GenericLoaderFactory

這個類是個靜態工廠

使用這個2個容器 , 把 register 工廠和 build modelLoader 給緩存起來 ;

 private final Map<Class/*T*/, Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/>> modelClassToResourceFactories =
            new HashMap<Class, Map<Class, ModelLoaderFactory>>();

    private final Map<Class/*T*/, Map<Class/*Y*/, ModelLoader/*T, Y*/>> cachedModelLoaders =
            new HashMap<Class, Map<Class, ModelLoader>>();

    public synchronized <T, Y> ModelLoaderFactory<T, Y> register(Class<T> modelClass, Class<Y> resourceClass,
            ModelLoaderFactory<T, Y> factory) {
        cachedModelLoaders.clear();

        Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> resourceToFactories = modelClassToResourceFactories.get(modelClass);
        if (resourceToFactories == null) {
            resourceToFactories = new HashMap<Class/*Y*/, ModelLoaderFactory/*T, Y*/>();
            modelClassToResourceFactories.put(modelClass, resourceToFactories);
        }

        ModelLoaderFactory/*T, Y*/ previous = resourceToFactories.put(resourceClass, factory);

        if (previous != null) {
            // This factory may be being used by another model. We don't want to say it has been removed unless we
            // know it has been removed for all models.
            for (Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> factories : modelClassToResourceFactories.values()) {
                if (factories.containsValue(previous)) {
                    previous = null;
                    break;
                }
            }
        }

        return previous;
    }


public synchronized <T, Y> ModelLoader<T, Y> buildModelLoader(Class<T> modelClass, Class<Y> resourceClass) {
        ModelLoader<T, Y> result = getCachedLoader(modelClass, resourceClass);
        if (result != null) {
            // We've already tried to create a model loader and can't with the currently registered set of factories,
            // but we can't use null to demonstrate that failure because model loaders that haven't been requested
            // yet will be null in the cache. To avoid this, we use a special signal model loader.
            if (NULL_MODEL_LOADER.equals(result)) {
                return null;
            } else {
                return result;
            }
        }

        final ModelLoaderFactory<T, Y> factory = getFactory(modelClass, resourceClass);
        if (factory != null) {
            result = factory.build(context, this);
            cacheModelLoader(modelClass, resourceClass, result);
        } else {
            // We can't generate a model loader for the given arguments with the currently registered set of factories.
            cacheNullLoader(modelClass, resourceClass);
        }
        return result;
    }

在glide的構造方法里 把需要的參數存起來了

        register(File.class, ParcelFileDescriptor.class, new FileDescriptorFileLoader.Factory());
        register(File.class, InputStream.class, new StreamFileLoader.Factory());
        register(int.class, ParcelFileDescriptor.class, new FileDescriptorResourceLoader.Factory());
        register(int.class, InputStream.class, new StreamResourceLoader.Factory());
        register(Integer.class, ParcelFileDescriptor.class, new FileDescriptorResourceLoader.Factory());
        register(Integer.class, InputStream.class, new StreamResourceLoader.Factory());
        register(String.class, ParcelFileDescriptor.class, new FileDescriptorStringLoader.Factory());
        register(String.class, InputStream.class, new StreamStringLoader.Factory());
        register(Uri.class, ParcelFileDescriptor.class, new FileDescriptorUriLoader.Factory());
        register(Uri.class, InputStream.class, new StreamUriLoader.Factory());
        register(URL.class, InputStream.class, new StreamUrlLoader.Factory());
        register(GlideUrl.class, InputStream.class, new HttpUrlGlideUrlLoader.Factory());
        register(byte[].class, InputStream.class, new StreamByteArrayLoader.Factory());

這個register 方法會吧數據給存到GenericLoaderFactory類里

   public <T, Y> void register(Class<T> modelClass, Class<Y> resourceClass, ModelLoaderFactory<T, Y> factory) {
        ModelLoaderFactory<T, Y> removed = loaderFactory.register(modelClass, resourceClass, factory);
        if (removed != null) {
            removed.teardown();
        }
    }

默認是按照這個接口默認進行解耦的

/**
 *
 * @param <T>  GlideUrl.class
 * @param <Y>  InputStream.class
 * @param ModelLoader HttpUrlGlideUrlLoader
 * @param DataFetcher HttpUrlFetcher
 */
public interface ModelLoaderFactory<T, Y> {

  ModelLoad<T, Y> build();

  interface ModelLoad<T, Y> {
    DataFetcher<Y> getResourceFetcher(T model);
  }

  interface DataFetcher<T> {
    T loadData();
  }
}

我們來看下 HttpUrlGlideUrlLoader 這個類 , 在glide構造方法里,register時 , 調用了HttpUrlGlideUrlLoader.Factory()

public class HttpUrlGlideUrlLoader implements ModelLoader<GlideUrl, InputStream> {

    private final ModelCache<GlideUrl, GlideUrl> modelCache;

    /**
     * The default factory for {@link com.bumptech.glide.load.model.stream.HttpUrlGlideUrlLoader}s.
     */
    public static class Factory implements ModelLoaderFactory<GlideUrl, InputStream> {
        private final ModelCache<GlideUrl, GlideUrl> modelCache = new ModelCache<GlideUrl, GlideUrl>(500);

        @Override
        public ModelLoader<GlideUrl, InputStream> build(Context context, GenericLoaderFactory factories) {
            return new HttpUrlGlideUrlLoader(modelCache);
        }

        @Override
        public void teardown() {
            // Do nothing.
        }
    }

    public HttpUrlGlideUrlLoader() {
        this(null);
    }

    public HttpUrlGlideUrlLoader(ModelCache<GlideUrl, GlideUrl> modelCache) {
        this.modelCache = modelCache;
    }

    @Override
    public DataFetcher<InputStream> getResourceFetcher(GlideUrl model, int width, int height) {
        // GlideUrls memoize parsed URLs so caching them saves a few object instantiations and time spent parsing urls.
        GlideUrl url = model;
        if (modelCache != null) {
            url = modelCache.get(model, 0, 0);
            if (url == null) {
                modelCache.put(model, 0, 0, model);
                url = model;
            }
        }
        return new HttpUrlFetcher(url);
    }
}