图片加载库-Glide源码分析

glide:3.7.0 使用

引入

  compile 'com.github.bumptech.glide:glide:3.7.0'

混淆

-keep public class * implements com.bumptech.glide.module.GlideModule
-keep public class * extends com.bumptech.glide.module.AppGlideModule
-keep public enum com.bumptech.glide.load.resource.bitmap.ImageHeaderParser$** {
  **[] $VALUES;
  public *;
}

# for DexGuard only
-keepresourcexmlelements manifest/application/meta-data@value=GlideModule

使用

使用的方式十分简单，和Picasso差不多

Glide.with(this).load("https://timgsa.baidu.com/timg?image&quality=80&size=b10000_10000&sec=1511148367&di=f2289ba7ce873fddd5e85dab9410ebeb&src=http%3A%2F%2Fi-1.yxdown.com%2F2013%2F11%2F6%2F94ba6d62-7676-4ced-abe0-0c6a279369f4.jpg")
.placeholder(R.drawable.ic_launcher_background)
.into(mIv);

同样也可以为他设置其他，例如 listener 、 centerCrop 、transform 、 sizeMultiplier

.listener(new RequestListener() {
                @Override
                public boolean onException(Exception e, String model, Target target, boolean isFirstResource) {
                    return false;
                }

                @Override
                public boolean onResourceReady(GlideDrawable resource, String model, Target target, boolean isFromMemoryCache, boolean isFirstResource) {
                    return false;
                }
            })

.centerCrop()

....

之类的，这些使用的方法和Picasso十分类似。

源码分析

RequestManager

Glide.with(context)

从 Glide.with 开始分析起。

public static RequestManager with(FragmentActivity activity) {
    RequestManagerRetriever retriever = RequestManagerRetriever.get();
    return retriever.get(activity);
}

先看看 RequestManagerRetriever.get() 方法都干了什么

private static final RequestManagerRetriever INSTANCE = new RequestManagerRetriever();

RequestManagerRetriever() {
    handler = new Handler(Looper.getMainLooper(), this /* Callback */);
}

上述的方其实就是 拿取了 RequestManagerRetriever 的单例对象。而这 RequestManagerRetriever 的构造函数所做的就只有 初始化 一个 handler ，这个handler 最终回调到主线程。

然后看看 retriever.get(activity)

public RequestManager get(Activity activity) {
    if (Util.isOnBackgroundThread() || Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
        return get(activity.getApplicationContext());
    } else {
        //判断activity是否已经是销毁状态
        assertNotDestroyed(activity);
        //获取FragmentManager 对象
        FragmentManager fm = activity.getSupportFragmentManager();
        //创建Fragment，RequestManager并将其绑定
        return supportFragmentGet(activity, fm);
    }
}

然后就 调用了 supportFragmentGet(activity, fm);

RequestManager supportFragmentGet(Context context, FragmentManager fm) {
    // 注 1 
    SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);
    // 注 2
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
        requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
        current.setRequestManager(requestManager);
    }
    return requestManager;
}

注 1 :

getSupportRequestManagerFragment 方法

SupportRequestManagerFragment getSupportRequestManagerFragment(final FragmentManager fm) {
    SupportRequestManagerFragment current = (SupportRequestManagerFragment) fm.findFragmentByTag(
        FRAGMENT_TAG);
    // 判断是否能从 fm 里面拿到Tag为FRAGMENT_TAG的SupportRequestManagerFragment
    if (current == null) {
        //current 为空 那么就从 pendingSupportRequestManagerFragments 里面拿取。pendingSupportRequestManagerFragments 其实是一个Map ，根据 fm 来获取 这个 创建过的 SupportRequestManagerFragment。
        current = pendingSupportRequestManagerFragments.get(fm);
         //如果没有就创建一个 SupportRequestManagerFragment ，并把他放在 pendingSupportRequestManagerFragments 里面。
        if (current == null) {
            current = new SupportRequestManagerFragment();
            pendingSupportRequestManagerFragments.put(fm, current);
            // 添加标记
            fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
            handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
        }
    }
    return current;
}

