前言
由名字可以看出这是一个解码的帮助类，里面缓存了LoadData和Key，以及很多从DecoderJob传递过来的参数。它的主要作用是提供解码所需要的的数据，并不进行实际的解码操作。
final class DecodeHelper {
private final List> loadData = new ArrayList<>();
private final List cacheKeys = new ArrayList<>();
private Map, Transformation> transformations; //在BaseRequestOptions中为CachedHashCodeArrayMap
private Object model; //String
private Class resourceClass; //Object.class
private Class transcodeClass; //Drawable.class
}
getCacheKeys()
在这里获取缓存到的key，如果没有则会先获取LoadData，再获取LoadData里面的key。在Glide源码解析之RequestBuilder我们在load()传入的为String类型的 url,所以我们的model为String，则最终cacheKeys会包含GlideUrl（实现了Key接口），在下面会进行分析。
List getCacheKeys() {
if (!isCacheKeysSet) {
isCacheKeysSet = true;
cacheKeys.clear();
List> loadData = getLoadData();
//将LoadData里面的key都缓存起来
for (int i = 0, size = loadData.size(); i < size; i++) {
LoadData data = loadData.get(i);
if (!cacheKeys.contains(data.sourceKey)) {
cacheKeys.add(data.sourceKey);
}
for (int j = 0; j < data.alternateKeys.size(); j++) {
if (!cacheKeys.contains(data.alternateKeys.get(j))) {
cacheKeys.add(data.alternateKeys.get(j));
}
}
}
}
return cacheKeys;
}
getLoadData()
LoadData是一个封装了Key、List
class LoadData {
public final Key sourceKey;
public final List alternateKeys; //默认会赋值为Collections.emptyList()
public final DataFetcher fetcher;
}
List> getLoadData() {
if (!isLoadDataSet) {
isLoadDataSet = true;
loadData.clear();
List> modelLoaders = glideContext.getRegistry().getModelLoaders(model);
for (int i = 0, size = modelLoaders.size(); i < size; i++) {
ModelLoader modelLoader = modelLoaders.get(i);
LoadData current =
modelLoader.buildLoadData(model, width, height, options);
if (current != null) {
loadData.add(current);
}
}
}
return loadData;
}
getModelLoaders()
获取能处理当前类型的ModelLoaders，而ModelLoader实际是由MultiModelLoaderFactory去build出来的。在MultiModelLoaderFactory中，将ModelLoaderFactory、modelClass(要加载的model，这里是String.class)、dataClass(加载的数据类型，例如InputStream.class)包装成一个Entry，就像上面的LoadData那样。而Entry的来源则是在Glide初始化的时候，由Registry设置给ModelLoaderRegistry，再设置给MultiModelLoaderFactory。
//Registry
public List> getModelLoaders(@NonNull Model model) {
List> result = modelLoaderRegistry.getModelLoaders(model);
if (result.isEmpty()) {
throw new NoModelLoaderAvailableException(model);
}
return result;
}
//ModelLoaderRegistry
public List> getModelLoaders(@NonNull A model) {
List> modelLoaders = getModelLoadersForClass(getClass(model));
int size = modelLoaders.size();
boolean isEmpty = true;
List> filteredLoaders = Collections.emptyList();
for (int i = 0; i < size; i++) {
ModelLoader loader = modelLoaders.get(i);
if (loader.handles(model)) { //是否能处理model类型
if (isEmpty) {
filteredLoaders = new ArrayList<>(size - i);
isEmpty = false;
}
filteredLoaders.add(loader);
}
}
return filteredLoaders;
}
//首先从缓存获取，获取不到再build一个新的，并存入缓存
private synchronized List> getModelLoadersForClass(
@NonNull Class modelClass) {
List> loaders = cache.get(modelClass);
if (loaders == null) {
loaders = Collections.unmodifiableList(multiModelLoaderFactory.build(modelClass));
cache.put(modelClass, loaders);
}
return loaders;
}
public class MultiModelLoaderFactory {
private final List> entries = new ArrayList<>();
private static class Entry {
private final Class modelClass;
@Synthetic
final Class dataClass;
@Synthetic
final ModelLoaderFactory factory;
public Entry(
@NonNull Class modelClass,
@NonNull Class dataClass,
@NonNull ModelLoaderFactory factory) {
this.modelClass = modelClass;
this.dataClass = dataClass;
this.factory = factory;
}
