Android知识Android开发经验谈Android面试二

从源码角度深入理解Glide（下）

2019-02-19  本文已影响5人  maoqitian
glide_logo.png

上两篇文章从源码角度深入理解Glide（上）和从源码角度深入理解Glide（中）中，我们已经把Glide加载图片的基本流程走了一遍，想必你已经对Glide的加载原理有了新的认识并且见识到了Glide源码的复杂逻辑，在我们感叹Glide源码复杂的同时我们也忽略了Glide加载图片过程的其它细节，特别是缓存方面，我们在上一篇文章中对于缓存的处理都是跳过的，这一篇文章我们就从Glide的缓存开始再次对Glide进行深入理解。

Glide缓存

缓存的key

/**Key 接口*/
public interface Key {
  String STRING_CHARSET_NAME = "UTF-8";
  Charset CHARSET = Charset.forName(STRING_CHARSET_NAME);
  void updateDiskCacheKey(@NonNull MessageDigest messageDigest);
  @Override
  boolean equals(Object o);
  @Override
  int hashCode();
}

缓存Key的生成

private final EngineKeyFactory keyFactory;
/**Engine类的load方法*/
public <R> LoadStatus load(GlideContext glideContext,Object model, Key signature,int width,int height,Class<?> resourceClass,Class<R> transcodeClass,Priority priority,DiskCacheStrategy diskCacheStrategy,Map<Class<?>, Transformation<?>> transformations,boolean isTransformationRequired,boolean isScaleOnlyOrNoTransform, Options options,boolean isMemoryCacheable,boolean useUnlimitedSourceExecutorPool,boolean useAnimationPool,boolean onlyRetrieveFromCache,ResourceCallback cb) {
    Util.assertMainThread();
    long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;

    EngineKey key = keyFactory.buildKey(model, signature, width, height, transformations,
        resourceClass, transcodeClass, options);
    //省略部分代码
    ..........
  }
/**EngineKey类*/  
class EngineKey implements Key {
  private final Object model;
  private final int width;
  private final int height;
  private final Class<?> resourceClass;
  private final Class<?> transcodeClass;
  private final Key signature;
  private final Map<Class<?>, Transformation<?>> transformations;
  private final Options options;
  private int hashCode;

  EngineKey(
      Object model,
      Key signature,
      int width,
      int height,
      Map<Class<?>, Transformation<?>> transformations,
      Class<?> resourceClass,
      Class<?> transcodeClass,
      Options options) {
    this.model = Preconditions.checkNotNull(model);
    this.signature = Preconditions.checkNotNull(signature, "Signature must not be null");
    this.width = width;
    this.height = height;
    this.transformations = Preconditions.checkNotNull(transformations);
    this.resourceClass =
        Preconditions.checkNotNull(resourceClass, "Resource class must not be null");
    this.transcodeClass =
        Preconditions.checkNotNull(transcodeClass, "Transcode class must not be null");
    this.options = Preconditions.checkNotNull(options);
  }

  @Override
  public boolean equals(Object o) {
    if (o instanceof EngineKey) {
      EngineKey other = (EngineKey) o;
      return model.equals(other.model)
          && signature.equals(other.signature)
          && height == other.height
          && width == other.width
          && transformations.equals(other.transformations)
          && resourceClass.equals(other.resourceClass)
          && transcodeClass.equals(other.transcodeClass)
          && options.equals(other.options);
    }
    return false;
  }

  @Override
  public int hashCode() {
    if (hashCode == 0) {
      hashCode = model.hashCode();
      hashCode = 31 * hashCode + signature.hashCode();
      hashCode = 31 * hashCode + width;
      hashCode = 31 * hashCode + height;
      hashCode = 31 * hashCode + transformations.hashCode();
      hashCode = 31 * hashCode + resourceClass.hashCode();
      hashCode = 31 * hashCode + transcodeClass.hashCode();
      hashCode = 31 * hashCode + options.hashCode();
    }
    return hashCode;
  }
}

LRU

LRU算法思想

内存缓存

内存缓存相关API

//跳过内存缓存
RequestOptions requestOptions =new RequestOptions().skipMemoryCache(true);
Glide.with(this).load(IMAGE_URL).apply(requestOptions).into(imageView);
//Generated API 方式
GlideApp.with(this).load(IMAGE_URL).skipMemoryCache(true).into(imageView); 
//清除内存缓存，必须在主线程中调用
Glide.get(context).clearMemory();

