Android图片的异步加载，主要原理：
加载图片时先查看缓存中是否存在该图片，如果存在则返回该图片，否则先加载载一个默认的占位图片，同时创建一个通过网络获取图片的任务并添加，任务完成后发送消息给主线程更新界面。
使用方法：
[java] view plain copy AsynImageLoader asynImageLoader = new AsynImageLoader(); asynImageLoader.showImageAsyn(imageView, imageUrl, resId);
类代码：
[java] view plain copy package com.wangge.uumao.http; import java.lang.ref.SoftReference; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import android.graphics.Bitmap; import android.os.Handler; import android.os.Message; import android.util.Log; import android.widget.ImageView; import com.wangge.uumao.util.PicUtil; public class AsynImageLoader { private static final String TAG = "AsynImageLoader"; // 缓存下载过的图片的Map private Map<String, SoftReference<Bitmap>> caches; // 任务队列 private List<Task> taskQueue; private boolean isRunning = false; public AsynImageLoader(){ // 初始化变量 caches = new HashMap<String, SoftReference<Bitmap>>(); taskQueue = new ArrayList<AsynImageLoader.Task>(); // 启动图片下载线程 isRunning = true; new Thread(runnable).start(); } /** * * @param imageView 需要延迟加载图片的对象 * @param url 图片的URL地址 * @param resId 图片加载过程中显示的图片资源 */ public void showImageAsyn(ImageView imageView, String url, int resId){ imageView.setTag(url); Bitmap bitmap = loadImageAsyn(url, getImageCallback(imageView, resId)); if(bitmap == null){ imageView.setImageResource(resId); }else{ imageView.setImageBitmap(bitmap); } } public Bitmap loadImageAsyn(String path, ImageCallback callback){ // 判断缓存中是否已经存在该图片 if(caches.containsKey(path)){ // 取出软引用 SoftReference<Bitmap> rf = caches.get(path); // 通过软引用，获取图片 Bitmap bitmap = rf.get(); // 如果该图片已经被释放，则将该path对应的键从Map中移除掉 if(bitmap == null){ caches.remove(path); }else{ // 如果图片未被释放，直接返回该图片 Log.i(TAG, "return image in cache" + path); return bitmap; } }else{ // 如果缓存中不常在该图片，则创建图片下载任务 Task task = new Task(); task.path = path; task.callback = callback; Log.i(TAG, "new Task ," + path); if(!taskQueue.contains(task)){ taskQueue.add(task); // 唤醒任务下载队列 synchronized (runnable) { runnable.notify(); } } } // 缓存中没有图片则返回null return null; } /** * * @param imageView * @param resId 图片加载完成前显示的图片资源ID * @return */ private ImageCallback getImageCallback(final ImageView imageView, final int resId){ return new ImageCallback() { @Override public void loadImage(String path, Bitmap bitmap) { if(path.equals(imageView.getTag().toString())){ imageView.setImageBitmap(bitmap); }else{ imageView.setImageResource(resId); } } }; } private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { // 子线程中返回的下载完成的任务 Task task = (Task)msg.obj; // 调用callback对象的loadImage方法，并将图片路径和图片回传给adapter task.callback.loadImage(task.path, task.bitmap); } }; private Runnable runnable = new Runnable() { @Override public void run() { while(isRunning){ // 当队列中还有未处理的任务时，执行下载任务 while(taskQueue.size() > 0){ // 获取第一个任务，并将之从任务队列中删除 Task task = taskQueue.remove(0); // 将下载的图片添加到缓存 task.bitmap = PicUtil.getbitmap(task.path); caches.put(task.path, new SoftReference<Bitmap>(task.bitmap)); if(handler != null){ // 创建消息对象，并将完成的任务添加到消息对象中 Message msg = handler.obtainMessage(); msg.obj = task; // 发送消息回主线程 handler.sendMessage(msg); } } //如果队列为空,则令线程等待 synchronized (this) { try { this.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } } }; //回调接口 public interface ImageCallback{ void loadImage(String path, Bitmap bitmap); } class Task{ // 下载任务的下载路径 String path; // 下载的图片 Bitmap bitmap; // 回调对象 ImageCallback callback; @Override public boolean equals(Object o) { Task task = (Task)o; return task.path.equals(path); } } }最后附上PicUtil类的代码，之前忘了贴这个类的代码，不好意识了~~