public boolean handles(@NonNull Class modelClass) {
return this.modelClass.isAssignableFrom(modelClass); //this.modelClass是否是modelClass的父类或者接口
}
}
synchronized List> build(@NonNull Class modelClass) {
try {
List> loaders = new ArrayList<>();
for (Entry entry : entries) {
if (alreadyUsedEntries.contains(entry)) {
continue;
}
if (entry.handles(modelClass)) {
//由于modelClass是String.class，所以最终只有modelClass为String.class的Entry才能执行到这里。
//比如有Entry(String.class, InputStream.class, new StringLoader.StreamFactory())
//所以loaders会add一个由StreamFactory去build出来的StringLoader。
alreadyUsedEntries.add(entry);
loaders.add(this.build(entry));
alreadyUsedEntries.remove(entry);
}
}
return loaders;
} catch (Throwable t) {
alreadyUsedEntries.clear();
throw t;
}
}
private ModelLoader build(@NonNull Entry entry) {
return (ModelLoader) Preconditions.checkNotNull(entry.factory.build(this));
}
//Entry的来源
private void add(
@NonNull Class modelClass,
@NonNull Class dataClass,
@NonNull ModelLoaderFactory factory,
boolean append) {
Entry entry = new Entry<>(modelClass, dataClass, factory);
entries.add(append ? entries.size() : 0, entry);
}
synchronized void append(
@NonNull Class modelClass,
@NonNull Class dataClass,
@NonNull ModelLoaderFactory factory) {
add(modelClass, dataClass, factory, /*append=*/ true);
}
}
//ModelLoaderRegistry
public synchronized void append(
@NonNull Class modelClass,
@NonNull Class dataClass,
@NonNull ModelLoaderFactory factory) {
multiModelLoaderFactory.append(modelClass, dataClass, factory);
cache.clear();
}
//Registry
public Registry append(
@NonNull Class modelClass, @NonNull Class dataClass,
@NonNull ModelLoaderFactory factory) {
modelLoaderRegistry.append(modelClass, dataClass, factory);
return this;
}
//Glide
Glide(){
registry
.append(String.class, InputStream.class, new DataUrlLoader.StreamFactory())
.append(Uri.class, InputStream.class, new HttpUriLoader.Factory())
.append(String.class, InputStream.class, new StringLoader.StreamFactory())
.append(String.class, ParcelFileDescriptor.class, new StringLoader.FileDescriptorFactory())
.append(GlideUrl.class, InputStream.class, new HttpGlideUrlLoader.Factory())
}
上面说到会由StreamFactory去build一个StringLoader，而StringLoader的构造函数又传入了一个由MultiModelLoaderFactory去build出来的ModelLoader。由于传给它的是Uri.class和InputStream.class，我们去Glide的构造函数找到对应的factory为HttpUriLoader的内部类Factory。它build了一个HttpUriLoader，但同时它的构造函数又传入一个新的ModelLoader，根据类型不难找到实际为HttpGlideUrlLoader。
public static class StreamFactory implements ModelLoaderFactory {
@NonNull
@Override
public ModelLoader build(
@NonNull MultiModelLoaderFactory multiFactory) {
return new StringLoader<>(multiFactory.build(Uri.class, InputStream.class));
}
}
//MultiModelLoaderFactory
public synchronized ModelLoader build(@NonNull Class modelClass,
@NonNull Class dataClass) {
try {
List> loaders = new ArrayList<>();
boolean ignoredAnyEntries = false;
for (Entry entry : entries) {
if (alreadyUsedEntries.contains(entry)) {
ignoredAnyEntries = true;
continue;
}
if (entry.handles(modelClass, dataClass)) {
//匹配Uri.class和InputStream.class的Entry(Uri.class, InputStream.class, new HttpUriLoader.Factory())
alreadyUsedEntries.add(entry);
loaders.add(this.build(entry));
alreadyUsedEntries.remove(entry);
}
}
if (loaders.size() > 1) {
return factory.build(loaders, throwableListPool);
} else if (loaders.size() == 1) {
return loaders.get(0);
} else {
if (ignoredAnyEntries) {
return emptyModelLoader();
} else {
throw new NoModelLoaderAvailableException(modelClass, dataClass);
}
}