内存缓存源码分析

/**Engine类的load方法*/
public <R> LoadStatus load(GlideContext glideContext,Object model, Key signature,int width,int height,Class<?> resourceClass,Class<R> transcodeClass,Priority priority,DiskCacheStrategy diskCacheStrategy,Map<Class<?>, Transformation<?>> transformations,boolean isTransformationRequired,boolean isScaleOnlyOrNoTransform, Options options,boolean isMemoryCacheable,boolean useUnlimitedSourceExecutorPool,boolean useAnimationPool,boolean onlyRetrieveFromCache,ResourceCallback cb) {
    //省略部分代码
    ..........
    EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
    if (active != null) {
      cb.onResourceReady(active, DataSource.MEMORY_CACHE);
      if (VERBOSE_IS_LOGGABLE) {
        logWithTimeAndKey("Loaded resource from active resources", startTime, key);
      }
      return null;
    }
    //省略部分代码
    ..........
  }
活动资源 (Active Resources)
private final ActiveResources activeResources;
/**Engine类的loadFromActiveResources方法*/
@Nullable
  private EngineResource<?> loadFromActiveResources(Key key, boolean isMemoryCacheable) {
    if (!isMemoryCacheable) {
      return null;
    }
    EngineResource<?> active = activeResources.get(key);
    if (active != null) {
      active.acquire();
    }
    return active;
  }
/**ActiveResources类*/
final class ActiveResources {
     @VisibleForTesting
  final Map<Key, ResourceWeakReference> activeEngineResources = new HashMap<>();
   //省略部分代码
    ........
   @VisibleForTesting
  static final class ResourceWeakReference extends WeakReference<EngineResource<?>> {
    //省略部分代码
    ........
  }
}
/**Engine类的onEngineJobComplete方法*/
@SuppressWarnings("unchecked")
  @Override
  public void onEngineJobComplete(EngineJob<?> engineJob, Key key, EngineResource<?> resource) {
    Util.assertMainThread();
    // A null resource indicates that the load failed, usually due to an exception.
    if (resource != null) {
      resource.setResourceListener(key, this);

      if (resource.isCacheable()) {
        activeResources.activate(key, resource);
      }
    }

    jobs.removeIfCurrent(key, engineJob);
  }

/**RequestOptions类的skipMemoryCache方法*/
public RequestOptions skipMemoryCache(boolean skip) {
    if (isAutoCloneEnabled) {
      return clone().skipMemoryCache(true);
    }
    this.isCacheable = !skip;
    fields |= IS_CACHEABLE;
    return selfOrThrowIfLocked();
  }
内存缓存 (Memory cache)
/**Engine类的load方法*/
public <R> LoadStatus load(GlideContext glideContext,Object model, Key signature,int width,int height,Class<?> resourceClass,Class<R> transcodeClass,Priority priority,DiskCacheStrategy diskCacheStrategy,Map<Class<?>, Transformation<?>> transformations,boolean isTransformationRequired,boolean isScaleOnlyOrNoTransform, Options options,boolean isMemoryCacheable,boolean useUnlimitedSourceExecutorPool,boolean useAnimationPool,boolean onlyRetrieveFromCache,ResourceCallback cb) {
    //省略部分代码
    ..........
    EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
    if (cached != null) {
      cb.onResourceReady(cached, DataSource.MEMORY_CACHE);
      if (VERBOSE_IS_LOGGABLE) {
        logWithTimeAndKey("Loaded resource from cache", startTime, key);
      }
      return null;
    }
    //省略部分代码
    ..........
  }
/**Engine类的loadFromCache方法*/
private EngineResource<?> loadFromCache(Key key, boolean isMemoryCacheable) {
    if (!isMemoryCacheable) {
      return null;
    }

    EngineResource<?> cached = getEngineResourceFromCache(key);
    if (cached != null) {
      cached.acquire();
      activeResources.activate(key, cached);
    }
    return cached;
  }
/**Engine类的getEngineResourceFromCache方法*/
private final MemoryCache cache;
private EngineResource<?> getEngineResourceFromCache(Key key) {
    Resource<?> cached = cache.remove(key);

    final EngineResource<?> result;
    if (cached == null) {
      result = null;
    } else if (cached instanceof EngineResource) {
      // Save an object allocation if we've cached an EngineResource (the typical case).
      result = (EngineResource<?>) cached;
    } else {
      result = new EngineResource<>(cached, true /*isMemoryCacheable*/, true /*isRecyclable*/);
    }
    return result;
  }
/**GlideBuilder类的build方法*/
private  MemoryCache cache;
@NonNull
  Glide build(@NonNull Context context) {
    //省略部分代码
    ..........
    if (memoryCache == null) {
      memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());
    }

