中有幾個方法比較重要
- 首先我們需要重寫sizeOf(String key, Bitmap value)來計算圖片的大小，默認返回圖片的數量
- downloadImage(final String url, final onImageLoaderListener listener)先去LruCache查看Image,沒有再去手機緩存中查看，在沒有則開啟線程下載，這里我們提供了一個回調接口，回調方法中我們將Bitmap和圖片Url作為參數，String subUrl = url.replaceAll("[^\\w]", "") 我在代碼中注釋寫的比較清楚
-
showCacheBitmap(String url)方法，此方法在Adapter中的getView()當中調用，如果getView()中不調用此方法試試你就知道效果了
- ImageAdapter GridView的適配器類，主要是GridView滑動的時候取消下載任務，靜止的時候去下載當前顯示的item的圖片，其他也沒什么不同了
package com.example.asyncimageloader;
import android.content.Context;
import android.graphics.Bitmap;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import com.example.asyncimageloader.ImageDownLoader.onImageLoaderListener;
public class ImageAdapter extends BaseAdapter implements OnScrollListener{
/**
* 上下文對象的引用
*/
private Context context;
/**
* Image Url的數組
*/
private String [] imageThumbUrls;
/**
* GridView對象的應用
*/
private GridView mGridView;
/**
* Image 下載器
*/
private ImageDownLoader mImageDownLoader;
/**
* 記錄是否剛打開程序，用于解決進入程序不滾動屏幕，不會下載圖片的問題。
* 參考http://blog.csdn.net/guolin_blog/article/details/9526203#comments
*/
private boolean isFirstEnter = true;
/**
* 一屏中第一個item的位置
*/
private int mFirstVisibleItem;
/**
* 一屏中所有item的個數
*/
private int mVisibleItemCount;
public ImageAdapter(Context context, GridView mGridView, String [] imageThumbUrls){
this.context = context;
this.mGridView = mGridView;
this.imageThumbUrls = imageThumbUrls;
mImageDownLoader = new ImageDownLoader(context);
mGridView.setOnScrollListener(this);
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
//僅當GridView靜止時才去下載圖片，GridView滑動時取消所有正在下載的任務
if(scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE){
showImage(mFirstVisibleItem, mVisibleItemCount);
}else{
cancelTask();
}
}
/**
* GridView滾動的時候調用的方法，剛開始顯示GridView也會調用此方法
*/
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
mFirstVisibleItem = firstVisibleItem;
mVisibleItemCount = visibleItemCount;
// 因此在這里為首次進入程序開啟下載任務。
if(isFirstEnter && visibleItemCount > 0){
showImage(mFirstVisibleItem, mVisibleItemCount);
isFirstEnter = false;
}
}
@Override
public int getCount() {
return imageThumbUrls.length;
}
@Override
public Object getItem(int position) {
return imageThumbUrls[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView mImageView;
final String mImageUrl = imageThumbUrls[position];
if(convertView == null){
mImageView = new ImageView(context);
}else{
mImageView = (ImageView) convertView;
}
mImageView.setLayoutParams(new GridView.LayoutParams(150, 150));
mImageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
//給ImageView設置Tag,這里已經是司空見慣了
mImageView.setTag(mImageUrl);
/*******************************去掉下面這幾行試試是什么效果****************************/
Bitmap bitmap = mImageDownLoader.showCacheBitmap(mImageUrl.replaceAll("[^\\w]", ""));
if(bitmap != null){
mImageView.setImageBitmap(bitmap);
}else{
mImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.ic_empty));
}
/**********************************************************************************/
return mImageView;
}
/**
* 顯示當前屏幕的圖片，先會去查找LruCache，LruCache沒有就去sd卡或者手機目錄查找，在沒有就開啟線程去下載
* @param firstVisibleItem
* @param visibleItemCount
*/
private void showImage(int firstVisibleItem, int visibleItemCount){
Bitmap bitmap = null;
for(int i=firstVisibleItem; i<firstVisibleItem + visibleItemCount; i++){
String mImageUrl = imageThumbUrls[i];
final ImageView mImageView = (ImageView) mGridView.findViewWithTag(mImageUrl);
bitmap = mImageDownLoader.downloadImage(mImageUrl, new onImageLoaderListener() {
@Override
public void onImageLoader(Bitmap bitmap, String url) {
if(mImageView != null && bitmap != null){
mImageView.setImageBitmap(bitmap);
}
}
});
//if(bitmap != null){
// mImageView.setImageBitmap(bitmap);
//}else{
// mImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.ic_empty));
//}
}
}
/**
* 取消下載任務
*/
public void cancelTask(){
mImageDownLoader.cancelTask();
}
}
- MainActivity 里面一個GridView，然后提供一個系統菜單來刪除手機上的緩存圖片，直接上代碼，比較簡單所以里面也沒有注釋
package com.example.asyncimageloader;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.GridView;
import android.widget.Toast;
public class MainActivity extends Activity {
private GridView mGridView;
private String [] imageThumbUrls = Images.imageThumbUrls;
private ImageAdapter mImageAdapter;
private FileUtils fileUtils;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fileUtils = new FileUtils(this);
mGridView = (GridView) findViewById(R.id.gridView);
mImageAdapter = new ImageAdapter(this, mGridView, imageThumbUrls);
mGridView.setAdapter(mImageAdapter);
}
@Override
protected void onDestroy() {
mImageAdapter.cancelTask();
super.onDestroy();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
menu.add("刪除手機中圖片緩存");
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case 0:
fileUtils.deleteFile();
Toast.makeText(getApplication(), "清空緩存成功", Toast.LENGTH_SHORT).show();
break;
}
return super.onOptionsItemSelected(item);
}
}
- MainActivity的布局文件
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<GridView
android:id="@+id/gridView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:stretchMode="columnWidth"
android:columnWidth="90dip"
android:verticalSpacing="10dip"
android:horizontalSpacing="10dip"
android:cacheColorHint="@android:color/transparent"
android:numColumns="auto_fit" >
</GridView>
</RelativeLayout>
- 因為有網絡操作和對sd卡的操作，所以我們必須加上相對應的權限
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
好了，代碼就全部介紹完了，我們運行下程序看看效果，這里的效果是用一個線程下載圖片的效果，可能有一些不完整，想看看效果自己動手試試，郁悶，家里的網絡卡，gif的圖片出不來效果，只能明天上傳圖片啦,公司也上傳不了動畫效果，我去，那我就貼一張普通圖片，哈哈
好了，今天的講解到此結束，有疑問的朋友請在下面留言,源碼里面GridView的布局文件 columnWedth設置了120dip,有點丑，大家可以改成90dip
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