那么就看看 创建 SupportRequestManagerFragment 都干了什么

public SupportRequestManagerFragment() {
    this(new ActivityFragmentLifecycle());
}

@SuppressLint("ValidFragment")
public SupportRequestManagerFragment(ActivityFragmentLifecycle lifecycle) {
    this.lifecycle = lifecycle;
}

他会生成初始化一个 ActivityFragmentLifecycle 对象 。这个对象用于管理 Activity、Fragment 的生命周期的状态。而在SupportRequestManagerFragment类里面，我们可以看到有如下代码：

@Override
public void onStop() {
    super.onStop();
    lifecycle.onStop();
}

@Override
public void onDestroy() {
    super.onDestroy();
    lifecycle.onDestroy();
}

他会和生命周期关联上。而生命周期的状态全部交给了 ActivityFragmentLifecycle 这个类来实现。

注 2 ：

从 SupportRequestManagerFragment 里面获取 RequestManager 。 很明显 ，初始化的时候并没有创建 RequestManager 对象 ，那么就创建一个新的 RequestManager 对象 ，并设置给 SupportRequestManagerFragment 对象。

requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());

RequestManager 构造函数

RequestManager(Context context, final Lifecycle lifecycle, RequestManagerTreeNode treeNode,
        RequestTracker requestTracker, ConnectivityMonitorFactory factory) {
    this.context = context.getApplicationContext();
    this.lifecycle = lifecycle;
    this.treeNode = treeNode;
    this.requestTracker = requestTracker;
    //获取 Glide 实例 ，这又是一个单例对象
    this.glide = Glide.get(context);
    this.optionsApplier = new OptionsApplier();

    ....
}

新创建的 RequestManager 也绑定了 生命周期。

DrawableTypeRequest

那么 RequestManager 对象得以生成。 接下来我们最常的操作就是使用 load 方法 创建DrawableTypeRequest 对象了。

DrawableTypeRequest load = with.load("https://timgsa.baidu.com/timg?image&quality=80&size=b10000_10000&sec=1511148367&di=f2289ba7ce873fddd5e85dab9410ebeb&src=http%3A%2F%2Fi-1.yxdown.com%2F2013%2F11%2F6%2F94ba6d62-7676-4ced-abe0-0c6a279369f4.jpg");

RequestManager 类 里面的 load 方法

load 实现了很多个重载 load(byte[] model) 、load(String string) ..... ，所以会根据不同的参数来返回不同的 DrawableTypeRequest 这个泛型类。 下面就以 String 来分析。

public DrawableTypeRequest load(byte[] model) {
    return (DrawableTypeRequest) fromBytes().load(model);
}

public DrawableTypeRequest load(String string) {
    return (DrawableTypeRequest) fromString().load(string);
}

不同的参数 ， 就会执行不同的方法来生成 DrawableTypeRequest 对象 ，然后执行 load 方法 。

DrawableRequestBuilder.java

public DrawableRequestBuilder load(ModelType model) {
    // 交给父类处理
    super.load(model);
    return this;
}

GenericRequestBuilder.java

public GenericRequestBuilder load(ModelType model) {
    // model 赋值
    this.model = model;
    isModelSet = true;
    return this;
}

那么最后就生成了 DrawableTypeRequest 对象。利用这个对象我们可以设置 placeholder 、 listener 、error ...等

@Override
public DrawableRequestBuilder placeholder(Drawable drawable) {
    super.placeholder(drawable);
    return this;
}

@Override
public DrawableRequestBuilder listener(
        RequestListener requestListener) {
    super.listener(requestListener);
    return this;
}

@Override
public DrawableRequestBuilder error(Drawable drawable) {
    super.error(drawable);
    return this;
}