[java] view plain copy public class PicUtil { private static final String TAG = "PicUtil"; /** * 根据一个网络连接(URL)获取bitmapDrawable图像 * * @param imageUri * @return */ public static BitmapDrawable getfriendicon(URL imageUri) { BitmapDrawable icon = null; try { HttpURLConnection hp = (HttpURLConnection) imageUri .openConnection(); icon = new BitmapDrawable(hp.getInputStream());// 将输入流转换成bitmap hp.disconnect();// 关闭连接 } catch (Exception e) { } return icon; } /** * 根据一个网络连接(String)获取bitmapDrawable图像 * * @param imageUri * @return */ public static BitmapDrawable getcontentPic(String imageUri) { URL imgUrl = null; try { imgUrl = new URL(imageUri); } catch (MalformedURLException e1) { e1.printStackTrace(); } BitmapDrawable icon = null; try { HttpURLConnection hp = (HttpURLConnection) imgUrl.openConnection(); icon = new BitmapDrawable(hp.getInputStream());// 将输入流转换成bitmap hp.disconnect();// 关闭连接 } catch (Exception e) { } return icon; } /** * 根据一个网络连接(URL)获取bitmap图像 * * @param imageUri * @return */ public static Bitmap getusericon(URL imageUri) { // 显示网络上的图片 URL myFileUrl = imageUri; Bitmap bitmap = null; try { HttpURLConnection conn = (HttpURLConnection) myFileUrl .openConnection(); conn.setDoInput(true); conn.connect(); InputStream is = conn.getInputStream(); bitmap = BitmapFactory.decodeStream(is); is.close(); } catch (IOException e) { e.printStackTrace(); } return bitmap; } /** * 根据一个网络连接(String)获取bitmap图像 * * @param imageUri * @return * @throws MalformedURLException */ public static Bitmap getbitmap(String imageUri) { // 显示网络上的图片 Bitmap bitmap = null; try { URL myFileUrl = new URL(imageUri); HttpURLConnection conn = (HttpURLConnection) myFileUrl .openConnection(); conn.setDoInput(true); conn.connect(); InputStream is = conn.getInputStream(); bitmap = BitmapFactory.decodeStream(is); is.close(); Log.i(TAG, "image download finished." + imageUri); } catch (IOException e) { e.printStackTrace(); return null; } return bitmap; } /** * 下载图片 同时写道本地缓存文件中 * * @param context * @param imageUri * @return * @throws MalformedURLException */ public static Bitmap getbitmapAndwrite(String imageUri) { Bitmap bitmap = null; try { // 显示网络上的图片 URL myFileUrl = new URL(imageUri); HttpURLConnection conn = (HttpURLConnection) myFileUrl .openConnection(); conn.setDoInput(true); conn.connect(); InputStream is = conn.getInputStream(); File cacheFile = FileUtil.getCacheFile(imageUri); BufferedOutputStream bos = null; bos = new BufferedOutputStream(new FileOutputStream(cacheFile)); Log.i(TAG, "write file to " + cacheFile.getCanonicalPath()); byte[] buf = new byte[1024]; int len = 0; // 将网络上的图片存储到本地 while ((len = is.read(buf)) > 0) { bos.write(buf, 0, len); } is.close(); bos.close(); // 从本地加载图片 bitmap = BitmapFactory.decodeFile(cacheFile.getCanonicalPath()); String name = MD5Util.MD5(imageUri); } catch (IOException e) { e.printStackTrace(); } return bitmap; } public static boolean downpic(String picName, Bitmap bitmap) { boolean nowbol = false; try { File saveFile = new File("/mnt/sdcard/download/weibopic/" + picName + ".png"); if (!saveFile.exists()) { saveFile.createNewFile(); } FileOutputStream saveFileOutputStream; saveFileOutputStream = new FileOutputStream(saveFile); nowbol = bitmap.compress(Bitmap.CompressFormat.PNG, 100, saveFileOutputStream); saveFileOutputStream.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } return nowbol; } public static void writeTofiles(Context context, Bitmap bitmap, String filename) { BufferedOutputStream outputStream = null; try { outputStream = new BufferedOutputStream(context.openFileOutput( filename, Context.MODE_PRIVATE)); bitmap.compress(Bitmap.CompressFormat.PNG, 100, outputStream); } catch (FileNotFoundException e) { e.printStackTrace(); } } /** * 将文件写入缓存系统中 * * @param filename * @param is * @return */ public static String writefile(Context context, String filename, InputStream is) { BufferedInputStream inputStream = null; BufferedOutputStream outputStream = null; try { inputStream = new BufferedInputStream(is); outputStream = new BufferedOutputStream(context.openFileOutput( filename, Context.MODE_PRIVATE)); byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) != -1) { outputStream.write(buffer, 0, length); } } catch (Exception e) { } finally { if (inputStream != null) { try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } } if (outputStream != null) { try { outputStream.flush(); outputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } return context.getFilesDir() + "/" + filename + ".jpg"; } // 放大缩小图片 public static Bitmap zoomBitmap(Bitmap bitmap, int w, int h) { int width = bitmap.getWidth(); int height = bitmap.getHeight(); Matrix matrix = new Matrix(); float scaleWidht = ((float) w / width); float scaleHeight = ((float) h / height); matrix.postScale(scaleWidht, scaleHeight); Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true); return newbmp; } // 将Drawable转化为Bitmap public static Bitmap drawableToBitmap(Drawable drawable) { int width = drawable.getIntrinsicWidth(); int height = drawable.getIntrinsicHeight(); Bitmap bitmap = Bitmap.createBitmap(width, height, drawable .getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888 : Bitmap.Config.RGB_565); Canvas canvas = new Canvas(bitmap); drawable.setBounds(0, 0, width, height); drawable.draw(canvas); return bitmap; } // 获得圆角图片的方法 public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) { if(bitmap == null){ return null; } Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Config.ARGB_8888); Canvas canvas = new Canvas(output); final int color = 0xff424242; final Paint paint = new Paint(); final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight()); final RectF rectF = new RectF(rect); paint.setAntiAlias(true); canvas.drawARGB(0, 0, 0, 0); paint.setColor(color); canvas.drawRoundRect(rectF, roundPx, roundPx, paint); paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN)); canvas.drawBitmap(bitmap, rect, rect, paint); return output; } // 获得带倒影的图片方法 public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) { final int reflectionGap = 4; int width = bitmap.getWidth(); int height = bitmap.getHeight(); Matrix matrix = new Matrix(); matrix.preScale(1, -1); Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 0, height / 2, width, height / 2, matrix, false); Bitmap bitmapWithReflection = Bitmap.createBitmap(width, (height + height / 2), Config.ARGB_8888); Canvas canvas = new Canvas(bitmapWithReflection); canvas.drawBitmap(bitmap, 0, 0, null); Paint deafalutPaint = new Paint(); canvas.drawRect(0, height, width, height + reflectionGap, deafalutPaint); canvas.drawBitmap(reflectionImage, 0, height + reflectionGap, null); Paint paint = new Paint(); LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0, bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff, 0x00ffffff, TileMode.CLAMP); paint.setShader(shader); // Set the Transfer mode to be porter duff and destination in paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN)); // Draw a rectangle using the paint with our linear gradient canvas.drawRect(0, height, width, bitmapWithReflection.getHeight() + reflectionGap, paint); return bitmapWithReflection; } }FileUtil
[java] view plain copy package com.wangge.coupon.util; import java.io.File; import java.io.IOException; import android.os.Environment; import android.util.Log; import com.wangge.coupon.http.AsynImageLoader; public class FileUtil { private static final String TAG = "FileUtil"; public static File getCacheFile(String imageUri){ File cacheFile = null; try { if (Environment.getExternalStorageState().equals( Environment.MEDIA_MOUNTED)) { File sdCardDir = Environment.getExternalStorageDirectory(); String fileName = getFileName(imageUri); File dir = new File(sdCardDir.getCanonicalPath() + AsynImageLoader.CACHE_DIR); if (!dir.exists()) { dir.mkdirs(); } cacheFile = new File(dir, fileName); Log.i(TAG, "exists:" + cacheFile.exists() + ",dir:" + dir + ",file:" + fileName); } } catch (IOException e) { e.printStackTrace(); Log.e(TAG, "getCacheFileError:" + e.getMessage()); } return cacheFile; } public static String getFileName(String path) { int index = path.lastIndexOf("/"); return path.substring(index + 1); } }转载于:https://www.cnblogs.com/dongdong230/archive/2013/05/16/4183148.html
相关资源：Android异步加载图片例子