Android Volley图片加载功能详解

/** 网络图片请求类. */@SuppressWarnings("unused")public class ImageRequest extends Request<Bitmap> {  /** 默认图片获取的超时时间(单位:毫秒) */  public static final int DEFAULT_IMAGE_REQUEST_MS = 1000;  /** 默认图片获取的重试次数. */  public static final int DEFAULT_IMAGE_MAX_RETRIES = 2;  private final Response.Listener<Bitmap> mListener;  private final Bitmap.Config mDecodeConfig;  private final int mMaxWidth;  private final int mMaxHeight;  private ImageView.ScaleType mScaleType;  /** Bitmap解析同步锁,保证同一时间只有一个Bitmap被load到内存进行解析,防止OOM. */  private static final Object sDecodeLock = new Object();  /**   * 构造一个网络图片请求.   * @param url 图片的url地址.   * @param listener 请求成功用户设置的回调接口.   * @param maxWidth 图片的最大宽度.   * @param maxHeight 图片的最大高度.   * @param scaleType 图片缩放类型.   * @param decodeConfig 解析bitmap的配置.   * @param errorListener 请求失败用户设置的回调接口.   */  public ImageRequest(String url, Response.Listener<Bitmap> listener, int maxWidth, int maxHeight,            ImageView.ScaleType scaleType, Bitmap.Config decodeConfig,            Response.ErrorListener errorListener) {    super(Method.GET, url, errorListener);    mListener = listener;    mDecodeConfig = decodeConfig;    mMaxWidth = maxWidth;    mMaxHeight = maxHeight;    mScaleType = scaleType;  }  /** 设置网络图片请求的优先级. */  @Override  public Priority getPriority() {    return Priority.LOW;  }  @Override  protected Response<Bitmap> parseNetworkResponse(NetworkResponse response) {    synchronized (sDecodeLock) {      try {        return doParse(response);      } catch (OutOfMemoryError e) {        return Response.error(new VolleyError(e));      }    }  }  private Response<Bitmap> doParse(NetworkResponse response) {    byte[] data = response.data;    BitmapFactory.Options decodeOptions = new BitmapFactory.Options();    Bitmap bitmap;    if (mMaxWidth == 0 && mMaxHeight == 0) {      decodeOptions.inPreferredConfig = mDecodeConfig;      bitmap = BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);    } else {      // 获取网络图片的真实尺寸.      decodeOptions.inJustDecodeBounds = true;      BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);      int actualWidth = decodeOptions.outWidth;      int actualHeight = decodeOptions.outHeight;      int desiredWidth = getResizedDimension(mMaxWidth, mMaxHeight,          actualWidth, actualHeight, mScaleType);      int desireHeight = getResizedDimension(mMaxWidth, mMaxHeight,          actualWidth, actualHeight, mScaleType);      decodeOptions.inJustDecodeBounds = false;      decodeOptions.inSampleSize =          findBestSampleSize(actualWidth, actualHeight, desiredWidth, desireHeight);      Bitmap tempBitmap = BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);      if (tempBitmap != null && (tempBitmap.getWidth() > desiredWidth ||          tempBitmap.getHeight() > desireHeight)) {        bitmap = Bitmap.createScaledBitmap(tempBitmap, desiredWidth, desireHeight, true);        tempBitmap.recycle();      } else {        bitmap = tempBitmap;      }    }    if (bitmap == null) {      return Response.error(new VolleyError(response));    } else {      return Response.success(bitmap, HttpHeaderParser.parseCacheHeaders(response));    }  }  static int findBestSampleSize(      int actualWidth, int actualHeight, int desiredWidth, int desireHeight) {    double wr = (double) actualWidth / desiredWidth;    double hr = (double) actualHeight / desireHeight;    double ratio = Math.min(wr, hr);    float n = 1.0f;    while ((n * 2) <= ratio) {      n *= 2;    }    return (int) n;  }  /** 根据ImageView的ScaleType设置图片的大小. */  private static int getResizedDimension(int maxPrimary, int maxSecondary, int actualPrimary,                      int actualSecondary, ImageView.ScaleType scaleType) {    // 如果没有设置ImageView的最大值,则直接返回网络图片的真实大小.    if ((maxPrimary == 0) && (maxSecondary == 0)) {      return actualPrimary;    }    // 如果ImageView的ScaleType为FIX_XY,则将其设置为图片最值.    if (scaleType == ImageView.ScaleType.FIT_XY) {      if (maxPrimary == 0) {        return actualPrimary;      }      return maxPrimary;    }    if (maxPrimary == 0) {      double ratio = (double)maxSecondary / (double)actualSecondary;      return (int)(actualPrimary * ratio);    }    if (maxSecondary == 0) {      return maxPrimary;    }    double ratio = (double) actualSecondary / (double) actualPrimary;    int resized = maxPrimary;    if (scaleType == ImageView.ScaleType.CENTER_CROP) {      if ((resized * ratio) < maxSecondary) {        resized = (int)(maxSecondary / ratio);      }      return resized;    }    if ((resized * ratio) > maxSecondary) {      resized = (int)(maxSecondary / ratio);    }    return resized;  }  @Override  protected void deliverResponse(Bitmap response) {    mListener.onResponse(response);  }}

