Asynchronous download of images and image caching

Functions:

The process is as follows:

Remoteimageviewactivity:

    public class RemoteImageViewActivity extends Activity {          /** Called when the activity is first created. */          @Override          public void onCreate(Bundle savedInstanceState) {              super.onCreate(savedInstanceState);              setContentView(R.layout.main);                    RemoteImageView img = (RemoteImageView) findViewById(R.id.remote_img);              img.setDefaultImage(R.drawable.ic_launcher);              img.setImageUrl("http://img2.kwcdn.kuwo.cn:81/star/albumcover/120/7/8/83787_1323997225.jpg");          }                @Override          protected void onPause() {              // TODO Auto-generated method stub              super.onPause();          }      }  

Imagecache:

Public class imagecache extends weakhashmap <string, bitmap> {/*** determines whether the URL exists * @ Param URL * @ return */Public Boolean iscached (string URL) {return containskey (URL) & get (URL )! = NULL ;}}

Remoteimageapplication:

    public class RemoteImageApplication extends Application {                public static final String TAG = "RemoteImageApplication";                private static RemoteImageApplication application;                private ImageCache mImageCache;                public SharedPreferences prefs = null;                          public static RemoteImageApplication getInstance() {              return application;          }                @Override          public void onCreate() {              // TODO Auto-generated method stub              super.onCreate();                    application = this;                    mImageCache = new ImageCache();                    prefs = PreferenceManager.getDefaultSharedPreferences(this);          }                public ImageCache getImageCache() {              return mImageCache;          }      }  

Remotesettings:

Public class remotesettings {public static final string cache_size = "cache_size"; // The image cache size is retained. If the size is exceeded, the cache is automatically cleared .}

Remoteimageview:

