1. 前言
首先,LPL赛区S9再度夺冠,让我们恭喜FPX凤凰涅槃!
好长好长一段时间没有写博客了,中间经历了很多很多事. 比较庆幸的是找到了一份满意的工作.现在工作空闲之余,又可以写写博客归纳总结了.
图片加载可能是现在所有APP都必备的,当然有很多选择,可以自己写一个库用来展示网络图片.也可以用Glide,Fresco,Picasso等等.Glide由于我们公司在用,而且这是谷歌也推荐的一个图片加载库,用了也很久了,一直没有去研究它的底层实现逻辑.这次一定要好好研究研究.毕竟,需要用到图片加载的地方实在太多了.
关于如何阅读源码,郭神以前总结过8个字:抽丝剥茧、点到即止.意思就是我们在看的时候,抓关键,主流程,不要沉迷在代码细节中无法自拔.本篇文章主要着重于展示网络图片主流程,代码细节就不展开了,实在是太庞大太庞大了,而且细节贼多....
查看Glide源码的方式很简单,新建一个demo,然后通过gradle引入Glide,然后就可以愉快的查看源码了.
ps: 下面所用到的源码是属于Glide 4.8.0的,引入Glide: implementation 'com.github.bumptech.glide:glide:4.8.0'
2. 阅读前准备
总所周知,Glide加载图片的基本方式是Glide.with(context).load(url).into(imageView);,三步走. 那么我们阅读主流程也是跟着这三步走,去看一下主流程是怎么实现的.
3. with()
鼠标左键+Ctrl,点击with方法.
public static RequestManager with(@NonNull Activity activity) {
//分析2
return getRetriever(activity).get(activity);
}
public static RequestManager with(@NonNull FragmentActivity activity) {
return getRetriever(activity).get(activity);
}
public static RequestManager with(@NonNull Fragment fragment) {
return getRetriever(fragment.getActivity()).get(fragment);
}
public static RequestManager with(@NonNull View view) {
return getRetriever(view.getContext()).get(view);
}
private static RequestManagerRetriever getRetriever(@Nullable Context context) {
//分析1 Glide单例
return Glide.get(context).getRequestManagerRetriever();
}
public RequestManagerRetriever getRequestManagerRetriever() {
return requestManagerRetriever;
}
首先分析1处进行Glide初始化,它其实里面是通过GlideBuilder进行的初始化
Glide build(@NonNull Context context) {
//加载资源线程池 包括从网络加载
if (sourceExecutor == null) {
sourceExecutor = GlideExecutor.newSourceExecutor();
}
//磁盘缓存线程池
if (diskCacheExecutor == null) {
diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
}
//动画线程池
if (animationExecutor == null) {
animationExecutor = GlideExecutor.newAnimationExecutor();
}
if (memorySizeCalculator == null) {
memorySizeCalculator = new MemorySizeCalculator.Builder(context).build();
}
if (connectivityMonitorFactory == null) {
connectivityMonitorFactory = new DefaultConnectivityMonitorFactory();
}
if (bitmapPool == null) {
int size = memorySizeCalculator.getBitmapPoolSize();
if (size > 0) {
bitmapPool = new LruBitmapPool(size);
} else {
bitmapPool = new BitmapPoolAdapter();
}
}
if (arrayPool == null) {
arrayPool = new LruArrayPool(memorySizeCalculator.getArrayPoolSizeInBytes());
}
if (memoryCache == null) {
memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());
}
if (diskCacheFactory == null) {
diskCacheFactory = new InternalCacheDiskCacheFactory(context);
}
if (engine == null) {
//注意,这里有一个引擎,后面会使用到
engine =
new Engine(
memoryCache,
diskCacheFactory,
diskCacheExecutor,
sourceExecutor,
GlideExecutor.newUnlimitedSourceExecutor(),
GlideExecutor.newAnimationExecutor(),
isActiveResourceRetentionAllowed);
}
RequestManagerRetriever requestManagerRetriever =
new RequestManagerRetriever(requestManagerFactory);
return new Glide(
context,
engine,
memoryCache,
bitmapPool,
arrayPool,
requestManagerRetriever,
connectivityMonitorFactory,
logLevel,
defaultRequestOptions.lock(),
defaultTransitionOptions);
}
Glide就是初始化一些线程池,引擎什么的,稍后会用到.
