Android listview uses multithreading to asynchronously load images and Update views

I. asynchronous imageview loading class

Package COM. busap. netutils; import Java. lang. ref. softreference; import Java. util. hashmap; import Java. util. linkedhashmap; import Java. util. map. entry; import android. graphics. bitmap; import android. OS. handler; import android. util. log; import android. widget. imageview;/*** use multiple threads to asynchronously load images and update the view ** @ author Lizhen **/public final class asynimageloader {private loaderthread thread; // The thread private hashm that loads the image and sends a message to the update Interface AP <string, softreference <bitmap> imagecache; // image object cache, key: urlprivate handler of the image; // handler object public asynimageloader (handler) of the Interface Activity) {imagecache = new hashmap <string, softreference <bitmap> (); this. handler = handler;}/*** display the image in the specified imageview before loading, the image URL is saved in the tag of the view object ** @ Param imageview * view of the image to be displayed * @ Param defaultbitmap * load the default image object to be loaded */Public void loadbitmap (imageview Image View, bitmap defaultbitmap) {// URL of the image. This value may be changed to string url = (string) imageview during image loading. gettag (); If (imagecache. containskey (URL) {// determines whether softreference <bitmap> softreference = imagecache exists in the cache. get (URL); Bitmap bitmap = softreference. get (); If (Bitmap! = NULL) {// if the image object is not empty, you can mount and update the view and return the imageview. setimagebitmap (Bitmap); return;} else {// if it is empty, delete it from the cache (its bitmap object has been recycled and released and needs to be reloaded) log. E ("tag", "cache bitmap is null"); imagecache. remove (URL) ;}} imageview. setimagebitmap (defaultbitmap); // first, a prompt is displayed indicating that the image is being loaded if (thread = NULL) {// The loading thread does not exist and the thread has not started yet, you need to create a thread and start thread = new loaderthread (imageview, URL); thread. start ();} else {// If so, call the thread object to load the thread. load (imageview, URL) ;}/*** Release all bitmap objects in the cache and clear the cache */Public void releasebitmapcache () {If (imagecache! = NULL) {for (Entry <string, softreference <bitmap> entry: imagecache. entryset () {Bitmap bitmap = entry. getvalue (). get (); If (Bitmap! = NULL) {bitmap. recycle (); // release the bitmap object} imagecache. clear () ;}}/*** thread for loading and displaying images */private class loaderthread extends thread {javashashmap <string, imageview> mtaskmap; // The task chain private Boolean miswait of the Image view object to be loaded and displayed; // identifies whether the thread is in the waiting state public loaderthread (imageview, string URL) {mtaskmap = new linkedhashmap <string, imageview> (); mtaskmap. put (URL, imageview);}/*** process the update display of a view ** @ Param imageview */Public void load (imageview, string URL) {mtaskmap. remove (imageview); // It may be available in the task chain. You must delete mtaskmap first. put (URL, imageview); // Add it to the task if (miswait) {// This must be synchronized when the thread is waiting to wake up the thread to process the synchronized (this) of the task to be processed in the task queue {// This must be synchronized when calling the notify () of the object. policy () ;}}@ overridepublic void run () {While (mtaskmap. size ()> 0) {// when there is data in the queue, the thread will always run. once it enters, it must ensure that it will not jump out of the loop miswait = false; final string url = mtaskmap. keyset (). iterator (). next (); Final imageview = mtaskmap. remove (URL); If (imageview. gettag () = URL) {// determine whether the view is reused (once the imageview is reused, its tag value will be changed) Final Bitmap bitmap = myconnection. getbitmapbyurl (URL); // This method should load try {thread from the network or SD card. sleep (1000); // simulate the time when the network loads data} catch (interruptedexception E1) {e1.printstacktrace () ;}// put the loaded image into the cached map imagecache. put (URL, new softreference <bitmap> (Bitmap); If (url = imageview. gettag () {// judge whether the view has reused handler. post (New runnable () {// update the UI @ overridepublic void run () {imageview in the main thread through the message mechanism. setimagebitmap (Bitmap) ;}}}}if (mtaskmap. isempty () {// when there are no tasks to be processed in the task queue, the thread enters the waiting state try {miswait = true; // identifies the thread status, which must be in wait () synchronized (this) {This. wait (); // The guaranteed-performance thread enters the waiting state until a new task is added.} catch (interruptedexception e) {e. printstacktrace ();}}}}}}

Ii. Use

Handler handler;AsynImageLoader mImageAsynLoader;mImageAsynLoader.loadBitmap(discount_icon,defaultBitmap);