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一、背景

  贝壳2.6.0版本使用Glide preload方法替换了部分显示图片的方式， 在灰度期间发现控件显示了错误的图片或者崩溃问题。

Fatal Exception: java.lang.RuntimeException:Canvas: trying to use a recycled bitmap android.graphics.Bitmap@25e89bf at android.graphics.Canvas.throwIfCannotDraw(Canvas.java:1271) at android.view.DisplayListCanvas.throwIfCannotDraw(DisplayListCanvas.java:257) at android.graphics.Canvas.drawBitmap(Canvas.java:1415) at com.bumptech.glide.load.resource.bitmap.GlideBitmapDrawable.draw(GlideBitmapDrawable.java:101)

二、原因分析

    Glide使用activityResources、LruResourceCache、LruBitmapPool等3级内存和文件缓存LazyDiskCacheProvider。

  activeResources是个Map， key值(EngineKey)根据10个参数组合生成，value是ResourceWeakReference类型； resource是EngineResource类并实现引用计数。

activeResources.put(key, new ResourceWeakReference(key, resource, getReferenceQueue()));

public void recycle() {    if (acquired > 0) {        throw new IllegalStateException("Cannot recycle a resource while it is still acquired");    }    if (isRecycled) {        throw new IllegalStateException("Cannot recycle a resource that has already been recycled");    }    isRecycled = true;    resource.recycle();  //实际上将Bitmap添加到BitmapPool} /** * Increments the number of consumers using the wrapped resource. Must be called on the main thread. * * 
 *     This must be called with a number corresponding to the number of new consumers each time new consumers *     begin using the wrapped resource. It is always safer to call acquire more often than necessary. Generally *     external users should never call this method, the framework will take care of this for you. * 
 */void acquire() {    if (isRecycled) {        throw new IllegalStateException("Cannot acquire a recycled resource");    }    if (!Looper.getMainLooper().equals(Looper.myLooper())) {        throw new IllegalThreadStateException("Must call acquire on the main thread");    }    ++acquired;} /** * Decrements the number of consumers using the wrapped resource. Must be called on the main thread. * * 
 *     This must only be called when a consumer that called the {@link #acquire()} method is now done with the *     resource. Generally external users should never callthis method, the framework will take care of this for *     you. * 
 */void release() {    if (acquired <= 0) {        throw new IllegalStateException("Cannot release a recycled or not yet acquired resource");    }    if (!Looper.getMainLooper().equals(Looper.myLooper())) {        throw new IllegalThreadStateException("Must call release on the main thread");    }    if (--acquired == 0) {        listener.onResourceReleased(key, this);     }}

LruResourceCache使用最近最少使用算法跟保存从activeResources移出的resource， 如果LruCache满了则移除记录并添加到LruBitmapPool。

LruBitmapPool的作用是缓存废弃的Bitmap（包括从activeResources或者LurResourcesCache移出的）， 每次解码图片时先从bitmappool找是否有合适的bitmap实例复用，找到了则从BitmapPool里移出，找不到则实例化个Bitmap对象。

                                                                                 into方式bitmap转换关系

                                                               使用BitmapPool

三、preload和into区别

  preload会创建PreloadTarget， 在回调onResourceReady时执行了Glide.clear(this),  将当前GlideDrawable从activeResources移动到LruResourcesCache。 即执行了cache.put(cacheKey, resource);

public final class PreloadTarget
   
     extends SimpleTarget
    
      {     /**     * Returns a PreloadTarget.     *     * @param width The width in pixels of the desired resource.     * @param height The height in pixels of the desired resource.     * @param 
     
       The type of the desired resource.     */    public static 
      
        PreloadTarget
       
         obtain(int width, int height) {        return new PreloadTarget
        
         (width, height); } private PreloadTarget(int width, int height) { super(width, height); } @Override public void onResourceReady(Z resource, GlideAnimation
          glideAnimation) { Glide.clear(this); }}
        
       
      
     
    
   

 划重点： 如果当前界面在onResourceReady回调函数里使用drawable刷新到界面， 那么可能导致crash或者渲染错误图片的问题。 原因是LruCache里缓存的图片可能被移出到BitmapPool； 而Glide在transform图片时会从BitmapPool里取Bitmap对象(UI显示错误的图片)， 也可能执行bitmap的recycle方法（程序崩溃）。  即在onResourceReady里使用的GlideDrawable内存区域可能在其它地方篡改。

into会创建GenericTarget， 在回调onResourceReady时

public final class GenericRequest
   
     implements Request, SizeReadyCallback,        ResourceCallback { ...public void onResourceReady(Resource
     resource) {    if (resource == null) {        onException(new Exception("Expected to receive a Resource
    
      with an object of " + transcodeClass                + " inside, but instead got null."));        return;    }     Object received = resource.get();    if (received == null || !transcodeClass.isAssignableFrom(received.getClass())) {        releaseResource(resource);        onException(new Exception("Expected to receive an object of " + transcodeClass                + " but instead got " + (received != null ? received.getClass() : "") + "{" + received + "}"                + " inside Resource{" + resource + "}."                + (received != null ? "" : " "                    + "To indicate failure return a null Resource object, "                    + "rather than a Resource object containing null data.")        ));        return;    }     if (!canSetResource()) {        releaseResource(resource);        // We can't set the status to complete before asking canSetResource().        status = Status.COMPLETE;        return;    }     onResourceReady(resource, (R) received);} /** * Internal {@link #onResourceReady(Resource)} where arguments are known to be safe. * * @param resource original {@link Resource}, never 
     null * @param result object returned by {@link Resource#get()}, checked for type and never 
     null */private void onResourceReady(Resource
      resource, R result) {    // We must call isFirstReadyResource before setting status.    boolean isFirstResource = isFirstReadyResource();    status = Status.COMPLETE;    this.resource = resource;     if (requestListener == null || !requestListener.onResourceReady(result, model, target, loadedFromMemoryCache,            isFirstResource)) {        GlideAnimation
     
       animation = animationFactory.build(loadedFromMemoryCache, isFirstResource);        target.onResourceReady(result, animation);  //执行GlideDrawbleImageViewTarget的setResource方法，即view.setImageDrawable    }     notifyLoadSuccess();     if (Log.isLoggable(TAG, Log.VERBOSE)) {        logV("Resource ready in " + LogTime.getElapsedMillis(startTime) + " size: "                + (resource.getSize() * TO_MEGABYTE) + " fromCache: " + loadedFromMemoryCache);    }}....  }
     
    
   

四、结论

      Glide的preload回调函数onResourceReady返回的resource并不可靠， 在使用时要新创建个实例或者保存成文件后使用它。

LJImageLoader.with(getContext()).url(ConstantUtil.URL_CDN_WALLET_REWARD_SELECTED)    .dontAnimate()    .listener(new ILoadListener() {      @Override public boolean onException(Exception e, String model) {        return false;      }       @Override public boolean onResourceReady(Drawable resource, String model) {        if (resource != null) {          Bitmap bmp = Tools.drawableToBitmap(resource);          if (bmp != null) {            rootView.setBackground(new BitmapDrawable(getResources(), bmp));          }        }        return false;      }    }).preload();

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