再从分析2处可以看到,Glide 有很多重载方法,但是都是调用的RequestManagerRetriever的get方法,下面我们随便看一个RequestManagerRetriever的get重载方法
public RequestManager get(@NonNull Activity activity) {
//如果是子线程,那么生命周期就很长,和application一样,当然,这些是细节,别去影响主流程的阅读
if (Util.isOnBackgroundThread()) {
return get(activity.getApplicationContext());
} else {
assertNotDestroyed(activity);
android.app.FragmentManager fm = activity.getFragmentManager();
return fragmentGet(
activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
}
}
public RequestManager get(@NonNull Context context) {
if (context == null) {
throw new IllegalArgumentException("You cannot start a load on a null Context");
} else if (Util.isOnMainThread() && !(context instanceof Application)) {
//这些都会调用get方法
if (context instanceof FragmentActivity) {
return get((FragmentActivity) context);
} else if (context instanceof Activity) {
return get((Activity) context);
} else if (context instanceof ContextWrapper) {
return get(((ContextWrapper) context).getBaseContext());
}
}
//创建一个生命周期是application相同的RequestManager
return getApplicationManager(context);
}
public RequestManager get(@NonNull FragmentActivity activity) {
if (Util.isOnBackgroundThread()) {
return get(activity.getApplicationContext());
} else {
assertNotDestroyed(activity);
FragmentManager fm = activity.getSupportFragmentManager();
return supportFragmentGet(
activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
}
}
private RequestManager getApplicationManager(@NonNull Context context) {
if (applicationManager == null) {
synchronized (this) {
if (applicationManager == null) {
Glide glide = Glide.get(context.getApplicationContext());
applicationManager =
factory.build(
glide,
new ApplicationLifecycle(),
new EmptyRequestManagerTreeNode(),
context.getApplicationContext());
}
}
}
return applicationManager;
}
上面得分2种情况,一种是非application,一种是传入的是application.这两种情况下的生命周期是不太一样的,非application的会调用下面的fragmentGet方法创建一个fragment观察activity的生命周期,即activity销毁,那么图片就不会继续加载,释放资源等.而传入的是application的话,生命周期就和application一样了.
private RequestManager fragmentGet(@NonNull Context context,
@NonNull android.app.FragmentManager fm,
@Nullable android.app.Fragment parentHint,
boolean isParentVisible) {
RequestManagerFragment current = getRequestManagerFragment(fm, parentHint, isParentVisible);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
Glide glide = Glide.get(context);
requestManager =
factory.build(
glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
//给这个fragment设置一个RequestManager
current.setRequestManager(requestManager);
}
return requestManager;
}
private RequestManagerFragment getRequestManagerFragment(
@NonNull final android.app.FragmentManager fm,
@Nullable android.app.Fragment parentHint,
boolean isParentVisible) {
...
//构建一个空fragment
RequestManagerFragment current = new RequestManagerFragment();
current.setParentFragmentHint(parentHint);
if (isParentVisible) {
current.getGlideLifecycle().onStart();
}
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
...
return current;
}
可以看到,如果传入的是非application那么就去构建一个fragment用于观察加载的那张图片的所在activity的生命周期,如果已经销毁了,那么肯定就没必要再加载了.最后with返回的是RequestManager.with这里知道这些就OK了.
4. load()
再开看load方法,它是with返回的RequestManager里面的方法.
public RequestBuilder<Drawable> load(@Nullable String string) {
return asDrawable().load(string);
}
public RequestBuilder<Drawable> asDrawable() {
return as(Drawable.class);
}
public <ResourceType> RequestBuilder<ResourceType> as(
@NonNull Class<ResourceType> resourceClass) {
return new RequestBuilder<>(glide, this, resourceClass, context);
}
load方法里面调用的asDrawable(),主要是初始化RequestBuilder
protected RequestBuilder(Glide glide, RequestManager requestManager,
Class<TranscodeType> transcodeClass, Context context) {
this.glide = glide;
this.requestManager = requestManager;
//注意,这里传入的是Drawable.class
this.transcodeClass = transcodeClass;
this.defaultRequestOptions = requestManager.getDefaultRequestOptions();
this.context = context;
this.transitionOptions = requestManager.getDefaultTransitionOptions(transcodeClass);
this.requestOptions = defaultRequestOptions;
this.glideContext = glide.getGlideContext();
}
public RequestBuilder<TranscodeType> load(@Nullable String string) {
return loadGeneric(string);
}
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
this.model = model;
isModelSet = true;
return this;
}
然后调用load进行model的赋值.load流程走完了,就是创建了一个RequestBuilder
5. into()
下面就比较复杂了,我找网络通信的代码找了特别久才找到了,看Glide源码看得欲仙欲死.如郭神所说,into方法里面有着成吨的操作.各种复杂逻辑.前面load流程走完了是返回了一个RequestBuilder,那么into方法就是在RequestBuilder里面的.