最后查看父类的代码，可以知道设置这些属性都是为 GenericRequestBuilder 的属性赋值。

public GenericRequestBuilder placeholder(
        Drawable drawable) {
    //为 placeholderDrawable 赋值
    this.placeholderDrawable = drawable;
    return this;
}

public GenericRequestBuilder listener(
        RequestListener requestListener) {
    //为 requestListener 赋值
    this.requestListener = requestListener;
    return this;
}

public GenericRequestBuilder error(
        Drawable drawable) {
    //为 errorPlaceholder 赋值
    this.errorPlaceholder = drawable;
    return this;
}

into

为 GenericRequestBuilder 的属性设置的差不多了 ，那么最后所要调用的 就是 into 这个方法。

DrawableRequestBuilder.java

@Override
public Target into(ImageView view) {
    return super.into(view);
}

GenericRequestBuilder.java

public Target into(ImageView view) {
    Util.assertMainThread();
    if (view == null) {
        throw new IllegalArgumentException("You must pass in a non null View");
    }

    if (!isTransformationSet && view.getScaleType() != null) {
        switch (view.getScaleType()) {
            case CENTER_CROP:
                applyCenterCrop();
                break;
            case FIT_CENTER:
            case FIT_START:
            case FIT_END:
                applyFitCenter();
                break;
            //$CASES-OMITTED$
            default:
                // Do nothing.
        }
    }

    return into(glide.buildImageViewTarget(view, transcodeClass));
}

最后实际调用到这个方法里面

public > Y into(Y target) {
    // 判断是否在主线程 ， 如果不在主线程那么就抛出异常    
    Util.assertMainThread();
    .....
    //获取之前的请求
    Request previous = target.getRequest();
    // requestTracker是请求跟踪类对象，主要管理请求的发起，暂停，清除 
    // 如果之前的请求已存在 ，那么就清空这个，并从 requestTracker 移除
    if (previous != null) {
        previous.clear();
        requestTracker.removeRequest(previous);
        previous.recycle();
    }
    //建立新的 请求
    Request request = buildRequest(target);
    // 设置 target 的request
    target.setRequest(request);
    //将target加入lifecycle
    lifecycle.addListener(target);
    //执行请求  
    requestTracker.runRequest(request);

    return target;
}

buildRequest 创建请求

先看看 创建请求 吧

private Request buildRequest(Target target) {
    if (priority == null) {
        priority = Priority.NORMAL;
    }
    return buildRequestRecursive(target, null);
}

private Request buildRequestRecursive(Target target, ThumbnailRequestCoordinator parentCoordinator) {
    if (thumbnailRequestBuilder != null) {

        ....
        // ①
        ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
        Request fullRequest = obtainRequest(target, sizeMultiplier, priority, coordinator);
        isThumbnailBuilt = true;
        Request thumbRequest = thumbnailRequestBuilder.buildRequestRecursive(target, coordinator);
        isThumbnailBuilt = false;
        coordinator.setRequests(fullRequest, thumbRequest);
        return coordinator;
    } else if (thumbSizeMultiplier != null) { // ②
        ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
        Request fullRequest = obtainRequest(target, sizeMultiplier, priority, coordinator);
        Request thumbnailRequest = obtainRequest(target, thumbSizeMultiplier, getThumbnailPriority(), coordinator);
        coordinator.setRequests(fullRequest, thumbnailRequest);
        return coordinator;
    } else { // ③
        return obtainRequest(target, sizeMultiplier, priority, parentCoordinator);
    }
}

根据 DrawableTypeRequest 的设置 ，如果对 DrawableTypeRequest 对象调用了 thumbnail 方法 ，那么就会执行 ① 或 ② ，否则执行 ③

   private Request obtainRequest(Target target, float sizeMultiplier, Priority priority,
        RequestCoordinator requestCoordinator) {
    return GenericRequest.obtain(
            loadProvider,
            model,
            signature,
            context,
            priority,
            target,
            sizeMultiplier,
            placeholderDrawable,
            placeholderId,
            errorPlaceholder,
            errorId,
            fallbackDrawable,
            fallbackResource,
            requestListener,
            requestCoordinator,
            glide.getEngine(),
            transformation,
            transcodeClass,
            isCacheable,
            animationFactory,
            overrideWidth,
            overrideHeight,
            diskCacheStrategy);
}