} catch (Throwable t) {
alreadyUsedEntries.clear();
throw t;
}
}
//HttpUriLoader
public static class Factory implements ModelLoaderFactory {
@NonNull
@Override
public ModelLoader build(MultiModelLoaderFactory multiFactory) {
return new HttpUriLoader(multiFactory.build(GlideUrl.class, InputStream.class));
}
}
//HttpGlideUrlLoader
public static class Factory implements ModelLoaderFactory {
private final ModelCache modelCache = new ModelCache<>(500);
@NonNull
@Override
public ModelLoader build(MultiModelLoaderFactory multiFactory) {
return new HttpGlideUrlLoader(modelCache);
}
}
StringLoader
StringLoader实现了ModelLoader接口，里面主要是两个方法，handles()在上面ModelLoaderRegistry.getModelLoaders()进行了判断，这里主要看下看下buildLoadData()。
由上面分析可知StringLoader传入了HttpUriLoader，而HttpUriLoader又传入了HttpGlideUrlLoader，所以这里实际上是使用了代理模式，将实际生成LoadData的操作最终交给了HttpGlideUrlLoader。所以最终生成的LoadData的sourceKey为GlideUrl，fetcher为HttpUrlFetcher。
public class StringLoader implements ModelLoader {
private final ModelLoader uriLoader;
public StringLoader(ModelLoader uriLoader) {
this.uriLoader = uriLoader;
}
@Override
public LoadData buildLoadData(@NonNull String model, int width, int height,
@NonNull Options options) {
Uri uri = parseUri(model);
if (uri == null || !uriLoader.handles(uri)) {
return null;
}
return uriLoader.buildLoadData(uri, width, height, options);
}
//是否能处理String类型的model
@Override
public boolean handles(@NonNull String model) {
return true;
}
}
//HttpUriLoader
public LoadData buildLoadData(@NonNull Uri model, int width, int height,
@NonNull Options options) {
//urlLoader为HttpGlideUrlLoader
return urlLoader.buildLoadData(new GlideUrl(model.toString()), width, height, options);
}
//HttpGlideUrlLoader
public LoadData buildLoadData(@NonNull GlideUrl model, int width, int height,
@NonNull Options options) {
GlideUrl url = model;
if (modelCache != null) {
url = modelCache.get(model, 0, 0);
if (url == null) {
modelCache.put(model, 0, 0, model);
url = model;
}
}
int timeout = options.get(TIMEOUT);
return new LoadData<>(url, new HttpUrlFetcher(url, timeout));
}
getRegisteredResourceClasses()
上面说过model.getClass()为String.class，在RequestBuilder的父类BaseRequestOptions中resourceClass默认为Object.class，在Glide源码解析之RequestBuilder我们在load()传入的为String Url,里面会调用asDrawable()，所以这里transcodeClass为Drawable.class。
首先会先从缓存中获取，如果没有则调用modelLoaderRegistry.getDataClasses(modelClass)获取String.class对应的dataClass，然后遍历它，再调用decoderRegistry.getResourceClasses(dataClass, resourceClass)获取对应已注册的resourceClass，最后也遍历registeredResourceClasses，根据registeredResourceClass,和transcodeClass获取最终能处理的registeredResourceClass。所以最后的List会包含Drawable.class。
List> getRegisteredResourceClasses() {
return glideContext.getRegistry()
.getRegisteredResourceClasses(model.getClass(), resourceClass, transcodeClass);
}
//Registry
public List> getRegisteredResourceClasses(
@NonNull Class modelClass /*String*/,
@NonNull Class resourceClass /*Object*/,
@NonNull Class transcodeClass /*Drawable*/) {
List> result =
modelToResourceClassCache.get(modelClass, resourceClass, transcodeClass);
if (result == null) {
result = new ArrayList<>();
List> dataClasses = modelLoaderRegistry.getDataClasses(modelClass); //InputStream.class、ParcelFileDescriptor.class和AssetFileDescriptor.class
for (Class dataClass : dataClasses) {
List> registeredResourceClasses =
decoderRegistry.getResourceClasses(dataClass, resourceClass); //GifDrawable.class、Bitmap.class、BitmapDrawable.class
for (Class registeredResourceClass : registeredResourceClasses) {