    if (diskCacheFactory == null) {
      diskCacheFactory = new InternalCacheDiskCacheFactory(context);
    }

    if (engine == null) {
      engine =
          new Engine(
              memoryCache,
              diskCacheFactory,
              diskCacheExecutor,
              sourceExecutor,
              GlideExecutor.newUnlimitedSourceExecutor(),
              GlideExecutor.newAnimationExecutor(),
              isActiveResourceRetentionAllowed);
    }
    //省略部分代码
    ..........
}    
/**LruResourceCache类的实现继承关系*/    
public class LruResourceCache extends LruCache<Key, Resource<?>> implements MemoryCache{......}
内存缓存写入
/**EngineJob类的handleResultOnMainThread方法*/
@Synthetic
  void handleResultOnMainThread() {
    //省略部分代码
    ..........
    engineResource = engineResourceFactory.build(resource, isCacheable);
    hasResource = true;
    //省略部分代码
    ..........
    engineResource.acquire();
    listener.onEngineJobComplete(this, key, engineResource);
    engineResource.release();
    //省略部分代码
    ..........
  }
/**EngineJob类的EngineResourceFactory内部类*/  
@VisibleForTesting
  static class EngineResourceFactory {
    public <R> EngineResource<R> build(Resource<R> resource, boolean isMemoryCacheable) {
      return new EngineResource<>(resource, isMemoryCacheable, /*isRecyclable=*/ true);
    }
  }
/**Engine类的onEngineJobComplete方法*/
@SuppressWarnings("unchecked")
  @Override
  public void onEngineJobComplete(EngineJob<?> engineJob, Key key, EngineResource<?> resource) {
    //省略部分代码
    ..........
    if (resource != null) {
      resource.setResourceListener(key, this);
      if (resource.isCacheable()) {
        activeResources.activate(key, resource);
      }
    }
    //省略部分代码
    ..........
  }  

/**EngineResource类的acquire方法*/
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;
  }
/**EngineResource类的release方法*/
  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);
    }
  }
/**Engine类的onResourceReleased方法*/
@Override
  public void onResourceReleased(Key cacheKey, EngineResource<?> resource) {
    Util.assertMainThread();
    activeResources.deactivate(cacheKey);
    if (resource.isCacheable()) {
      cache.put(cacheKey, resource);
    } else {
      resourceRecycler.recycle(resource);
    }
  }
Glide内存缓存机制示意图
Glide内存缓存机制示意图.jpg

磁盘缓存

RequestOptions requestOptions = new RequestOptions()
         .diskCacheStrategy(DiskCacheStrategy.NONE);//不使用缓存
     Glide.with(Context).load(IMAGE_URL).apply(requestOptions).into(mImageView);

磁盘缓存策略

磁盘缓存源码分析

/**DecodeJob类的start方法*/
public void start(DecodeJob<R> decodeJob) {
    this.decodeJob = decodeJob;
    GlideExecutor executor = decodeJob.willDecodeFromCache()
        ? diskCacheExecutor
        : getActiveSourceExecutor();
    executor.execute(decodeJob);
  }
/**DecodeJob类的willDecodeFromCache方法*/ 
 boolean willDecodeFromCache() {
    Stage firstStage = getNextStage(Stage.INITIALIZE);
    return firstStage == Stage.RESOURCE_CACHE || firstStage == Stage.DATA_CACHE;
  } 
/**DecodeJob类的getNextStage方法*/   
private Stage getNextStage(Stage current) {
    switch (current) {
      case INITIALIZE:
        return diskCacheStrategy.decodeCachedResource()
            ? Stage.RESOURCE_CACHE : getNextStage(Stage.RESOURCE_CACHE);
      case RESOURCE_CACHE:
        return diskCacheStrategy.decodeCachedData()
            ? Stage.DATA_CACHE : getNextStage(Stage.DATA_CACHE);
      case DATA_CACHE:
        return onlyRetrieveFromCache ? Stage.FINISHED : Stage.SOURCE;
     //省略部分代码
    ......
    }
  }
/**DiskCacheStrategy类的ALL对象*/     
public static final DiskCacheStrategy ALL = new DiskCacheStrategy() {
    @Override
    public boolean isDataCacheable(DataSource dataSource) {
      return dataSource == DataSource.REMOTE;
    }