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
Util.assertMainThread();
Preconditions.checkNotNull(view);
RequestOptions requestOptions = this.requestOptions;
if (!requestOptions.isTransformationSet()
&& requestOptions.isTransformationAllowed()
&& view.getScaleType() != null) {
switch (view.getScaleType()) {
case CENTER_CROP:
requestOptions = requestOptions.clone().optionalCenterCrop();
break;
case CENTER_INSIDE:
requestOptions = requestOptions.clone().optionalCenterInside();
break;
case FIT_CENTER:
case FIT_START:
case FIT_END:
requestOptions = requestOptions.clone().optionalFitCenter();
break;
case FIT_XY:
requestOptions = requestOptions.clone().optionalCenterInside();
break;
case CENTER:
case MATRIX:
default:
// Do nothing.
}
}
//这里的transcodeClass是前面的Drawable.class
return into(
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions);
}
into成吨的逻辑,从最后一行开始.首先进入GlideContext的buildImageViewTarget方法.
public <X> ViewTarget<ImageView, X> buildImageViewTarget(
@NonNull ImageView imageView, @NonNull Class<X> transcodeClass) {
return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
}
public class ImageViewTargetFactory {
@NonNull
@SuppressWarnings("unchecked")
public <Z> ViewTarget<ImageView, Z> buildTarget(@NonNull ImageView view,
@NonNull Class<Z> clazz) {
if (Bitmap.class.equals(clazz)) {
return (ViewTarget<ImageView, Z>) new BitmapImageViewTarget(view);
} else if (Drawable.class.isAssignableFrom(clazz)) {
return (ViewTarget<ImageView, Z>) new DrawableImageViewTarget(view);
} else {
throw new IllegalArgumentException(
"Unhandled class: " + clazz + ", try .as*(Class).transcode(ResourceTranscoder)");
}
}
}
毫无疑问,这里创建的是DrawableImageViewTarget.然后DrawableImageViewTarget被作为参数传入into方法.
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
@NonNull RequestOptions options) {
...
//分析1
Request request = buildRequest(target, targetListener, options);
...
requestManager.clear(target);
target.setRequest(request);
//分析2
requestManager.track(target, request);
return target;
}
分析1处,通过buildRequest构建一个Request,最后会走到RequestBuilder的obtainRequest方法构建一个SingleRequest.
private Request obtainRequest(
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
RequestOptions requestOptions,
RequestCoordinator requestCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight) {
return SingleRequest.obtain(
context,
glideContext,
//String
model,
//Drawable.class
transcodeClass,
//options
requestOptions,
//宽高
overrideWidth,
overrideHeight,
priority,
//DrawableImageViewTarget
target,
targetListener,
requestListeners,
requestCoordinator,
glideContext.getEngine(),
transitionOptions.getTransitionFactory());
}
省略了很多处理缩略图的逻辑,直接到最后构建SingleRequest. 这个Request也就是我们要进行的请求,猜测大部分逻辑都是在这里面.
继续回到分析2处,requestManager.track(target, request);
void track(@NonNull Target<?> target, @NonNull Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}
//RequestTracker.java
public void runRequest(@NonNull Request request) {
requests.add(request);
if (!isPaused) {
//开始搞事情
request.begin();
} else {
request.clear();
pendingRequests.add(request);
}
}
调用了Request的begin,看样子是要开始了,上面分析了这里是SingleRequest,所以直接看SingleRequest的begin().
public void begin() {
......
if (status == Status.COMPLETE) {
//已加载完成 回调
onResourceReady(resource, DataSource.MEMORY_CACHE);
return;
}
status = Status.WAITING_FOR_SIZE;
//测量一下ImageView的大小
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
if ((status == Status.RUNNING || status == Status.WAITING_FOR_SIZE)
&& canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
}
}
测量一下ImageView的大小,如果在调用Glide加载图片时设置override设置宽高,那么直接会走onSizeReady方法处.如果没有写,那么走target.getSize(this);测量一下宽高,然后在里面还是会调用SingleRequest的onSizeReady()方法.
public void onSizeReady(int width, int height) {
......