List> registeredTranscodeClasses = transcoderRegistry
.getTranscodeClasses(registeredResourceClass, transcodeClass); //Drawable.class
if (!registeredTranscodeClasses.isEmpty() && !result.contains(registeredResourceClass)) {
result.add(registeredResourceClass); //Drawable.class
}
}
}
modelToResourceClassCache.put(
modelClass, resourceClass, transcodeClass, Collections.unmodifiableList(result));
}
return result;
}
getDataClasses()
还是和上面获取ModelLoader一样，这里也是根据Entry中是否能handles()对应的modelClass来获取dataClasses。
由于modelClass为String.class，所以最终返回的List会包含InputStream.class、ParcelFileDescriptor.class和AssetFileDescriptor.class。
//ModelLoaderRegistry
public synchronized List> getDataClasses(@NonNull Class modelClass) {
return multiModelLoaderFactory.getDataClasses(modelClass);
}
//MultiModelLoaderFactory
synchronized List> getDataClasses(@NonNull Class modelClass) {
List> result = new ArrayList<>();
for (Entry entry : entries) {
//上面说了Entry实际会在Glide的构造函数通过Registry的append()赋值，那么只要找出哪些modelClass为String.class对应的dataClass就行了。
if (!result.contains(entry.dataClass) && entry.handles(modelClass)) {
result.add(entry.dataClass);
}
}
return result;
}
Glide(){
registry
.append(String.class, InputStream.class, new DataUrlLoader.StreamFactory())
.append(String.class, InputStream.class, new StringLoader.StreamFactory())
.append(String.class, ParcelFileDescriptor.class, new StringLoader.FileDescriptorFactory())
.append(
String.class, AssetFileDescriptor.class, new StringLoader.AssetFileDescriptorFactory())
}
getResourceClasses()
第一个参数为InputStream.class，第二个参数为Drawable.class。由于decoders保存了所有在Glide构造函数中注册的bucket，所以在Glide的构造函数中找出对应dataClass为InputStream的resource即可。最终这里返回的List会包含GifDrawable.class、Bitmap.class、BitmapDrawable.class。
//ResouceDecoderRegistry
public synchronized List> getResourceClasses(@NonNull Class dataClass,
@NonNull Class resourceClass) {
List> result = new ArrayList<>();
for (String bucket : bucketPriorityList) {
List> entries = decoders.get(bucket);
if (entries == null) {
continue;
}
for (Entry entry : entries) {
if (entry.handles(dataClass, resourceClass)
&& !result.contains(entry.resourceClass)) {
result.add((Class) entry.resourceClass);
}
}
}
return result;
}
ResourceDecoderRegistry
资源解码注册表，和MultiModelLoaderFactory作用类似，它们里面都有一个Entry保存了几个变量，并且都有handles()用来判断这个Entry能否处理对应的类型。
ResourceDecoderRegistry里面有一个bucketPriorityList，它是在Registry在的构造函数里赋值的。同时还用Map来保存了Entry，它则是在Glide的构造函数里通过Registry赋值的。
public class ResourceDecoderRegistry {
private final List bucketPriorityList = new ArrayList<>();
private final Map>> decoders = new HashMap<>();
public synchronized void setBucketPriorityList(@NonNull List buckets) {
List previousBuckets = new ArrayList<>(bucketPriorityList);
bucketPriorityList.clear();
bucketPriorityList.addAll(buckets);
//如果之前bucketPriorityList有的元素是现在没有，则同样保存下来
for (String previousBucket : previousBuckets) {
if (!buckets.contains(previousBucket)) {
bucketPriorityList.add(previousBucket);
}
}
}
private static class Entry {
private final Class dataClass;
@Synthetic
final Class resourceClass;
@Synthetic
final ResourceDecoder decoder;
public Entry(@NonNull Class dataClass, @NonNull Class resourceClass,
ResourceDecoder decoder) {
this.dataClass = dataClass;
this.resourceClass = resourceClass;
this.decoder = decoder;
}
//由于resourceClass默认为Object.class，所以第二个判断为true，只需要判断dataClass就行了
public boolean handles(@NonNull Class dataClass, @NonNull Class resourceClass) {
return this.dataClass.isAssignableFrom(dataClass) && resourceClass