    @Override
    public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
        EncodeStrategy encodeStrategy) {
      return dataSource != DataSource.RESOURCE_DISK_CACHE && dataSource != DataSource.MEMORY_CACHE;
    }

    @Override
    public boolean decodeCachedResource() {
      return true;
    }

    @Override
    public boolean decodeCachedData() {
      return true;
    }
  };  
/**GlideBuilder类的build方法*/  
@NonNull
  Glide build(@NonNull Context context) {
    //省略部分代码
    ......
    if (diskCacheExecutor == null) {
      diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
    }
    //省略部分代码
    ......
}
/**GlideExecutor类的newDiskCacheExecutor方法*/ 
private static final int DEFAULT_DISK_CACHE_EXECUTOR_THREADS = 1;
public static GlideExecutor newDiskCacheExecutor() {
    return newDiskCacheExecutor(
        DEFAULT_DISK_CACHE_EXECUTOR_THREADS,
        DEFAULT_DISK_CACHE_EXECUTOR_NAME,
        UncaughtThrowableStrategy.DEFAULT);
  }
/**GlideExecutor类的newDiskCacheExecutor方法*/ 
 public static GlideExecutor newDiskCacheExecutor(
      int threadCount, String name, UncaughtThrowableStrategy uncaughtThrowableStrategy) {
    return new GlideExecutor(
        new ThreadPoolExecutor(
            threadCount /* corePoolSize */,
            threadCount /* maximumPoolSize */,
            0 /* keepAliveTime */,
            TimeUnit.MILLISECONDS,
            new PriorityBlockingQueue<Runnable>(),
            new DefaultThreadFactory(name, uncaughtThrowableStrategy, true)));
  }  

/**GlideBuilder类的build方法*/  
private DiskCache.Factory diskCacheFactory;
@NonNull
  Glide build(@NonNull Context context) {
    //省略部分代码
    ..........
    if (diskCacheFactory == null) {
      diskCacheFactory = new InternalCacheDiskCacheFactory(context);
    }
    //省略部分代码
    ..........
}
/**InternalCacheDiskCacheFactory类的继承关系*/
public final class InternalCacheDiskCacheFactory extends DiskLruCacheFactory {
   //省略实现代码
    ..........  
}
/**DiskLruCacheFactory类的部分代码*/
public class DiskLruCacheFactory implements DiskCache.Factory {
   //省略部分代码
    ..........
    @Override
  public DiskCache build() {
    File cacheDir = cacheDirectoryGetter.getCacheDirectory();
    //省略部分代码
    ..........
    return DiskLruCacheWrapper.create(cacheDir, diskCacheSize);
  }
}
/**DiskLruCacheWrapper类的部分代码*/
public class DiskLruCacheWrapper implements DiskCache {
//省略部分代码
    ..........
   private synchronized DiskLruCache getDiskCache() throws IOException {
    if (diskLruCache == null) {
      diskLruCache = DiskLruCache.open(directory, APP_VERSION, VALUE_COUNT, maxSize);
    }
    return diskLruCache;
  } 
  //省略部分代码
    ..........
}
/**DiskLruCache类的部分代码*/
public final class DiskLruCache implements Closeable {
    //省略部分代码
    ..........
    public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)
      throws IOException {
          DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
          //省略部分代码
          ..........
          return cache;
      }
      //省略部分代码
      ..........
}
资源类型（Resource）
/**DecodeJob的getNextGenerator方法*/
private DataFetcherGenerator getNextGenerator() {
    switch (stage) {
      case RESOURCE_CACHE:
        return new ResourceCacheGenerator(decodeHelper, this);
      case DATA_CACHE:
        return new DataCacheGenerator(decodeHelper, this);
      case SOURCE:
        return new SourceGenerator(decodeHelper, this);
      case FINISHED:
        return null;
      default:
        throw new IllegalStateException("Unrecognized stage: " + stage);
    }
  }