status = Status.RUNNING;
float sizeMultiplier = requestOptions.getSizeMultiplier();
this.width = maybeApplySizeMultiplier(width, sizeMultiplier);
this.height = maybeApplySizeMultiplier(height, sizeMultiplier);
//开始用引擎
loadStatus = engine.load(
glideContext,
model,
requestOptions.getSignature(),
this.width,
this.height,
requestOptions.getResourceClass(),
transcodeClass,
priority,
requestOptions.getDiskCacheStrategy(),
requestOptions.getTransformations(),
requestOptions.isTransformationRequired(),
requestOptions.isScaleOnlyOrNoTransform(),
requestOptions.getOptions(),
requestOptions.isMemoryCacheable(),
requestOptions.getUseUnlimitedSourceGeneratorsPool(),
requestOptions.getUseAnimationPool(),
requestOptions.getOnlyRetrieveFromCache(),
this);
}
开始用引擎load
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) {
EngineKey key = keyFactory.buildKey(model, signature, width, height, transformations,
resourceClass, transcodeClass, options);
//从弱引用中找,有就直接返回
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;
}
//缓存中
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;
}
//查找之前缓存的EngineJob
EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
if (current != null) {
current.addCallback(cb);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new LoadStatus(cb, current);
}
//engineJob是为decodeJob干事情的,管理下载过程以及状态
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
DecodeJob<R> decodeJob =
decodeJobFactory.build(
glideContext,
model,
key,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
onlyRetrieveFromCache,
options,
engineJob);
jobs.put(key, engineJob);
//注册ResourceCallback
engineJob.addCallback(cb);
//开始真正的工作
engineJob.start(decodeJob);
return new LoadStatus(cb, engineJob);
}
首先是从各种缓存中拿之前的数据,有则返回,没有则创建DecodeJob开始工作.
//EngineJob.java
public void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
GlideExecutor executor = decodeJob.willDecodeFromCache()
? diskCacheExecutor
: getActiveSourceExecutor();
executor.execute(decodeJob);
}
我们这里暂时不考虑缓存的情况,那么使用的这里使用的GlideExecutor是GlideBuilder的build方法中初始化的sourceExecutor = GlideExecutor.newSourceExecutor();其实就是一个线程池. 然后DecodeJob是Runnable,放到线程池中去执行,所以我们知道找重点,去DecodeJob的run方法看
public void run() {
DataFetcher<?> localFetcher = currentFetcher;
try {
//已经取消
if (isCancelled) {
notifyFailed();
return;
}
//重点 这里是执行
runWrapped();
} catch (Throwable t) {
} finally {
}
}
private enum Stage {
/** The initial stage. */
INITIALIZE,
/** Decode from a cached resource. */
RESOURCE_CACHE,
/** Decode from cached source data. */
DATA_CACHE,
/** Decode from retrieved source. */
SOURCE,
/** Encoding transformed resources after a successful load. */
ENCODE,
/** No more viable stages. */
FINISHED,
}
private void runWrapped() {
//runReason在DecodeJob初始化的时候初始值是INITIALIZE,上面没有带大家看,这不是重点.
switch (runReason) {
case INITIALIZE:
//获取下一个state
stage = getNextStage(Stage.INITIALIZE);
//这里会去获取一个SourceGenerator
currentGenerator = getNextGenerator();
runGenerators();
break;
case SWITCH_TO_SOURCE_SERVICE:
runGenerators();
break;
case DECODE_DATA:
decodeFromRetrievedData();
break;
default:
throw new IllegalStateException("Unrecognized run reason: " + runReason);
}
}
//一次完整的请求,会把这里的都走完.
private DataFetcherGenerator getNextGenerator() {
switch (stage) {
case RESOURCE_CACHE:
return new ResourceCacheGenerator(decodeHelper, this);
case DATA_CACHE:
return new DataCacheGenerator(decodeHelper, this);
case SOURCE:
//会走到这里
return new SourceGenerator(decodeHelper, this);
case FINISHED:
return null;
default:
throw new IllegalStateException("Unrecognized stage: " + stage);
}
}
private void runGenerators() {
currentThread = Thread.currentThread();
startFetchTime = LogTime.getLogTime();
boolean isStarted = false;
while (!isCancelled && currentGenerator != null
//重点
&& !(isStarted = currentGenerator.startNext())) {
stage = getNextStage(stage);
currentGenerator = getNextGenerator();
if (stage == Stage.SOURCE) {
reschedule();
return;
}
}
// We've run out of stages and generators, give up.
if ((stage == Stage.FINISHED || isCancelled) && !isStarted) {
notifyFailed();
}
}
Glide定义了几个步骤,在枚举类Stage里面.这是每一步的状态,当执行完一个状态的时候,又去获取下一个状态进行执行相应的逻辑.在runGenerators方法里面有一个while控制.我们第一步是SourceGenerator,所以会走到SourceGenerator的startNext()里面.