.isAssignableFrom(this.resourceClass);
}
}
}
public class Registry {
public static final String BUCKET_GIF = "Gif";
public static final String BUCKET_BITMAP = "Bitmap";
public static final String BUCKET_BITMAP_DRAWABLE = "BitmapDrawable";
private static final String BUCKET_PREPEND_ALL = "legacy_prepend_all";
private static final String BUCKET_APPEND_ALL = "legacy_append";
public Registry() {
setResourceDecoderBucketPriorityList(
Arrays.asList(BUCKET_GIF, BUCKET_BITMAP, BUCKET_BITMAP_DRAWABLE));
}
//所以ResourceDecoderRegistry的bucketPriorityList的值为[BUCKET_PREPEND_ALL,BUCKET_GIF,BUCKET_BITMAP,BUCKET_BITMAP_DRAWABLE,BUCKET_APPEND_ALL]
public final Registry setResourceDecoderBucketPriorityList(@NonNull List buckets) {
List modifiedBuckets = new ArrayList<>(buckets.size());
modifiedBuckets.addAll(buckets);
modifiedBuckets.add(0, BUCKET_PREPEND_ALL);
modifiedBuckets.add(BUCKET_APPEND_ALL);
decoderRegistry.setBucketPriorityList(modifiedBuckets);
return this;
}
}
decoders以bucket为key，List
//ResouceDecoderRegistry
private synchronized List> getOrAddEntryList(@NonNull String bucket) {
if (!bucketPriorityList.contains(bucket)) {
bucketPriorityList.add(bucket);
}
List> entries = decoders.get(bucket);
if (entries == null) {
entries = new ArrayList<>();
decoders.put(bucket, entries);
}
return entries;
}
public synchronized void append(@NonNull String bucket,
@NonNull ResourceDecoder decoder,
@NonNull Class dataClass, @NonNull Class resourceClass) {
//将Entry添加到key为bucket的List里
getOrAddEntryList(bucket).add(new Entry<>(dataClass, resourceClass, decoder));
}
//Registry
public Registry append(
@NonNull String bucket,
@NonNull Class dataClass,
@NonNull Class resourceClass,
@NonNull ResourceDecoder decoder) {
decoderRegistry.append(bucket, decoder, dataClass, resourceClass);
return this;
}
Glide(){
registry
/* Bitmaps */
.append(Registry.BUCKET_BITMAP, InputStream.class, Bitmap.class, streamBitmapDecoder)
/* BitmapDrawables */
.append(
Registry.BUCKET_BITMAP_DRAWABLE,
InputStream.class,
BitmapDrawable.class,
new BitmapDrawableDecoder<>(resources, streamBitmapDecoder))
/* GIFs */
.append(
Registry.BUCKET_GIF,
InputStream.class,
GifDrawable.class,
new StreamGifDecoder(imageHeaderParsers, byteBufferGifDecoder, arrayPool))
}
getTranscodeClasses()
熟悉的名字，熟悉的味道，这个类比上面那两个简单，自己按照规则看下就懂了。
public class TranscoderRegistry {
private final List> transcoders = new ArrayList<>();
public synchronized void register(
@NonNull Class decodedClass, @NonNull Class transcodedClass,
@NonNull ResourceTranscoder transcoder) {
transcoders.add(new Entry<>(decodedClass, transcodedClass, transcoder));
}
public synchronized List> getTranscodeClasses(
@NonNull Class resourceClass, @NonNull Class transcodeClass) {
List> transcodeClasses = new ArrayList<>();
//如果transcodeClass是resourceClass的父类（比如Drawable是BitmapDrawable和GifDrawable的父类）则为true。
//所以如果resourceClass传入的是Drawable的子类，则最终只会添加Drawable.class
if (transcodeClass.isAssignableFrom(resourceClass)) {
transcodeClasses.add(transcodeClass);
return transcodeClasses;
}
for (Entry entry : transcoders) {
if (entry.handles(resourceClass, transcodeClass)) {
//这里有效的是当传入Bitmap.class和Drawable.class的时候，所以最后会添加Drawable.calss
transcodeClasses.add(transcodeClass);
}
}
return transcodeClasses;
}
private static final class Entry {
private final Class fromClass;
private final Class toClass;
@Synthetic
final ResourceTranscoder transcoder;
Entry(@NonNull Class fromClass, @NonNull Class toClass,
@NonNull ResourceTranscoder transcoder) {