/** ResourceCacheGenerator类的startNext方法*/
  @SuppressWarnings("PMD.CollapsibleIfStatements")
  @Override
  public boolean startNext() {
     //省略部分代码
      ..........
      currentKey =
          new ResourceCacheKey(// NOPMD AvoidInstantiatingObjectsInLoops
              helper.getArrayPool(),
              sourceId,
              helper.getSignature(),
              helper.getWidth(),
              helper.getHeight(),
              transformation,
              resourceClass,
              helper.getOptions());
      cacheFile = helper.getDiskCache().get(currentKey);
      if (cacheFile != null) {
        sourceKey = sourceId;
        modelLoaders = helper.getModelLoaders(cacheFile);
        modelLoaderIndex = 0;
      }
    }

    loadData = null;
    boolean started = false;
    while (!started && hasNextModelLoader()) {
      ModelLoader<File, ?> modelLoader = modelLoaders.get(modelLoaderIndex++);
      loadData = modelLoader.buildLoadData(cacheFile,
          helper.getWidth(), helper.getHeight(), helper.getOptions());
      if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {
        started = true;
        loadData.fetcher.loadData(helper.getPriority(), this);
      }
    }
    return started;
  }
/**DecodeHelper类的getDiskCache方法*/
 DiskCache getDiskCache() {
    return diskCacheProvider.getDiskCache();
  }
/** LazyDiskCacheProvider类的getDiskCache方法 */
@Override
    public DiskCache getDiskCache() {
      if (diskCache == null) {
        synchronized (this) {
          if (diskCache == null) {
            diskCache = factory.build();
          }
          if (diskCache == null) {
            diskCache = new DiskCacheAdapter();
          }
        }
      }
      return diskCache;
    }  

/** ResourceCacheGenerator类的startNext方法*/
 @Override
  public void onDataReady(Object data) {
    cb.onDataFetcherReady(sourceKey, data, loadData.fetcher, DataSource.RESOURCE_DISK_CACHE,
        currentKey);
  }
数据来源 (Data)
/** DataCacheGenerator类的startNext方法*/
 @Override
  public boolean startNext() {
      //省略部分代码
      ..........
      Key originalKey = new DataCacheKey(sourceId, helper.getSignature());
      cacheFile = helper.getDiskCache().get(originalKey);
      if (cacheFile != null) {
        this.sourceKey = sourceId;
        modelLoaders = helper.getModelLoaders(cacheFile);
        modelLoaderIndex = 0;
      }
    }

    loadData = null;
    boolean started = false;
    while (!started && hasNextModelLoader()) {
      ModelLoader<File, ?> modelLoader = modelLoaders.get(modelLoaderIndex++);
      loadData =
          modelLoader.buildLoadData(cacheFile, helper.getWidth(), helper.getHeight(),
              helper.getOptions());
      if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {
        started = true;
        loadData.fetcher.loadData(helper.getPriority(), this);
      }
    }
    return started;
  }
/** DataCacheGenerator类的onDataReady方法*/  
@Override
  public void onDataReady(Object data) {
    cb.onDataFetcherReady(sourceKey, data, loadData.fetcher, DataSource.DATA_DISK_CACHE, sourceKey);
  }
磁盘缓存数据存入
/** DecodeJob类的decodeFromRetrievedData方法*/  
private void decodeFromRetrievedData() {
    //省略部分代码
      ..........
    notifyEncodeAndRelease(resource, currentDataSource);
    //省略部分代码
      ..........
} 
/** DecodeJob类的notifyEncodeAndRelease方法*/  
private final DeferredEncodeManager<?> deferredEncodeManager = new DeferredEncodeManager<>();
private void notifyEncodeAndRelease(Resource<R> resource, DataSource dataSource) {
//省略部分代码
      ..........
    stage = Stage.ENCODE;
    try {
      if (deferredEncodeManager.hasResourceToEncode()) {
        deferredEncodeManager.encode(diskCacheProvider, options);
      }
    } 
    //省略部分代码
    ..........
  }
/** DeferredEncodeManager类的encode方法**/
void encode(DiskCacheProvider diskCacheProvider, Options options) {
      GlideTrace.beginSection("DecodeJob.encode");
      try {
        diskCacheProvider.getDiskCache().put(key,
            new DataCacheWriter<>(encoder, toEncode, options));
      } finally {
        toEncode.unlock();
        GlideTrace.endSection();
      }
    } 