ImageLoader imageLoader = new ImageLoader(queue, new ImageCache() {  @Override  public void putBitmap(String url, Bitmap bitmap) {}  @Override  public Bitmap getBitmap(String url) { return null; }});

@SuppressWarnings({"unused", "StringBufferReplaceableByString"})public class ImageLoader {  /**   * 关联用来调用ImageLoader的RequestQueue.   */  private final RequestQueue mRequestQueue;  /** 图片内存缓存接口实现类. */  private final ImageCache mCache;  /** 存储同一时间执行的相同CacheKey的BatchedImageRequest集合. */  private final HashMap<String, BatchedImageRequest> mInFlightRequests =      new HashMap<String, BatchedImageRequest>();  private final HashMap<String, BatchedImageRequest> mBatchedResponses =      new HashMap<String, BatchedImageRequest>();  /** 获取主线程的Handler. */  private final Handler mHandler = new Handler(Looper.getMainLooper());  private Runnable mRunnable;  /** 定义图片K1缓存接口,即将图片的内存缓存工作交给用户来实现. */  public interface ImageCache {    Bitmap getBitmap(String url);    void putBitmap(String url, Bitmap bitmap);  }  /** 构造一个ImageLoader. */  public ImageLoader(RequestQueue queue, ImageCache imageCache) {    mRequestQueue = queue;    mCache = imageCache;  }  /** 构造网络图片请求成功和失败的回调接口. */  public static ImageListener getImageListener(final ImageView view, final int defaultImageResId,                         final int errorImageResId) {    return new ImageListener() {      @Override      public void onResponse(ImageContainer response, boolean isImmediate) {        if (response.getBitmap() != null) {          view.setImageBitmap(response.getBitmap());        } else if (defaultImageResId != 0) {          view.setImageResource(defaultImageResId);        }      }      @Override      public void onErrorResponse(VolleyError error) {        if (errorImageResId != 0) {          view.setImageResource(errorImageResId);        }      }    };  }  public ImageContainer get(String requestUrl, ImageListener imageListener,                int maxWidth, int maxHeight, ScaleType scaleType) {    // 判断当前方法是否在UI线程中执行.如果不是,则抛出异常.    throwIfNotOnMainThread();    final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight, scaleType);    // 从L1级缓存中根据key获取对应的Bitmap.    Bitmap cacheBitmap = mCache.getBitmap(cacheKey);    if (cacheBitmap != null) {      // L1缓存命中,通过缓存命中的Bitmap构造ImageContainer,并调用imageListener的响应成功接口.      ImageContainer container = new ImageContainer(cacheBitmap, requestUrl, null, null);      // 注意:因为目前是在UI线程中,因此这里是调用onResponse方法,并非回调.      imageListener.onResponse(container, true);      return container;    }    ImageContainer imageContainer =        new ImageContainer(null, requestUrl, cacheKey, imageListener);    // L1缓存命中失败,则先需要对ImageView设置默认图片.然后通过子线程拉取网络图片,进行显示.    imageListener.onResponse(imageContainer, true);    // 检查cacheKey对应的ImageRequest请求是否正在运行.    BatchedImageRequest request = mInFlightRequests.get(cacheKey);    if (request != null) {      // 相同的ImageRequest正在运行,不需要同时运行相同的ImageRequest.      // 只需要将其对应的ImageContainer加入到BatchedImageRequest的mContainers集合中.      // 当正在执行的ImageRequest结束后,会查看当前有多少正在阻塞的ImageRequest,      // 然后对其mContainers集合进行回调.      request.addContainer(imageContainer);      return imageContainer;    }    // L1缓存没命中,还是需要构造ImageRequest,通过RequestQueue的调度来获取网络图片    // 获取方法可能是:L2缓存(ps:Disk缓存)或者HTTP网络请求.    Request<Bitmap> newRequest =        makeImageRequest(requestUrl, maxWidth, maxHeight, scaleType, cacheKey);    mRequestQueue.add(newRequest);    mInFlightRequests.put(cacheKey, new BatchedImageRequest(newRequest, imageContainer));    return imageContainer;  }  /** 构造L1缓存的key值. */  private String getCacheKey(String url, int maxWidth, int maxHeight, ScaleType scaleType) {    return new StringBuilder(url.length() + 12).append("#W").append(maxWidth)        .append("#H").append(maxHeight).append("#S").append(scaleType.ordinal()).append(url)        .toString();  }  public boolean isCached(String requestUrl, int maxWidth, int maxHeight) {    return isCached(requestUrl, maxWidth, maxHeight, ScaleType.CENTER_INSIDE);  }  private boolean isCached(String requestUrl, int maxWidth, int maxHeight, ScaleType scaleType) {    throwIfNotOnMainThread();    String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight, scaleType);    return mCache.getBitmap(cacheKey) != null;  }  /** 当L1缓存没有命中时,构造ImageRequest,通过ImageRequest和RequestQueue获取图片. */  protected Request<Bitmap> makeImageRequest(final String requestUrl, int maxWidth, int maxHeight,                        ScaleType scaleType, final String cacheKey) {    return new ImageRequest(requestUrl, new Response.Listener<Bitmap>() {      @Override      public void onResponse(Bitmap response) {        onGetImageSuccess(cacheKey, response);      }    }, maxWidth, maxHeight, scaleType, Bitmap.Config.RGB_565, new Response.ErrorListener() {      @Override      public void onErrorResponse(VolleyError error) {        onGetImageError(cacheKey, error);      }    });  }  /** 图片请求失败回调.