GenericRequest.java

public static  GenericRequest obtain(
        参数 ..... 
        DiskCacheStrategy diskCacheStrategy) {
    @SuppressWarnings("unchecked")
    GenericRequest request = (GenericRequest) REQUEST_POOL.poll();
    if (request == null) {
        request = new GenericRequest();
    }
    //初始化 request
    request.init(loadProvider,
            参数 ....
            diskCacheStrategy);
    return request;
}

runRequest 执行请求

public void runRequest(Request request) {
    //将request对象添加到请求集合中
    requests.add(request);
    //如果当前状态是非暂停的，调用begin方法发送请求
    if (!isPaused) {
        request.begin();
    } else {
        //将请求添加到挂起的请求集合
        pendingRequests.add(request);
    }
}

GenericRequest.java

@Override
public void begin() {
    startTime = LogTime.getLogTime();
    if (model == null) {
        // 加载错误
        onException(null);
        return;
    }

    status = Status.WAITING_FOR_SIZE;
    // 验证宽高是否合法
    if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
        // 注 1
        onSizeReady(overrideWidth, overrideHeight);
    } else {
        target.getSize(this);
    }
    //设置加载前的默认图片(placeholder)
    if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
        target.onLoadStarted(getPlaceholderDrawable());
    }
    ....
}

注 1

public void onSizeReady(int width, int height) {
    ....
    if (status != Status.WAITING_FOR_SIZE) {
        return;
    }
    // 将请求状态更新为运行状态
    status = Status.RUNNING;
    
    //根据 DrawableRequestBuilder 类的 sizeMultiplier 方法设置的  izeMultiplier 
    width = Math.round(sizeMultiplier * width);
    height = Math.round(sizeMultiplier * height);

    ....

    loadedFromMemoryCache = true;
    // 注 1
    loadStatus = engine.load(signature, width, height, dataFetcher, loadProvider, transformation, transcoder,
            priority, isMemoryCacheable, diskCacheStrategy, this);
    loadedFromMemoryCache = resource != null;
    ...
}

注 1 ： engine.load 这个 方法 就进入了图片的加载

public  LoadStatus load(Key signature, int width, int height, DataFetcher fetcher,
        DataLoadProvider loadProvider, Transformation transformation, ResourceTranscoder transcoder,
        Priority priority, boolean isMemoryCacheable, DiskCacheStrategy diskCacheStrategy, ResourceCallback cb) {
    // 判断是否在主线程
    Util.assertMainThread();
    long startTime = LogTime.getLogTime();

    final String id = fetcher.getId();
    // 创建 EngineKey 对象
    EngineKey key = keyFactory.buildKey(id, signature, width, height, loadProvider.getCacheDecoder(),
            loadProvider.getSourceDecoder(), transformation, loadProvider.getEncoder(),
            transcoder, loadProvider.getSourceEncoder());
    // 从内存缓存中查找
    EngineResource cached = loadFromCache(key, isMemoryCacheable);
    if (cached != null) {
        //缓存中存在，则回调 onResourceReady 
        cb.onResourceReady(cached);
        ...
        return null;
    }
    // 尝试从活动Resources 中获取，它表示的是当前正在使用的Resources，与内存缓存不同之处是clear缓存时不会clear它。
    EngineResource active = loadFromActiveResources(key, isMemoryCacheable);
    if (active != null) {
        //存在，则回调 onResourceReady 
        cb.onResourceReady(active);
        ...
        return null;
    }
    // 从 jobs 中获取是不是已经存在了这个任务，如果current != null ，那么之前已经提交了这个任务
    EngineJob current = jobs.get(key);
    if (current != null) {
        //为这个任务增加回调
        current.addCallback(cb);
        ....
        return new LoadStatus(cb, current);
    }
    // 缓存中没有，也没有提交过任务，那么就创建新的 EngineJob 
    EngineJob engineJob = engineJobFactory.build(key, isMemoryCacheable);
    DecodeJob decodeJob = new DecodeJob(key, width, height, fetcher, loadProvider, transformation,
            transcoder, diskCacheProvider, diskCacheStrategy, priority);
    //创建一个 EngineRunnable 。这个是任务执行的入口 ，实现了 Runnable 接口
    EngineRunnable runnable = new EngineRunnable(engineJob, decodeJob, priority);
    // 加入 jobs 
    jobs.put(key, engineJob);
    engineJob.addCallback(cb);
    //任务开始
    engineJob.start(runnable);