//SourceGenerator.java
public boolean startNext() {
if (dataToCache != null) {
Object data = dataToCache;
dataToCache = null;
cacheData(data);
}
//有缓存
if (sourceCacheGenerator != null && sourceCacheGenerator.startNext()) {
return true;
}
sourceCacheGenerator = null;
loadData = null;
boolean started = false;
while (!started && hasNextModelLoader()) {
loadData = helper.getLoadData().get(loadDataListIndex++);
if (loadData != null
&& (helper.getDiskCacheStrategy().isDataCacheable(loadData.fetcher.getDataSource())
|| helper.hasLoadPath(loadData.fetcher.getDataClass()))) {
started = true;
//这里的fetcher是HttpUrlFetcher
loadData.fetcher.loadData(helper.getPriority(), this);
}
}
return started;
}
主流程是根据HttpUrlFetcher去加载数据,这里就不分析为啥HttpUrlFetcher,比较麻烦,篇幅收不住.
//HttpUrlFetcher.java
public void loadData(@NonNull Priority priority,
@NonNull DataCallback<? super InputStream> callback) {
try {
//看情况,这个方法是获取到了网络数据了 盲猜应该是请求网络了
InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
//将数据返回回去
callback.onDataReady(result);
} catch (IOException e) {
callback.onLoadFailed(e);
} finally {
}
}
终于,感觉要开始请求网络了,并且结果还通过回调回去了.来看一下loadDataWithRedirects方法
private InputStream loadDataWithRedirects(URL url, int redirects, URL lastUrl,
Map<String, String> headers) throws IOException {
if (redirects >= MAXIMUM_REDIRECTS) {
throw new HttpException("Too many (> " + MAXIMUM_REDIRECTS + ") redirects!");
} else {
// Comparing the URLs using .equals performs additional network I/O and is generally broken.
// See http://michaelscharf.blogspot.com/2006/11/javaneturlequals-and-hashcode-make.html.
try {
if (lastUrl != null && url.toURI().equals(lastUrl.toURI())) {
throw new HttpException("In re-direct loop");
}
} catch (URISyntaxException e) {
// Do nothing, this is best effort.
}
}
urlConnection = connectionFactory.build(url);
for (Map.Entry<String, String> headerEntry : headers.entrySet()) {
urlConnection.addRequestProperty(headerEntry.getKey(), headerEntry.getValue());
}
urlConnection.setConnectTimeout(timeout);
urlConnection.setReadTimeout(timeout);
urlConnection.setUseCaches(false);
urlConnection.setDoInput(true);
// Stop the urlConnection instance of HttpUrlConnection from following redirects so that
// redirects will be handled by recursive calls to this method, loadDataWithRedirects.
urlConnection.setInstanceFollowRedirects(false);
// Connect explicitly to avoid errors in decoders if connection fails.
urlConnection.connect();
// Set the stream so that it's closed in cleanup to avoid resource leaks. See #2352.
stream = urlConnection.getInputStream();
if (isCancelled) {
return null;
}
final int statusCode = urlConnection.getResponseCode();
if (isHttpOk(statusCode)) {
//重点 网络请求OK
return getStreamForSuccessfulRequest(urlConnection);
} else if (isHttpRedirect(statusCode)) {
String redirectUrlString = urlConnection.getHeaderField("Location");
if (TextUtils.isEmpty(redirectUrlString)) {
throw new HttpException("Received empty or null redirect url");
}
URL redirectUrl = new URL(url, redirectUrlString);
// Closing the stream specifically is required to avoid leaking ResponseBodys in addition
// to disconnecting the url connection below. See #2352.
cleanup();
return loadDataWithRedirects(redirectUrl, redirects + 1, url, headers);
} else if (statusCode == INVALID_STATUS_CODE) {
throw new HttpException(statusCode);
} else {
throw new HttpException(urlConnection.getResponseMessage(), statusCode);
}
}
private InputStream getStreamForSuccessfulRequest(HttpURLConnection urlConnection)
throws IOException {
if (TextUtils.isEmpty(urlConnection.getContentEncoding())) {
int contentLength = urlConnection.getContentLength();
stream = ContentLengthInputStream.obtain(urlConnection.getInputStream(), contentLength);
} else {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Got non empty content encoding: " + urlConnection.getContentEncoding());
}
stream = urlConnection.getInputStream();
}
return stream;
}
这个就比较熟悉了,就是通过HttpURLConnection进行的网络请求,并且结果就是通过urlConnection.getInputStream();拿到的.这里拿到了结果后,就返回了,然后就是上面的callback.onDataReady(result);进行回调,处理结果
//SourceGenerator.java
public void onDataReady(Object data) {
DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy();
if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) {
dataToCache = data;
cb.reschedule();
} else {
//没有缓存 走这里
//这里的cb是上面private DataFetcherGenerator getNextGenerator()中初始化SourceGenerator时传入的DecodeJob
cb.onDataFetcherReady(loadData.sourceKey, data, loadData.fetcher,
loadData.fetcher.getDataSource(), originalKey);
}
}
//DecodeJob.java
public void onDataFetcherReady(Key sourceKey, Object data, DataFetcher<?> fetcher,
DataSource dataSource, Key attemptedKey) {
....
