wemall-mobile是基于WeMall的android app商城,只需要在原商城目录下上传接口文件即可完成服务端的配置,客户端可定制修改。本文分享wemall app商城源码Android之ListView异步加载网络图片(优化缓存机制)代码信息,供技术员参考学习。
1、采用线程池
2、内存缓存+文件缓存
3、内存缓存中网上很多是采用SoftReference来防止堆溢出,这儿严格限制只能使用最大JVM内存的1/4
4、对下载的图片进行按比例缩放,以减少内存的消耗
具体的代码里面说明。先放上内存缓存类的代码MemoryCache.java:
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public class MemoryCache {
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private static final String TAG = "MemoryCache";
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// 放入缓存时是个同步操作
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// LinkedHashMap构造方法的最后一个参数true代表这个map里的元素将按照最近使用次数由少到多排列,即LRU
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// 这样的好处是如果要将缓存中的元素替换,则先遍历出最近最少使用的元素来替换以提高效率
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private Map<String, Bitmap> cache = Collections
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.synchronizedMap(new LinkedHashMap<String, Bitmap>(10, 1.5f, true));
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// 缓存中图片所占用的字节,初始0,将通过此变量严格控制缓存所占用的堆内存
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private long size = 0;// current allocated size
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// 缓存只能占用的最大堆内存
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private long limit = 1000000;// max memory in bytes
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public MemoryCache() {
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// use 25% of available heap size
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setLimit(Runtime.getRuntime().maxMemory() / 4);
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}
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public void setLimit(long new_limit) {
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limit = new_limit;
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Log.i(TAG, "MemoryCache will use up to " + limit / 1024. / 1024. + "MB");
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}
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public Bitmap get(String id) {
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try {
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if (!cache.containsKey(id))
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return null;
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return cache.get(id);
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} catch (NullPointerException ex) {
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return null;
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}
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}
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public void put(String id, Bitmap bitmap) {
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try {
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if (cache.containsKey(id))
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size -= getSizeInBytes(cache.get(id));
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cache.put(id, bitmap);
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size += getSizeInBytes(bitmap);
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checkSize();
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} catch (Throwable th) {
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th.printStackTrace();
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}
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}
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/**
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* 严格控制堆内存,如果超过将首先替换最近最少使用的那个图片缓存
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*
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*/
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private void checkSize() {
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Log.i(TAG, "cache size=" + size + " length=" + cache.size());
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if (size > limit) {
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// 先遍历最近最少使用的元素
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Iterator<Entry<String, Bitmap>> iter = cache.entrySet().iterator();
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while (iter.hasNext()) {
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Entry<String, Bitmap> entry = iter.next();
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size -= getSizeInBytes(entry.getValue());
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iter.remove();
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if (size <= limit)
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break;
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}
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Log.i(TAG, "Clean cache. New size " + cache.size());
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}
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}
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public void clear() {
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cache.clear();
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}
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/**
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* 图片占用的内存
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*
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* @param bitmap
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* @return
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*/
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long getSizeInBytes(Bitmap bitmap) {
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if (bitmap == null)
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return 0;
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return bitmap.getRowBytes() * bitmap.getHeight();
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}
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}
也可以使用SoftReference,代码会简单很多,但是我推荐上面的方法。
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public class MemoryCache {
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private Map<String, SoftReference<Bitmap>> cache = Collections
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.synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());
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public Bitmap get(String id) {
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if (!cache.containsKey(id))
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return null;
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SoftReference<Bitmap> ref = cache.get(id);
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return ref.get();
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}
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public void put(String id, Bitmap bitmap) {
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cache.put(id, new SoftReference<Bitmap>(bitmap));
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}
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public void clear() {
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cache.clear();
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}
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}
下面是文件缓存类的代码FileCache.java:
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public class FileCache {
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private File cacheDir;
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public FileCache(Context context) {
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// 如果有SD卡则在SD卡中建一个LazyList的目录存放缓存的图片
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// 没有SD卡就放在系统的缓存目录中
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if (android.os.Environment.getExternalStorageState().equals(
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android.os.Environment.MEDIA_MOUNTED))
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cacheDir = new File(
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android.os.Environment.getExternalStorageDirectory(),
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"LazyList");
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else
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cacheDir = context.getCacheDir();
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if (!cacheDir.exists())
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cacheDir.mkdirs();
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}
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public File getFile(String url) {
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// 将url的hashCode作为缓存的文件名
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String filename = String.valueOf(url.hashCode());
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// Another possible solution
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// String filename = URLEncoder.encode(url);
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File f = new File(cacheDir, filename);
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return f;
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}
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public void clear() {
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File[] files = cacheDir.listFiles();
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if (files == null)
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return;
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for (File f : files)
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f.delete();
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}
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}
最后最重要的加载图片的类,ImageLoader.java:
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public class ImageLoader {
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MemoryCache memoryCache = new MemoryCache();
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FileCache fileCache;
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private Map<ImageView, String> imageViews = Collections
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.synchronizedMap(new WeakHashMap<ImageView, String>());
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// 线程池
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ExecutorService executorService;
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public ImageLoader(Context context) {
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fileCache = new FileCache(context);
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executorService = Executors.newFixedThreadPool(5);
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}
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// 当进入listview时默认的图片,可换成你自己的默认图片
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final int stub_id = R.drawable.stub;
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// 最主要的方法
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public void DisplayImage(String url, ImageView imageView) {
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imageViews.put(imageView, url);
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// 先从内存缓存中查找
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Bitmap bitmap = memoryCache.get(url);