运行在UI线程中. */  private void onGetImageError(String cacheKey, VolleyError error) {    BatchedImageRequest request = mInFlightRequests.remove(cacheKey);    if (request != null) {      request.setError(error);      batchResponse(cacheKey, request);    }  }  /** 图片请求成功回调.运行在UI线程中. */  protected void onGetImageSuccess(String cacheKey, Bitmap response) {    // 增加L1缓存的键值对.    mCache.putBitmap(cacheKey, response);    // 同一时间内最初的ImageRequest执行成功后,回调这段时间阻塞的相同ImageRequest对应的成功回调接口.    BatchedImageRequest request = mInFlightRequests.remove(cacheKey);    if (request != null) {      request.mResponseBitmap = response;      // 将阻塞的ImageRequest进行结果分发.      batchResponse(cacheKey, request);    }  }  private void batchResponse(String cacheKey, BatchedImageRequest request) {    mBatchedResponses.put(cacheKey, request);    if (mRunnable == null) {      mRunnable = new Runnable() {        @Override        public void run() {          for (BatchedImageRequest bir : mBatchedResponses.values()) {            for (ImageContainer container : bir.mContainers) {              if (container.mListener == null) {                continue;              }              if (bir.getError() == null) {                container.mBitmap = bir.mResponseBitmap;                container.mListener.onResponse(container, false);              } else {                container.mListener.onErrorResponse(bir.getError());              }            }          }          mBatchedResponses.clear();          mRunnable = null;        }      };      // Post the runnable      mHandler.postDelayed(mRunnable, 100);    }  }  private void throwIfNotOnMainThread() {    if (Looper.myLooper() != Looper.getMainLooper()) {      throw new IllegalStateException("ImageLoader must be invoked from the main thread.");    }  }  /** 抽象出请求成功和失败的回调接口.默认可以使用Volley提供的ImageListener. */  public interface ImageListener extends Response.ErrorListener {    void onResponse(ImageContainer response, boolean isImmediate);  }  /** 网络图片请求的承载对象. */  public class ImageContainer {    /** ImageView需要加载的Bitmap. */    private Bitmap mBitmap;    /** L1缓存的key */    private final String mCacheKey;    /** ImageRequest请求的url. */    private final String mRequestUrl;    /** 图片请求成功或失败的回调接口类. */    private final ImageListener mListener;    public ImageContainer(Bitmap bitmap, String requestUrl, String cacheKey,               ImageListener listener) {      mBitmap = bitmap;      mRequestUrl = requestUrl;      mCacheKey = cacheKey;      mListener = listener;    }    public void cancelRequest() {      if (mListener == null) {        return;      }      BatchedImageRequest request = mInFlightRequests.get(mCacheKey);      if (request != null) {        boolean canceled = request.removeContainerAndCancelIfNecessary(this);        if (canceled) {          mInFlightRequests.remove(mCacheKey);        }      } else {        request = mBatchedResponses.get(mCacheKey);        if (request != null) {          request.removeContainerAndCancelIfNecessary(this);          if (request.mContainers.size() == 0) {            mBatchedResponses.remove(mCacheKey);          }        }      }    }    public Bitmap getBitmap() {      return mBitmap;    }    public String getRequestUrl() {      return mRequestUrl;    }  }  /**   * CacheKey相同的ImageRequest请求抽象类.   * 判定两个ImageRequest相同包括:   * 1. url相同.   * 2. maxWidth和maxHeight相同.   * 3. 显示的scaleType相同.   * 同一时间可能有多个相同CacheKey的ImageRequest请求,由于需要返回的Bitmap都一样,所以用BatchedImageRequest   * 来实现该功能.同一时间相同CacheKey的ImageRequest只能有一个.   * 为什么不使用RequestQueue的mWaitingRequestQueue来实现该功能?   * 答:是因为仅靠URL是没法判断两个ImageRequest相等的.   */  private class BatchedImageRequest {    /** 对应的ImageRequest请求. */    private final Request<?> mRequest;    /** 请求结果的Bitmap对象. */    private Bitmap mResponseBitmap;    /** ImageRequest的错误. */    private VolleyError mError;    /** 所有相同ImageRequest请求结果的封装集合. */    private final LinkedList<ImageContainer> mContainers = new LinkedList<ImageContainer>();    public BatchedImageRequest(Request<?> request, ImageContainer container) {      mRequest = request;      mContainers.add(container);    }    public VolleyError getError() {      return mError;    }    public void setError(VolleyError error) {      mError = error;    }    public void addContainer(ImageContainer container) {      mContainers.add(container);    }    public boolean removeContainerAndCancelIfNecessary(ImageContainer container) {      mContainers.remove(container);      if (mContainers.size() == 0) {        mRequest.cancel();        return true;      }      return false;    }  }}