if (Thread.currentThread() != currentThread) {
runReason = RunReason.DECODE_DATA;
callback.reschedule(this);
} else {
GlideTrace.beginSection("DecodeJob.decodeFromRetrievedData");
try {
//上面的都不看了,会走到这里来
decodeFromRetrievedData();
} finally {
GlideTrace.endSection();
}
}
}
private void decodeFromRetrievedData() {
Resource<R> resource = null;
try {
//重点1
//从数据中解码得到资源
resource = decodeFromData(currentFetcher, currentData, currentDataSource);
} catch (GlideException e) {
e.setLoggingDetails(currentAttemptingKey, currentDataSource);
throwables.add(e);
}
if (resource != null) {
//重点2
notifyEncodeAndRelease(resource, currentDataSource);
} else {
runGenerators();
}
}
拿到数据之后,经过了几个方法,到了重点1处,开始从数据中解码.
private <Data> Resource<R> decodeFromData(DataFetcher<?> fetcher, Data data,
DataSource dataSource) throws GlideException {
try {
//这里又把解码包了一下
Resource<R> result = decodeFromFetcher(data, dataSource);
return result;
} finally {
fetcher.cleanup();
}
}
private <Data> Resource<R> decodeFromFetcher(Data data, DataSource dataSource)
throws GlideException {
LoadPath<Data, ?, R> path = decodeHelper.getLoadPath((Class<Data>) data.getClass());
//重点代码
//将解码交给LoadPath对象去搞
return runLoadPath(data, dataSource, path);
}
private <Data, ResourceType> Resource<R> runLoadPath(Data data, DataSource dataSource,
LoadPath<Data, ResourceType, R> path) throws GlideException {
Options options = getOptionsWithHardwareConfig(dataSource);
//将数据又包装了一下,,,,,,好多好多包装啊
DataRewinder<Data> rewinder = glideContext.getRegistry().getRewinder(data);
try {
// ResourceType in DecodeCallback below is required for compilation to work with gradle.
//在LoadPath对象中load 解码
return path.load(
rewinder, options, width, height, new DecodeCallback<ResourceType>(dataSource));
} finally {
rewinder.cleanup();
}
}
各种包装,各种转,最后将数据交给LoadPath对象对象去解码.
public Resource<Transcode> load(DataRewinder<Data> rewinder, @NonNull Options options, int width,
int height, DecodePath.DecodeCallback<ResourceType> decodeCallback) throws GlideException {
List<Throwable> throwables = Preconditions.checkNotNull(listPool.acquire());
try {
//核心代码
return loadWithExceptionList(rewinder, options, width, height, decodeCallback, throwables);
} finally {
listPool.release(throwables);
}
}
private Resource<Transcode> loadWithExceptionList(DataRewinder<Data> rewinder,
@NonNull Options options,
int width, int height, DecodePath.DecodeCallback<ResourceType> decodeCallback,
List<Throwable> exceptions) throws GlideException {
Resource<Transcode> result = null;
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = decodePaths.size(); i < size; i++) {
DecodePath<Data, ResourceType, Transcode> path = decodePaths.get(i);
try {
//核心代码
//将解码任务又转给了DecodePath去做 我擦,,,,转了好几手了
result = path.decode(rewinder, width, height, options, decodeCallback);
} catch (GlideException e) {
exceptions.add(e);
}
if (result != null) {
break;
}
}
return result;
}
又转了一手,到DecodePath手中去解码
public Resource<Transcode> decode(DataRewinder<DataType> rewinder, int width, int height,
@NonNull Options options, DecodeCallback<ResourceType> callback) throws GlideException {
Resource<ResourceType> decoded = decodeResource(rewinder, width, height, options);
Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
return transcoder.transcode(transformed, options);
}
private Resource<ResourceType> decodeResource(DataRewinder<DataType> rewinder, int width,
int height, @NonNull Options options) throws GlideException {
List<Throwable> exceptions = Preconditions.checkNotNull(listPool.acquire());
try {
//->
return decodeResourceWithList(rewinder, width, height, options, exceptions);
} finally {
listPool.release(exceptions);
}
}
private Resource<ResourceType> decodeResourceWithList(DataRewinder<DataType> rewinder, int width,
int height, @NonNull Options options, List<Throwable> exceptions) throws GlideException {
Resource<ResourceType> result = null;
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = decoders.size(); i < size; i++) {
ResourceDecoder<DataType, ResourceType> decoder = decoders.get(i);
try {
DataType data = rewinder.rewindAndGet();
if (decoder.handles(data, options)) {
data = rewinder.rewindAndGet();
//终于在这里开始解码了....