/**SourceGenerator类的onDataReady方法**/ 
private Object dataToCache;
@Override
  public void onDataReady(Object data) {
    DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy();
    if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) {
      dataToCache = data;
      cb.reschedule();
    } else {
      cb.onDataFetcherReady(loadData.sourceKey, data, loadData.fetcher,
          loadData.fetcher.getDataSource(), originalKey);
    }
  }  
/**SourceGenerator类的startNext方法**/
@Override
  public boolean startNext() {
    if (dataToCache != null) {
      Object data = dataToCache;
      dataToCache = null;
      cacheData(data);
    }

    if (sourceCacheGenerator != null && sourceCacheGenerator.startNext()) {
      return true;
    }
   //省略部分代码
  ..........
  }
/**SourceGenerator类的cacheData方法**/  
private void cacheData(Object dataToCache) {
    long startTime = LogTime.getLogTime();
    try {
      Encoder<Object> encoder = helper.getSourceEncoder(dataToCache);
      DataCacheWriter<Object> writer =
          new DataCacheWriter<>(encoder, dataToCache, helper.getOptions());
      originalKey = new DataCacheKey(loadData.sourceKey, helper.getSignature());
      helper.getDiskCache().put(originalKey, writer);
    } 
    //省略部分代码
    ..........
    sourceCacheGenerator =
        new DataCacheGenerator(Collections.singletonList(loadData.sourceKey), helper, this);
  }
/**DecodeJob类的reschedule方法**/ 
@Override
  public void reschedule() {
    runReason = RunReason.SWITCH_TO_SOURCE_SERVICE;
    callback.reschedule(this);
  }
/**Engine类的reschedule方法**/   
 @Override
  public void reschedule(DecodeJob<?> job) {
    getActiveSourceExecutor().execute(job);
  }

仅从缓存加载图片

RequestOptions requestOptions = new RequestOptions().onlyRetrieveFromCache(true);
Glide.with(this).load(IMAGE_URL).apply(requestOptions).into(mImageView);
//Generated API 方式        
GlideApp.with(this)
  .load(url)
  .diskCacheStrategy(DiskCacheStrategy.ALL)
  .into(mImageView);        

/**DecodeJob类的getNextStage方法**/ 
private Stage getNextStage(Stage current) {
    switch (current) {
    //省略部分代码
    ..........
      case DATA_CACHE:
        return onlyRetrieveFromCache ? Stage.FINISHED : Stage.SOURCE;
      case SOURCE:
      case FINISHED:
        return Stage.FINISHED;
    }
  }
/**DecodeJob类的getNextGenerator方法**/   
private DataFetcherGenerator getNextGenerator() {
    switch (stage) {
    //省略部分代码
    ..........
      case FINISHED:
        return null;
      default:
        throw new IllegalStateException("Unrecognized stage: " + stage);
    }
  }
Glide磁盘缓存机制示意图
Glide磁盘缓存机制示意图.jpg

Glide缓存小结

Glide 回调与监听

图片加载成功回调原理

/**SingleRequest类的onResourceReady方法**/    
@Nullable 
private List<RequestListener<R>> requestListeners;
private void onResourceReady(Resource<R> resource, R result, DataSource dataSource) {
    //省略部分代码
    ..........
    isCallingCallbacks = true;
    try {
      boolean anyListenerHandledUpdatingTarget = false;
      //省略部分代码
     ..........

      if (!anyListenerHandledUpdatingTarget) {
        Transition<? super R> animation =
            animationFactory.build(dataSource, isFirstResource);
        target.onResourceReady(result, animation);
      }
    } 
    //省略部分代码
    ..........
  }
/**Target 接口**/      
public interface Target<R> extends LifecycleListener {}
/**ImageViewTarget类的onResourceReady方法**/ 
@Override
  public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
    if (transition == null || !transition.transition(resource, this)) {
      setResourceInternal(resource);
    } else {
      maybeUpdateAnimatable(resource);
    }
  }
/**ImageViewTarget类的setResourceInternal方法**/ 
private void setResourceInternal(@Nullable Z resource) {
    setResource(resource);
    maybeUpdateAnimatable(resource);
  }
DrawableImageViewTarget
/**DrawableImageViewTarget类的setResource方法**/ 
 @Override
  protected void setResource(@Nullable Drawable resource) {
    view.setImageDrawable(resource);
  }

Glide监听（listener）

Glide.with(this).load(IMAGE_URL).listener(new RequestListener<Drawable>() {
           @Override
           public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable> target, boolean isFirstResource) {
               return false;
           }

           @Override
           public boolean onResourceReady(Drawable resource, Object model, Target<Drawable> target, DataSource dataSource, boolean isFirstResource) {
               return false;
           }
       }).into(mImageView);

