Android异步加载图片,并缓存到SD卡,这些都是一些代码片段,需要的时候可以用上,很不错的。
public class MemoryCache { private static final String TAG = "MemoryCache"; // Collections.synchronizedMap()的方法包装成一个线程安全的Map/Set private Map<String, Bitmap> cache = Collections .synchronizedMap(new LinkedHashMap<String, Bitmap>(10, 1.5f, true));// Last argument true for LRU ordering private long size = 0;// current allocated size private long limit = 1000000;// max memory in bytes public MemoryCache() { // use 25% of available heap size setLimit(Runtime.getRuntime().maxMemory() / 4); } public void setLimit(long new_limit) { limit = new_limit; Log.i(TAG, "MemoryCache will use up to " + limit / 1024. / 1024. + "MB"); } public Bitmap get(String id) { try { if (!cache.containsKey(id)) { return null; } // NullPointerException sometimes happen here // http://code.google.com/p/osmdroid/issues/detail?id=78 return cache.get(id); } catch (NullPointerException ex) { ex.printStackTrace(); return null; } } public void put(String id, Bitmap bitmap) { try { if (cache.containsKey(id)) { size -= getSizeInBytes(cache.get(id)); } cache.put(id, bitmap); size += getSizeInBytes(bitmap); checkSize(); } catch (Throwable th) { th.printStackTrace(); } } private void checkSize() { Log.i(TAG, "cache size=" + size + " length=" + cache.size()); if (size > limit) { Iterator<Entry<String, Bitmap>> iter = cache.entrySet().iterator();// least recently accessed item will be the first one iterated while (iter.hasNext()) { Entry<String, Bitmap> entry = iter.next(); size -= getSizeInBytes(entry.getValue()); iter.remove(); if (size <= limit) break; } Log.i(TAG, "Clean cache. New size " + cache.size()); } } public void clear() { try { // NullPointerException sometimes happen here // http://code.google.com/p/osmdroid/issues/detail?id=78 cache.clear(); size = 0; } catch (NullPointerException ex) { ex.printStackTrace(); } } long getSizeInBytes(Bitmap bitmap) { if (bitmap == null) return 0; return bitmap.getRowBytes() * bitmap.getHeight(); } }
下面是FileCache类:
public class FileCache { private File cacheDir; public FileCache(Context context) { // Find the dir to save cached images if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) cacheDir = new File( android.os.Environment.getExternalStorageDirectory(), "Cngolf"); else cacheDir = context.getCacheDir(); if (!cacheDir.exists()) cacheDir.mkdirs(); } public File getFile(String url) { // I identify images by hashcode. Not a perfect solution, good for the // demo. String filename = String.valueOf(url.hashCode()); // Another possible solution (thanks to grantland) // String filename = URLEncoder.encode(url); File f = new File(cacheDir, filename); return f; } public void clear() { File[] files = cacheDir.listFiles(); if (files == null) return; for (File f : files) f.delete(); } }
Utils类:
public class Utils { public static void CopyStream(InputStream is, OutputStream os) { final int buffer_size = 1024; try { byte[] bytes = new byte[buffer_size]; for (;;) { int count = is.read(bytes, 0, buffer_size); if (count == -1) break; os.write(bytes, 0, count); } } catch (Exception ex) { } } }
下面是非常重要的代码来的:
public class ImageLoader { MemoryCache memoryCache = new MemoryCache(); FileCache fileCache; private Map<ImageView, String> imageViews = Collections .synchronizedMap(new WeakHashMap<ImageView, String>()); ExecutorService executorService; Handler handler = new Handler();// handler to display images in UI thread public ImageLoader(Context context) { fileCache = new FileCache(context); executorService = Executors.newFixedThreadPool(5); } final int stub_id = R.drawable.stub; public void DisplayImage(String url, ImageView imageView) { imageViews.put(imageView, url); Bitmap bitmap = memoryCache.get(url); if (bitmap != null) imageView.setImageBitmap(bitmap); else { queuePhoto(url, imageView); imageView.setImageResource(stub_id); } } private void queuePhoto(String url, ImageView imageView) { PhotoToLoad p = new PhotoToLoad(url, imageView); executorService.submit(new PhotosLoader(p)); } private Bitmap getBitmap(String url) { File f = fileCache.getFile(url); // from SD cache Bitmap b = decodeFile(f); if (b != null) return b; // from web try { Bitmap bitmap = null; URL imageUrl = new URL(url); HttpURLConnection conn = (HttpURLConnection) imageUrl .openConnection(); conn.setConnectTimeout(30000); conn.setReadTimeout(30000); conn.setInstanceFollowRedirects(true); InputStream is = conn.getInputStream(); OutputStream os = new FileOutputStream(f); Utils.CopyStream(is, os); os.close(); conn.disconnect(); bitmap = decodeFile(f); return bitmap; } catch (Throwable ex) { ex.printStackTrace(); if (ex instanceof OutOfMemoryError) memoryCache.clear(); return null; } } // decodes image and scales it to reduce memory consumption private Bitmap decodeFile(File f) { try { // decode image size BitmapFactory.Options o = new BitmapFactory.Options(); o.inJustDecodeBounds = true; FileInputStream stream1 = new FileInputStream(f); BitmapFactory.decodeStream(stream1, null, o); stream1.close(); // Find the correct scale value. It should 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 *= 2; } // decode with inSampleSize BitmapFactory.Options o2 = new BitmapFactory.Options(); o2.inSampleSize = scale; FileInputStream stream2 = new FileInputStream(f); Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2); stream2.close(); return bitmap; } catch (FileNotFoundException e) { } catch (IOException e) { e.printStackTrace(); } return null; } // Task for the queue private class PhotoToLoad { public String url; public ImageView imageView; public PhotoToLoad(String u, ImageView i) { url = u; imageView = i; } } class PhotosLoader implements Runnable { PhotoToLoad photoToLoad; PhotosLoader(PhotoToLoad photoToLoad) { this.photoToLoad = photoToLoad; } @Override public void run() { try { if (imageViewReused(photoToLoad)) return; Bitmap bmp = getBitmap(photoToLoad.url); memoryCache.put(photoToLoad.url, bmp); if (imageViewReused(photoToLoad)) return; BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad); handler.post(bd); } catch (Throwable th) { th.printStackTrace(); } } } boolean imageViewReused(PhotoToLoad photoToLoad) { String tag = imageViews.get(photoToLoad.imageView); if (tag == null || !tag.equals(photoToLoad.url)) return true; return false; } // Used to display bitmap in the UI thread class BitmapDisplayer implements Runnable { Bitmap bitmap; PhotoToLoad photoToLoad; public BitmapDisplayer(Bitmap b, PhotoToLoad p) { bitmap = b; photoToLoad = p; } public void run() { if (imageViewReused(photoToLoad)) return; if (bitmap != null) photoToLoad.imageView.setImageBitmap(bitmap); else photoToLoad.imageView.setImageResource(stub_id); } } public void clearCache() { memoryCache.clear(); fileCache.clear(); } }
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