this.fromClass = fromClass;
this.toClass = toClass;
this.transcoder = transcoder;
}
public boolean handles(@NonNull Class fromClass, @NonNull Class toClass) {
return this.fromClass.isAssignableFrom(fromClass) && toClass.isAssignableFrom(this.toClass);
}
}
}
//Registry
public Registry register(
@NonNull Class resourceClass, @NonNull Class transcodeClass,
@NonNull ResourceTranscoder transcoder) {
transcoderRegistry.register(resourceClass, transcodeClass, transcoder);
return this;
}
//Glide
Glide(){
registry
/* Transcoders */
.register(
Bitmap.class,
BitmapDrawable.class,
new BitmapDrawableTranscoder(resources))
}
getTransformation()
Transformation是一个接口，继承了Key接口，同时自己有一个transform方法，用来将Resource转换为另一个Resource。比如它的实现类CenterCrop，就是将Bitmap转为centerCrop样子的Bitmap。
getTransformation()则根据之前在transformations存好的键值对来获取Transformation。
Transformation getTransformation(Class resourceClass) {
Transformation result = (Transformation) transformations.get(resourceClass); //由BaseRequestOptions的transformations传递进来
if (result == null) {
for (Entry, Transformation> entry : transformations.entrySet()) {
if (entry.getKey().isAssignableFrom(resourceClass)) {
result = (Transformation) entry.getValue();
break;
}
}
}
if (result == null) {
if (transformations.isEmpty() && isTransformationRequired) {
throw new IllegalArgumentException(
"Missing transformation for " + resourceClass + ". If you wish to"
+ " ignore unknown resource types, use the optional transformation methods.");
} else {
return UnitTransformation.get(); //这个默认返回原Resource，不做转换
}
}
return result;
}
在我们使用RequestBuilder显式调用centerCrop()或者其他转换时，最终会将对应的类型和Transformation存进transformations。如果没有显式调用，但是ImageView本身设置了转换的（比如设置了android:scaleType="centerCrop"），会在into()时进行设置存进transformations。
Glide.with(this)
.load("")
.centerCrop()
.into(imageView);
//BaseRequestOptions
public T centerCrop() {
return transform(DownsampleStrategy.CENTER_OUTSIDE, new CenterCrop());
}
final T transform(@NonNull DownsampleStrategy downsampleStrategy,
@NonNull Transformation transformation) {
if (isAutoCloneEnabled) {
//在clone()中会设置isAutoCloneEnabled为false，所以最终还是会走到下面的语句
return clone().transform(downsampleStrategy, transformation);
}
downsample(downsampleStrategy);
return transform(transformation);
}
public T transform(@NonNull Transformation transformation) {
return transform(transformation, /*isRequired=*/ true);
}
T transform(
@NonNull Transformation transformation, boolean isRequired) {
if (isAutoCloneEnabled) {
return clone().transform(transformation, isRequired);
}
DrawableTransformation drawableTransformation =
new DrawableTransformation(transformation, isRequired);
//最终transformations添加的键值对为下面这些
transform(Bitmap.class, transformation, isRequired);
transform(Drawable.class, drawableTransformation, isRequired);
transform(BitmapDrawable.class, drawableTransformation.asBitmapDrawable(), isRequired);
transform(GifDrawable.class, new GifDrawableTransformation(transformation), isRequired);
return selfOrThrowIfLocked();
}
T transform(
@NonNull Class resourceClass,
@NonNull Transformation transformation,
boolean isRequired) {
if (isAutoCloneEnabled) {
return clone().transform(resourceClass, transformation, isRequired);
}
transformations.put(resourceClass, transformation); //在这里添加进去
fields |= TRANSFORMATION;
isTransformationAllowed = true;
fields |= TRANSFORMATION_ALLOWED;
// Always set to false here. Known scale only transformations will call this method and then
// set isScaleOnlyOrNoTransform to true immediately after.
