[Android] asynchronously loading images-Good idea

Import Java. io. file; import Java. io. fileinputstream; import Java. io. filenotfoundexception; import Java. io. fileoutputstream; import Java. io. inputstream; import Java. io. outputstream; import java.net. URL; import Java. util. hashmap; import Java. util. stack; import android. app. activity; import android. content. context; import android. graphics. bitmap; import android. graphics. bitmapfactory; import android. widget. imagevie W;/*** @ author fed * an asynchronous image loading class written by foreigners. You can change it to any adapter baseadapyer. * ** Remember to add permissions, access the Internet, and write external memory (SD card, etc.) * <uses-Permission Android: Name = "android. permission. internet "/> <uses-Permission Android: Name =" android. permission. write_external_storage "/> */public class imageloader {// The simplest in-memory cache implementation. this shoshould be replaced with // something like softreference or bitmapoptions. inpurgeable (since 1.6) Private hashmap <string, bitmap> cache = new has Hmap <string, bitmap> (); photosqueue = new photosqueue (); // task for the queueprivate class phototoload {Public String URL; Public imageview; Public phototoload (string U, imageview I) {url = u; imageview = I;} private file cachedir; Public imageloader (context) {// make the background thead low priority. this way it will not affect // The UI implements cephotoloaderthread. setpr Iority (thread. norm_priority-1); // find the Dir to save cached imagesif (Android. OS. environment. getexternalstoragestate (). equals (Android. OS. environment. media_mounted) cachedir = new file (Android. OS. environment. getexternalstoragedirectory (), "lazylist"); elsecachedir = context. getcachedir (); If (! Cachedir. exists () cachedir. mkdirs ();} final int stub_id = R. drawable. icon; Public void displayimage (string URL, activity, imageview) {If (cache. containskey (URL) imageview. setimagebitmap (cache. get (URL); else {queuephoto (URL, activity, imageview); imageview. setimageresource (stub_id);} private void queuephoto (string URL, activity, imageview) {// This imageview may be Used for other images before. so there may be // some old tasks in the queue. we need to discard them. photosqueue. clean (imageview); phototoload P = new phototoload (URL, imageview); synchronized (photosqueue. photostoload) {photosqueue. photostoload. push (p); photosqueue. photostoload. policyall ();} // start thread if it's not started yetif (photoloaderthread. getstate () = thread. state. new) photoloaderthread. Start ();} private bitmap getbitmap (string URL) {// I identify images by hashcode. not a perfect solution, good for the // demo. string filename = string. valueof (URL. hashcode (); file F = new file (cachedir, filename); // from SD cachebitmap B = decodefile (f); If (B! = NULL) return B; // from webtry {Bitmap bitmap = NULL; inputstream is = new URL (URL ). openstream (); outputstream OS = new fileoutputstream (f); utils. copystream (is, OS); OS. close (); bitmap = decodefile (f); Return bitmap;} catch (exception ex) {ex. printstacktrace (); return NULL ;}// decodes image and scales it to reduce memory consumptionprivate bitmap decodefile (file F) {try {// decode image sizebitmapfactor Y. options o = new bitmapfactory. options (); O. injustdecodebounds = true; bitmapfactory. decodestream (New fileinputstream (F), null, O); // find the correct scale value. it shoshould be the power of 2. final int required_size = 70; int width_tmp = O. outwidth, height_tmp = O. outheight; int scale = 1; while (true) {If (width_tmp/2 <required_size | height_tmp/2 <required_size) break; width_tmp/= 2; height_tmp // = 2; scale ++;} // decode with insamplesizebitmapfactory. options O2 = new bitmapfactory. options (); o2.insamplesize = scale; return bitmapfactory. decodestream (New fileinputstream (F), null, O2);} catch (filenotfoundexception e) {} return NULL;} public void stopthread () {photoloaderthread. interrupt ();} // stores list of photos to downloadclass photosqueue {private stack <phototoload> photostoload = new stack <Phototoload> (); // removes all instances of this imageviewpublic void clean (imageview image) {for (Int J = 0; j <photostoload. size ();) {If (photostoload. get (j ). imageview = image) photostoload. remove (j); else ++ J ;}} class photosloader extends thread {@ overridepublic void run () {try {While (true) {// thread waits until there are any images to load in the // queueif (photosqueue. photostoload. size () = 0) synchronized (photosqueue. photostoload) {photosqueue. photostoload. Wait () ;}if (photosqueue. photostoload. Size ()! = 0) {phototoload; synchronized (photosqueue. photostoload) {phototoload = photosqueue. photostoload. pop ();} bitmap BMP = getbitmap (phototoload. URL); cache. put (phototoload. URL, BMP); If (string) phototoload. imageview. gettag ()). equals (phototoload. URL) {bitmapdisplayer BD = new bitmapdisplayer (BMP, phototoload. imageview); Activity A = (activity) phototoload. imageview. getcontext ();. runonuithre AD (BD) ;}} if (thread. interrupted () break;} catch (interruptedexception e) {// allow thread to exit }} photosloader photoloaderthread = new photosloader (); // used to display bitmap in the UI threadclass bitmapdisplayer implements runnable {Bitmap bitmap; imageview; Public bitmapdisplayer (Bitmap B, imageview I) {bitmap = B; imageview = I ;} public void run () {If (Bitmap! = NULL) imageview. setimagebitmap (Bitmap); elseimageview. setimageresource (stub_id) ;}} public void receivache () {// clear memory cachecache. clear (); // clear SD cachefile [] files = cachedir. listfiles (); For (file F: Files) F. delete ();}}