Public class remoteimageview extends imageview {private context mcontext; Private Static int mcachesize = 150; // set the cache size. Private Static final int max_failures = 3; // Number of download attempts private int mfailure; // Number of download attempts private string murl; // The current downloaded URL private string mcurrentlygrabbedurl; // URL private final static string jamendo_dir = "android/data/COM. teleca. jamendo "; // File Cache path. private Final Static long Mbit/s = 1073741824; Public remoteimageview (context, attributeset attrs, int defstyle) {super (context, ATT RS, defstyle); mcontext = context;} public remoteimageview (context, attributeset attrs) {super (context, attrs); mcontext = context;} public remoteimageview (context) {super (context); mcontext = context;}/*** sets the default image */Public void setdefaultimage (integer resid) {setimageresource (resid );} /*** set the image to be asynchronously loaded */Public void setimageurl (string URL) {// download failed to retry. If the number of retries exceeds the specified limit, directly Return. If (murl! = NULL & murl. Equals (URL) & (mcurrentlygrabbedurl = NULL | (mcurrentlygrabbedurl! = NULL &&! Mcurrentlygrabbedurl. equals (URL) {mfailure ++; If (mfailure> max_failures) {log. E (remoteimageapplication. tag, "failed to download the image address:" + URL); Return ;}} else {murl = URL; mfailure = 0 ;} imagecache = remoteimageapplication. getinstance (). getimagecache (); If (imagecache. iscached (URL) {setimagebitmap (imagecache. get (URL);} else {// If the cache does not exist in the memory, search for it from the file. string filename = converturltofilen Ame (URL); // process the file name string filepath = getdirectory (filename); // obtain the cache folder directory string pathfilename = filepath + "/" + filename; // file pathfile = new file (pathfilename); If (! Pathfile. exists () {try {pathfile. createnewfile ();} catch (ioexception e) {log. D (remoteimageapplication. tag, "failed to create image file:" + pathfilename) ;}} bitmap tbmp = bitmapfactory. decodefile (pathfilename); If (tbmp = NULL) {log. D (remoteimageapplication. tag, "image file does not exist, start to download"); try {New downloadtask(.exe cute (URL);} catch (rejectedexecutionexception e) {log. D (remoteimageapplication. tag, "Download failed") ;}} E LSE {log. I (remoteimageapplication. tag, "loading images from files"); remoteimageapplication. getinstance (). getimagecache (). put (URL, tbmp); this. setimagebitmap (tbmp);} updatecachesize (pathfilename); // check the file size to clear the cache .}} private void updatecachesize (string pathfilename) {// todo auto-generated method stub updatesizecache (pathfilename );} /*** check whether the file directory exceeds the specified cache size ** @ Param filename */private void updatesizeca Che (string pathfilename) {// todo auto-generated method stub mcachesize = preferencemanager. getdefasharsharedpreferences (mcontext ). getint (remotesettings. cache_size, 100); // read the set cache size. The foreground can dynamically set this value if (issdcardenable () {string extstoragedirectory = environment. getexternalstoragedirectory (). tostring (); // get the SD root path string dirpath = extstoragedirectory + "/" + jamendo_dir + "/imagecache"; file dirfil E = new file (dirpath); file [] files = dirfile. listfiles (); long dirsize = 0; For (File file: Files) {dirsize + = file. length () ;}if (dirsize> mcachesize * MB) {audio AchE () ;}}/ *** download image asynchronously ** @ classname: downloadtask * @ author Jiang Tao * @ version 1.0 5:06:21 */class downloadtask extends asynctask <string, void, string> {private string mtaskurl; private bitmap mbmp = NULL; @ override Public void onpreexecute () {// loaddefaultimage (); super. onpreexecute () ;}@ override Public String doinbackground (string... params) {mtaskurl = Params [0]; inputstream stream = NULL; Url imageurl; bitmap BMP = NULL; try {imageurl = new URL (mtaskurl); try {stream = imageurl. openstream (); BMP = bitmapfactory. decodestream (Stream); try {If (BMP! = NULL) {mbmp = BMP; remoteimageapplication. getinstance (). getimagecache (). put (mtaskurl, BMP); log. D (remoteimageapplication. tag, "image cached in application:" + mtaskurl) ;}} catch (nullpointerexception e) {log. W (remoteimageapplication. tag, "Download failed, image is empty:" + mtaskurl) ;}} catch (ioexception e) {log. W (remoteimageapplication. tag, "unable to load this URL:" + mtaskurl);} finally {try {If (stream! = NULL) {stream. close () ;}} catch (ioexception e) {}} catch (malformedurlexception e) {e. printstacktrace ();} return mtaskurl;} @ override public void onpostexecute (string URL) {super. onpostexecute (URL); bitmap BMP = remoteimageapplication. getinstance (). getimagecache (). get (URL); If (BMP = NULL) {log. W (remoteimageapplication. tag, "try to download again:" + URL); remoteimageview. this. setimageurl (URL );} Else {remoteimageview. this. setimagebitmap (BMP); mcurrentlygrabbedurl = URL; savebmptosd (mbmp, URL );}}}; /*** Save the image locally ** @ Param BM * @ Param URL */private void savebmptosd (Bitmap BM, string URL) {If (Bm = NULL) {return;} If (mcachesize = 0) {return;} string filename = converturltofilename (URL); string dir = getdirectory (filename ); file file = new file (DIR + "/" + filename); try {File. Createnewfile (); outputstream outstream = new fileoutputstream (File); BM. compress (bitmap. compressformat. JPEG, 100, outstream); outstream. flush (); outstream. close (); log. I (remoteimageapplication. tag, "image saved to SD card");} catch (filenotfoundexception e) {log. W (remoteimageapplication. tag, "file directory not found");} catch (ioexception e) {log. W (remoteimageapplication. tag, "Operation file error");}/*** name of the group spelling file, with the suffix replaced by dat, to prevent others from using The image manager searches for such images that are useless to them. ** @ Param URL * @ return */private string converturltofilename (string URL) {string filename = URL; filename = filename. replace ("http: //", ""); filename = filename. replace ("/",". "); filename = filename. replace (":",". "); filename = filename. replace ("jpg", "dat"); filename = filename. replace ("PNG", "dat"); Return filename;}/*** return the folder where the cached image is stored ** @ Param filename * @ return * /Private string getdirectory (string filename) {string extstoragedirectory = environment. getexternalstoragedirectory (). tostring (); // obtain the SD root path string dirpath = extstoragedirectory + "/" + jamendo_dir + "/imagecache"; file dirfile = new file (dirpath); If (! Dirfile. exists () {dirfile. mkdirs ();} return dirpath;}/*** clear cache */private void revoke AchE () {If (issdcardenable () {string extstoragedirectory = environment. getexternalstoragedirectory (). tostring (); // obtain the SD root path string dirpath = extstoragedirectory + "/" + jamendo_dir + "/imagecache"; file dir = new file (dirpath ); file [] files = dir. listfiles (); // obtain all files in this directory if (Files = NULL | files. length = 0) {return;} For (File file: Files) {file. delete ();} log. D (remoteimageapplication. tag, "cache cleared:" + dirpath) ;}/ *** determine whether the SD card is available */public static Boolean issdcardenable () {return environment. getexternalstoragestate (). equals (environment. media_mounted );}}

This article from: http://lewisliu.iteye.com/blog/1346820