isScaleOnlyOrNoTransform = false;
if (isRequired) {
fields |= TRANSFORMATION_REQUIRED;
isTransformationRequired = true;
}
return selfOrThrowIfLocked();
}
hasLoadPath()
LoadPath主要是封装了List
在getLoadPath中首先从缓存中获取，如果没获取到则会继续获取decodePaths，如果decodePaths不为空，则创建一个新的LoadPath并传入缓存，最后返回。
//DecodeHelper
boolean hasLoadPath(Class dataClass) {
return getLoadPath(dataClass) != null;
}
//Registry
LoadPath getLoadPath(Class dataClass) {
return glideContext.getRegistry().getLoadPath(dataClass, resourceClass, transcodeClass);
}
public LoadPath getLoadPath(
@NonNull Class dataClass, @NonNull Class resourceClass,
@NonNull Class transcodeClass) {
LoadPath result =
loadPathCache.get(dataClass, resourceClass, transcodeClass);
if (loadPathCache.isEmptyLoadPath(result)) {
//返回的是一个特定的LoadPath，代表之前没有发现可用的LoadPath。
//当下面的decodePaths.isEmpty()时，loadPathCache存入的result为null，这时实际存入的是一个特定的NO_PATHS_SIGNAL。
return null;
} else if (result == null) {
List> decodePaths =
getDecodePaths(dataClass, resourceClass, transcodeClass);
if (decodePaths.isEmpty()) {
//从给定的数据类中可能无法解码或转码为所需的类型。
result = null;
} else {
result = new LoadPath<>(
dataClass, resourceClass, transcodeClass, decodePaths, throwableListPool);
}
loadPathCache.put(dataClass, resourceClass, transcodeClass, result);
}
return result;
}
//DecodePath则主是封装List>和ResourceTranscoder transcoder来进行解码和转码工作
private List> getDecodePaths(
@NonNull Class dataClass/*InputStream.class*/, @NonNull Class resourceClass/*Object.class*/,
@NonNull Class transcodeClass/*Drawable.class*/) {
List> decodePaths = new ArrayList<>();
//这些getXXXClasses获取上面都有说过
List> registeredResourceClasses =
decoderRegistry.getResourceClasses(dataClass, resourceClass); //GifDrawable.class、Bitmap.class、BitmapDrawable.class
for (Class registeredResourceClass : registeredResourceClasses) {
List> registeredTranscodeClasses =
transcoderRegistry.getTranscodeClasses(registeredResourceClass, transcodeClass); //Drawable.class
for (Class registeredTranscodeClass : registeredTranscodeClasses) {
List> decoders =
decoderRegistry.getDecoders(dataClass, registeredResourceClass); //StreamGifDecoder、BitmapDrawableDecoder
ResourceTranscoder transcoder =
transcoderRegistry.get(registeredResourceClass, registeredTranscodeClass); //BitmapDrawableTranscoder
@SuppressWarnings("PMD.AvoidInstantiatingObjectsInLoops")
DecodePath path =
new DecodePath<>(dataClass/*InputStream.class*/, registeredResourceClass/*Bitmap.class*/, registeredTranscodeClass/*Drawable.class*/,
decoders/*StreamGifDecoder、BitmapDrawableDecoder*/, transcoder/*BitmapDrawableTranscoder*/, throwableListPool);
decodePaths.add(path);
}
}
return decodePaths;
}
getDiskCache()
获取磁盘缓存，具体请看Glide源码解析之DiskCache
DiskCache getDiskCache() {
return diskCacheProvider.getDiskCache();
}