//根据DataType, ResourceType区别,分发给不同的解码器
result = decoder.decode(data, width, height, options);
}
// Some decoders throw unexpectedly. If they do, we shouldn't fail the entire load path, but
// instead log and continue. See #2406 for an example.
} catch (IOException | RuntimeException | OutOfMemoryError e) {
exceptions.add(e);
}
if (result != null) {
break;
}
}
return result;
}
终于在这里开始调用解码器开始解码了,,,,上面的decoder其实是StreamBitmapDecoder,在初始化Glide的时候就初始化好了....一直放那里没用它.来看StreamBitmapDecoder的decode方法
public Resource<Bitmap> decode(@NonNull InputStream source, int width, int height,
@NonNull Options options)
throws IOException {
...
//这里又将解码任务交给了Downsampler
return downsampler.decode(invalidatingStream, width, height, options, callbacks);
}
//Downsampler.java
public Resource<Bitmap> decode(InputStream is, int requestedWidth, int requestedHeight,
Options options, DecodeCallbacks callbacks) throws IOException {
Preconditions.checkArgument(is.markSupported(), "You must provide an InputStream that supports"
+ " mark()");
byte[] bytesForOptions = byteArrayPool.get(ArrayPool.STANDARD_BUFFER_SIZE_BYTES, byte[].class);
BitmapFactory.Options bitmapFactoryOptions = getDefaultOptions();
bitmapFactoryOptions.inTempStorage = bytesForOptions;
DecodeFormat decodeFormat = options.get(DECODE_FORMAT);
DownsampleStrategy downsampleStrategy = options.get(DownsampleStrategy.OPTION);
boolean fixBitmapToRequestedDimensions = options.get(FIX_BITMAP_SIZE_TO_REQUESTED_DIMENSIONS);
boolean isHardwareConfigAllowed =
options.get(ALLOW_HARDWARE_CONFIG) != null && options.get(ALLOW_HARDWARE_CONFIG);
try {
//-> 重点4
Bitmap result = decodeFromWrappedStreams(is, bitmapFactoryOptions,
downsampleStrategy, decodeFormat, isHardwareConfigAllowed, requestedWidth,
requestedHeight, fixBitmapToRequestedDimensions, callbacks);
// 解码得到Bitmap对象后，包装成BitmapResource对象返回，
// 通过内部的get方法得到Bitmap对象
return BitmapResource.obtain(result, bitmapPool);
} finally {
releaseOptions(bitmapFactoryOptions);
byteArrayPool.put(bytesForOptions);
}
}
解码任务又转手了,,,转到了Downsampler,
private Bitmap decodeFromWrappedStreams(InputStream is,
BitmapFactory.Options options, DownsampleStrategy downsampleStrategy,
DecodeFormat decodeFormat, boolean isHardwareConfigAllowed, int requestedWidth,
int requestedHeight, boolean fixBitmapToRequestedDimensions,
DecodeCallbacks callbacks) throws IOException {
...
//省去Bitmap压缩的代码
//通过BitmapFactory.decodeStream搞到Bitmap
Bitmap downsampled = decodeStream(is, options, callbacks, bitmapPool);
callbacks.onDecodeComplete(bitmapPool, downsampled);
//Bitmap旋转处理
....
return rotated;
}
Glide在拿到InputStream之后各种包装,各种转手,终于还是压缩处理之后通过BitmapFactory.decodeStream生成出Bitmap.最后这里是交给了Downsampler在处理,它的decode方法是返回到了DecodeJob的run方法，然后使用了notifyEncodeAndRelease()方法对Resource对象进行了回调.
//DecodeJob.java
private void notifyEncodeAndRelease(Resource<R> resource, DataSource dataSource) {
...
notifyComplete(result, dataSource);
...