 private final HashMap<String, BatchedImageRequest> mBatchedResponses =    new HashMap<String, BatchedImageRequest>();

  protected void onGetImageSuccess(String cacheKey, Bitmap response) {    // 增加L1缓存的键值对.    mCache.putBitmap(cacheKey, response);    // 同一时间内最初的ImageRequest执行成功后,回调这段时间阻塞的相同ImageRequest对应的成功回调接口.    BatchedImageRequest request = mInFlightRequests.remove(cacheKey);    if (request != null) {      request.mResponseBitmap = response;      // 将阻塞的ImageRequest进行结果分发.      batchResponse(cacheKey, request);    }  }

  private void batchResponse(String cacheKey, BatchedImageRequest request) {    mBatchedResponses.put(cacheKey, request);    if (mRunnable == null) {      mRunnable = new Runnable() {        @Override        public void run() {          for (BatchedImageRequest bir : mBatchedResponses.values()) {            for (ImageContainer container : bir.mContainers) {              if (container.mListener == null) {                continue;              }              if (bir.getError() == null) {                container.mBitmap = bir.mResponseBitmap;                container.mListener.onResponse(container, false);              } else {                container.mListener.onErrorResponse(bir.getError());              }            }          }          mBatchedResponses.clear();          mRunnable = null;        }      };      // Post the runnable      mHandler.postDelayed(mRunnable, 100);    }  }

  private void batchResponse(String cacheKey, BatchedImageRequest request) {    if (mRunnable == null) {      mRunnable = new Runnable() {        @Override        public void run() {          for (ImageContainer container : request.mContainers) {            if (container.mListener == null) {              continue;            }            if (request.getError() == null) {              container.mBitmap = request.mResponseBitmap;              container.mListener.onResponse(container, false);            } else {              container.mListener.onErrorResponse(request.getError());            }          }          mRunnable = null;        }      };      // Post the runnable      mHandler.postDelayed(mRunnable, 100);    }  }

import android.graphics.Bitmap;import android.support.v4.util.LruCache;/** Lru算法的L1缓存实现类. */@SuppressWarnings("unused")public class ImageLruCache implements ImageLoader.ImageCache {  private LruCache<String, Bitmap> mLruCache;  public ImageLruCache() {    this((int) Runtime.getRuntime().maxMemory() / 8);  }  public ImageLruCache(final int cacheSize) {    createLruCache(cacheSize);  }  private void createLruCache(final int cacheSize) {    mLruCache = new LruCache<String, Bitmap>(cacheSize) {      @Override      protected int sizeOf(String key, Bitmap value) {        return value.getRowBytes() * value.getHeight();      }    };  }  @Override  public Bitmap getBitmap(String url) {    return mLruCache.get(url);  }  @Override  public void putBitmap(String url, Bitmap bitmap) {    mLruCache.put(url, bitmap);  }}