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if (bitmap != null)
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imageView.setImageBitmap(bitmap);
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else {
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// 若没有的话则开启新线程加载图片
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queuePhoto(url, imageView);
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imageView.setImageResource(stub_id);
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}
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}
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private void queuePhoto(String url, ImageView imageView) {
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PhotoToLoad p = new PhotoToLoad(url, imageView);
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executorService.submit(new PhotosLoader(p));
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}
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private Bitmap getBitmap(String url) {
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File f = fileCache.getFile(url);
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// 先从文件缓存中查找是否有
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Bitmap b = decodeFile(f);
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if (b != null)
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return b;
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// 最后从指定的url中下载图片
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try {
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Bitmap bitmap = null;
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URL imageUrl = new URL(url);
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HttpURLConnection conn = (HttpURLConnection) imageUrl
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.openConnection();
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conn.setConnectTimeout(30000);
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conn.setReadTimeout(30000);
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conn.setInstanceFollowRedirects(true);
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InputStream is = conn.getInputStream();
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OutputStream os = new FileOutputStream(f);
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CopyStream(is, os);
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os.close();
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bitmap = decodeFile(f);
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return bitmap;
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} catch (Exception ex) {
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ex.printStackTrace();
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return null;
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}
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}
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// decode这个图片并且按比例缩放以减少内存消耗,虚拟机对每张图片的缓存大小也是有限制的
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private Bitmap decodeFile(File f) {
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try {
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// decode image size
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BitmapFactory.Options o = new BitmapFactory.Options();
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o.inJustDecodeBounds = true;
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BitmapFactory.decodeStream(new FileInputStream(f), null, o);
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// Find the correct scale value. It should be the power of 2.
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final int REQUIRED_SIZE = 70;
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int width_tmp = o.outWidth, height_tmp = o.outHeight;
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int scale = 1;
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while (true) {
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if (width_tmp / 2 < REQUIRED_SIZE
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|| height_tmp / 2 < REQUIRED_SIZE)
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break;
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width_tmp /= 2;
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height_tmp /= 2;
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scale *= 2;
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}
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// decode with inSampleSize
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BitmapFactory.Options o2 = new BitmapFactory.Options();
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o2.inSampleSize = scale;
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return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
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} catch (FileNotFoundException e) {
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}
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return null;
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}
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// Task for the queue
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private class PhotoToLoad {
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public String url;
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public ImageView imageView;
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public PhotoToLoad(String u, ImageView i) {
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url = u;
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imageView = i;
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}
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}
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class PhotosLoader implements Runnable {
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PhotoToLoad photoToLoad;
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PhotosLoader(PhotoToLoad photoToLoad) {
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this.photoToLoad = photoToLoad;
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}
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@Override
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public void run() {
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if (imageViewReused(photoToLoad))
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return;
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Bitmap bmp = getBitmap(photoToLoad.url);
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memoryCache.put(photoToLoad.url, bmp);
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if (imageViewReused(photoToLoad))
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return;
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BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
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// 更新的操作放在UI线程中
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Activity a = (Activity) photoToLoad.imageView.getContext();
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a.runOnUiThread(bd);
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}
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}
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/**
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* 防止图片错位
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*
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* @param photoToLoad
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* @return
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*/
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boolean imageViewReused(PhotoToLoad photoToLoad) {
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String tag = imageViews.get(photoToLoad.imageView);
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if (tag == null || !tag.equals(photoToLoad.url))
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return true;
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return false;
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}
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// 用于在UI线程中更新界面
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class BitmapDisplayer implements Runnable {
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Bitmap bitmap;
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PhotoToLoad photoToLoad;
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public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
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bitmap = b;
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photoToLoad = p;
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}
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public void run() {
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if (imageViewReused(photoToLoad))
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return;
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if (bitmap != null)
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photoToLoad.imageView.setImageBitmap(bitmap);
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else
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photoToLoad.imageView.setImageResource(stub_id);
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}
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}
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public void clearCache() {
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memoryCache.clear();
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fileCache.clear();
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}
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public static void CopyStream(InputStream is, OutputStream os) {
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final int buffer_size = 1024;
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try {
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byte[] bytes = new byte[buffer_size];
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for (;;) {
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int count = is.read(bytes, 0, buffer_size);
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if (count == -1)
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break;
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os.write(bytes, 0, count);
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}
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} catch (Exception ex) {
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}
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}
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}
主要流程是先从内存缓存中查找,若没有再开线程,从文件缓存中查找都没有则从指定的url中查找,并对bitmap进行处理,最后通过下面方法对UI进行更新操作。
在你的程序中的基本用法:
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ImageLoader imageLoader=new ImageLoader(context);
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...
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imageLoader.DisplayImage(url, imageView);
比如你的放在你的ListView的adapter的getView()方法中,当然也适用于GridView。
wemall官网地址:
原文详情地址:
wemall doraemonAndroid app商城详情地址:
wemall 开源微商城 ,微信商城,商城源码,三级分销,微生鲜,微水果,微外卖,微订餐---专业的o2o系统
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