}
private void notifyComplete(Resource<R> resource, DataSource dataSource) {
setNotifiedOrThrow();
//这里的callback其实是EngineJob,在初始化DecodeJob的时候传入的
callback.onResourceReady(resource, dataSource);
}
开始通过DecodeJob进行回调,然后又传到了EngineJob
//EngineJob.java
private static final Handler MAIN_THREAD_HANDLER =
new Handler(Looper.getMainLooper(), new MainThreadCallback());
public void onResourceReady(Resource<R> resource, DataSource dataSource) {
this.resource = resource;
this.dataSource = dataSource;
MAIN_THREAD_HANDLER.obtainMessage(MSG_COMPLETE, this).sendToTarget();
}
//MainThreadCallback#handleMessage
public boolean handleMessage(Message message) {
EngineJob<?> job = (EngineJob<?>) message.obj;
switch (message.what) {
case MSG_COMPLETE:
//-> 这里
job.handleResultOnMainThread();
break;
case MSG_EXCEPTION:
job.handleExceptionOnMainThread();
break;
case MSG_CANCELLED:
job.handleCancelledOnMainThread();
break;
default:
throw new IllegalStateException("Unrecognized message: " + message.what);
}
return true;
}
void handleResultOnMainThread() {
stateVerifier.throwIfRecycled();
if (isCancelled) {
resource.recycle();
release(false /*isRemovedFromQueue*/);
return;
} else if (cbs.isEmpty()) {
throw new IllegalStateException("Received a resource without any callbacks to notify");
} else if (hasResource) {
throw new IllegalStateException("Already have resource");
}
engineResource = engineResourceFactory.build(resource, isCacheable);
hasResource = true;
// Hold on to resource for duration of request so we don't recycle it in the middle of
// notifying if it synchronously released by one of the callbacks.
engineResource.acquire();
listener.onEngineJobComplete(this, key, engineResource);
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = cbs.size(); i < size; i++) {
ResourceCallback cb = cbs.get(i);
if (!isInIgnoredCallbacks(cb)) {
engineResource.acquire();
//关键代码 这里的cb是SingleRequest
cb.onResourceReady(engineResource, dataSource);
}
}
// Our request is complete, so we can release the resource.
engineResource.release();
release(false /*isRemovedFromQueue*/);
}
onResourceReady回调传回来的时候,通过handler切换到主线程,然后通过SingleRequest的onRrsourceReady方法将数据传递回去
public void onResourceReady(Resource<?> resource, DataSource dataSource) {
stateVerifier.throwIfRecycled();
loadStatus = null;
if (resource == null) {
GlideException exception = new GlideException("Expected to receive a Resource<R> with an "
+ "object of " + transcodeClass + " inside, but instead got null.");
onLoadFailed(exception);
return;
}
Object received = resource.get();
if (received == null || !transcodeClass.isAssignableFrom(received.getClass())) {
releaseResource(resource);
GlideException exception = new GlideException("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."));
onLoadFailed(exception);
return;
}
if (!canSetResource()) {
releaseResource(resource);
// We can't put the status to complete before asking canSetResource().
status = Status.COMPLETE;
return;
}
onResourceReady((Resource<R>) resource, (R) received, dataSource);
}
private void onResourceReady(Resource<R> resource, R result, DataSource dataSource) {
// We must call isFirstReadyResource before setting status.
boolean isFirstResource = isFirstReadyResource();
status = Status.COMPLETE;
this.resource = resource;
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);
//这里的target是初始化SingleRequest时传入的DrawableImageViewTarget
target.onResourceReady(result, animation);
}
} finally {
isCallingCallbacks = false;
}
notifyLoadSuccess();
}
在SingleRequest中做了一些判断,然后将数据传递给DrawableImageViewTarget去回调处理
//下面2个方法是DrawableImageViewTarget的父类ImageViewTarget中的
public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
if (transition == null || !transition.transition(resource, this)) {
setResourceInternal(resource);
} else {
maybeUpdateAnimatable(resource);
}
}
private void setResourceInternal(@Nullable Z resource) {
// Order matters here. Set the resource first to make sure that the Drawable has a valid and
// non-null Callback before starting it.
setResource(resource);
maybeUpdateAnimatable(resource);
}
//DrawableImageViewTarget.java
protected void setResource(@Nullable Drawable resource) {
view.setImageDrawable(resource);
}
这里的view就是我们在into时传入的ImageView对象....我擦,,,,终于把数据放到ImageView上了....不容易啊.
6. 总结
到这里,Glide的从网络加载图片到ImageView上的这个主流程是走完了.真的是成吨成吨的操作,各种复杂逻辑,各种封装,各种转换....看代码看得欲仙欲死....大量逻辑集中在into里面,很容易被绕晕..当然,我只是了解其中的主流程,细节真的太多太多了.
ps: 太久没写博客了,,,,感觉写的不是很好,这写的是什么垃圾玩意儿....
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