/**RequestBuilder类的listener方法**/ 
@Nullable 
private List<RequestListener<TranscodeType>> requestListeners;
  public RequestBuilder<TranscodeType> listener(
      @Nullable RequestListener<TranscodeType> requestListener) {
    this.requestListeners = null;
    return addListener(requestListener);
  }
/**RequestBuilder类的addListener方法**/  
  public RequestBuilder<TranscodeType> addListener(
      @Nullable RequestListener<TranscodeType> requestListener) {
    if (requestListener != null) {
      if (this.requestListeners == null) {
        this.requestListeners = new ArrayList<>();
      }
      this.requestListeners.add(requestListener);
    }
    return this;
  }

/**SingleRequest类的onResourceReady方法**/    
@Nullable 
private List<RequestListener<R>> requestListeners;
private void onResourceReady(Resource<R> resource, R result, DataSource dataSource) {
    //省略部分代码
    ..........
    isCallingCallbacks = true;
    try {
      boolean anyListenerHandledUpdatingTarget = false;
      if (requestListeners != null) {
        for (RequestListener<R> listener : requestListeners) {
          anyListenerHandledUpdatingTarget |=
              listener.onResourceReady(result, model, target, dataSource, isFirstResource);
        }
      }
      anyListenerHandledUpdatingTarget |=
          targetListener != null
              && targetListener.onResourceReady(result, model, target, dataSource, isFirstResource);

      if (!anyListenerHandledUpdatingTarget) {
        Transition<? super R> animation =
            animationFactory.build(dataSource, isFirstResource);
        target.onResourceReady(result, animation);
      }
    } 
    //省略部分代码
    ..........
  }

Target（目标）

简单的Target（SimpleTarget）

//注意需要指定Glide的加载类型asBitmap，不指定Target不知道本身是是类型的Target
Glide.with(this).asBitmap().load(IMAGE_URL).into(new SimpleTarget<Bitmap>() {
            @Override
            public void onResourceReady(@NonNull Bitmap resource, @Nullable Transition<? super Bitmap> transition) {
            //加载完成已经在主线程
                mImageView.setImageBitmap(resource);
            }
        });

特定View的Target(ViewTarget)

/**
 * @author maoqitian
 * @Description: 自定义RelativeLayout
 * @date 2019/2/18 0018 19:51
 */

public class MyView extends RelativeLayout {
    private ViewTarget<MyView, Drawable> viewTarget;
    public MyView(Context context) {
        super(context);
    }

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        viewTarget =new ViewTarget<MyView, Drawable>(this) {
            @Override
            public void onResourceReady(@NonNull Drawable resource, @Nullable Transition<? super Drawable> transition) {
                setBackground(resource);
            }
        };
    }

    public ViewTarget<MyView, Drawable> getViewTarget() {
        return viewTarget;
    }
}

//使用Glide加载
MyView rl_view = findViewById(R.id.rl_view);
Glide.with(this).load(IMAGE_URL).into(rl_view.getViewTarget());

FutureTarget

new Thread(new Runnable() {
            @Override
            public void run() {
                FutureTarget<File> target = null;
                RequestManager requestManager = Glide.with(MainActivity.this);
                try {
                    target = requestManager
                            .downloadOnly()
                            .load(IMAGE_URL)
                            .submit();
                    final File downloadedFile = target.get();
                    Log.i(TAG,"缓存文件路径"+downloadedFile.getAbsolutePath());
                } catch (ExecutionException | InterruptedException e) {

                } finally {
                    if (target != null) {
                        target.cancel(true); // mayInterruptIfRunning
                    }
                }
            }
        }).start();

preload（预加载）

Glide.with(this).load(IMAGE_URL).preload();

/**RequestBuilder类的preload方法**/
 @NonNull
  public Target<TranscodeType> preload() {
    return preload(Target.SIZE_ORIGINAL, Target.SIZE_ORIGINAL);
  }
/**RequestBuilder类的preload方法**/ 
@NonNull
  public Target<TranscodeType> preload(int width, int height) {
    final PreloadTarget<TranscodeType> target = PreloadTarget.obtain(requestManager, width, height);
    return into(target);
  }
/**RequestBuilder类的onResourceReady方法**/   
public final class PreloadTarget<Z> extends SimpleTarget<Z> {

private static final Handler HANDLER = new Handler(Looper.getMainLooper(), new Callback() {
    @Override
    public boolean handleMessage(Message message) {
      if (message.what == MESSAGE_CLEAR) {
        ((PreloadTarget<?>) message.obj).clear();
        return true;
      }
      return false;
    }
  });

//省略部分代码
    ..........
public static <Z> PreloadTarget<Z> obtain(RequestManager requestManager, int width, int height) {
    return new PreloadTarget<>(requestManager, width, height);
  } 

@Override
  public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
    HANDLER.obtainMessage(MESSAGE_CLEAR, this).sendToTarget();
  }
  //省略部分代码
    ..........
}

Generated API

//在app下的gradle添加Glide注解处理器的依赖
dependencies {
  annotationProcessor 'com.github.bumptech.glide:compiler:4.8.0'
}
//新建一个类集成AppGlideModule并添加上@GlideModule注解，重新rebuild项目就可以使用GlideApp了
@GlideModule
public final class MyAppGlideModule extends AppGlideModule {}


/**GlideApp类部分代码**/ 
public final class GlideApp {
    //省略部分代码
    ..........
    @NonNull
    public static GlideRequests with(@NonNull Context context) {
    return (GlideRequests) Glide.with(context);
  }
  //省略部分代码
    ..........
}
/**GlideApp类部分代码**/ 
public class GlideRequest<TranscodeType> extends RequestBuilder<TranscodeType> implements Cloneable {
//省略部分代码
    ..........
  @NonNull
  @CheckResult
  public GlideRequest<TranscodeType> placeholder(@Nullable Drawable drawable) {
    if (getMutableOptions() instanceof GlideOptions) {
      this.requestOptions = ((GlideOptions) getMutableOptions()).placeholder(drawable);
    } else {
      this.requestOptions = new GlideOptions().apply(this.requestOptions).placeholder(drawable);
    }
    return this;
  }
  //省略部分代码
    ..........
}
/**RequestBuilder类的getMutableOptions方法**/ 
protected RequestOptions getMutableOptions() {
    return defaultRequestOptions == this.requestOptions
        ? this.requestOptions.clone() : this.requestOptions;
  }

GlideExtension

@GlideOption

/**
 * @author maoqitian
 * @Description: GlideApp 功能扩展类
 * @date 2019/2/19 0019 12:51
 */
@GlideExtension
public class MyGlideExtension {

    private MyGlideExtension() {
    }

    //可以为方法任意添加参数，但要保证第一个参数为 RequestOptions
    /**
     * 设置通用的加载占位图和错误加载图
     * @param options
     */
    @GlideOption
    public static void normalPlaceholder(RequestOptions options) {
        options.placeholder(R.drawable.ic_cloud_download_black_24dp).error(R.drawable.ic_error_black_24dp);
    }
}
/**GlideOptions类中生成对应的方法**/
/**
   * @see MyGlideExtension#normalPlaceholder(RequestOptions)
   */
  @CheckResult
  @NonNull
  public GlideOptions normalPlaceholder() {
    if (isAutoCloneEnabled()) {
      return clone().normalPlaceholder();
    }
    MyGlideExtension.normalPlaceholder(this);
    return this;
  }
/**GlideRequest类中生成对应的方法**/  
/**
   * @see GlideOptions#normalPlaceholder()
   */
  @CheckResult
  @NonNull
  public GlideRequest<TranscodeType> normalPlaceholder() {
    if (getMutableOptions() instanceof GlideOptions) {
      this.requestOptions = ((GlideOptions) getMutableOptions()).normalPlaceholder();
    } else {
      this.requestOptions = new GlideOptions().apply(this.requestOptions).normalPlaceholder();
    }
    return this;
  }

//调用我们刚刚设置的扩展功能方法
GlideApp.with(this).load(IMAGE_URL)
                .normalPlaceholder()
                .into(mImageView);

GlideType

@GlideExtension
public class MyGlideExtension {

    private static final RequestOptions DECODE_TYPE_GIF = decodeTypeOf(GifDrawable.class).lock();

    @GlideType(GifDrawable.class)
    public static void asMyGif(RequestBuilder<GifDrawable> requestBuilder) {
        requestBuilder
                .transition(new DrawableTransitionOptions())
                .apply(DECODE_TYPE_GIF);
    }
}

/**GlideRequests类中生成的asMyGif方法**/

/**
   * @see MyGlideExtension#asMyGif(RequestBuilder)
   */
  @NonNull
  @CheckResult
  public GlideRequest<GifDrawable> asMyGif() {
    GlideRequest<GifDrawable> requestBuilder = this.as(GifDrawable.class);
    MyGlideExtension.asMyGif(requestBuilder);
    return requestBuilder;
  }

 GlideApp.with(this).asMyGif().load(IMAGE_URL)
                .into(mImageView);

源码阅读方法思路

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