    .....
    return new LoadStatus(cb, engineJob);
}

任务 开始 ： engineJob.start(runnable);

public void start(EngineRunnable engineRunnable) {
    this.engineRunnable = engineRunnable;
    // diskCacheService 是线程池 ， 那么就把 runable 提交给线程池了
    future = diskCacheService.submit(engineRunnable);
}

那么就看看 engineRunnable 的 run 方法都实现了什么吧

@Override
public void run() {
    if (isCancelled) {
        return;
    }

    Exception exception = null;
    Resource resource = null;
    try {
        // 注 1
        resource = decode();
    } catch (Exception e) {
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            Log.v(TAG, "Exception decoding", e);
        }
        exception = e;
    }
    // 如果为取消，则回收各种资源
    if (isCancelled) {
        if (resource != null) {
            resource.recycle();
        }
        return;
    }

    if (resource == null) {
        // 加在失败
        onLoadFailed(exception);
    } else {
        // 加载成功
        onLoadComplete(resource);
    }
}

注 1

decode 方法就用来获取资源了

private Resource decode() throws Exception {
    if (isDecodingFromCache()) {
        // 从缓存中获取数据
        return decodeFromCache();
    } else {
        //从其他途径获取资源 (网络、file等)
        return decodeFromSource();
    }
}

decodeFromCache() 从缓存中获取数据

private Resource decodeFromCache() throws Exception {
    Resource result = null;
    try {
        result = decodeJob.decodeResultFromCache();
    } catch (Exception e) {
        ....
    }

    if (result == null) {
        result = decodeJob.decodeSourceFromCache();
    }
    return result;
}

那么就看看 decodeJob.decodeResultFromCache(); 里面干了什么

public Resource decodeResultFromCache() throws Exception {
    if (!diskCacheStrategy.cacheResult()) {
        return null;
    }

    long startTime = LogTime.getLogTime();
    //继续调用了 loadFromCache
    Resource transformed = loadFromCache(resultKey);
    ...
    startTime = LogTime.getLogTime();
    Resource result = transcode(transformed);
    ...
    return result;
}

private Resource loadFromCache(Key key) throws IOException {
    // 根据key从DiskCache获取文件
    File cacheFile = diskCacheProvider.getDiskCache().get(key);
    if (cacheFile == null) {
        return null;
    }

    Resource result = null;
    try {
        // 把缓存文件读取解码生成Resource
        result = loadProvider.getCacheDecoder().decode(cacheFile, width, height);
    } finally {
        if (result == null) {
            diskCacheProvider.getDiskCache().delete(key);
        }
    }
    return result;
}

decodeFromSource 从其他途径获取资源 (网络、file等)

private Resource decodeFromSource() throws Exception {
    //还是调用了decodeJob来获取与解码数据
    return decodeJob.decodeFromSource();
}

DecodeJob.java

public Resource decodeFromSource() throws Exception {
    Resource decoded = decodeSource();
    return transformEncodeAndTranscode(decoded);
}

private Resource decodeSource() throws Exception {
    Resource decoded = null;
    try {
        long startTime = LogTime.getLogTime();  
        // 注 1
        final A data = fetcher.loadData(priority);
        ....
        if (isCancelled) {
            return null;
        }
        decoded = decodeFromSourceData(data);
    } finally {
        fetcher.cleanup();
    }
    return decoded;
}

读取数据

fetcher.loadData(priority);

fetcher 是 DataFetcher 接口 ，实现 DataFetcher 的接口 就可以改变数据获取的方式(网络、文件) 或者 途径(OkHttp，Volley) 了 。我们以原有的 HttpUrlFetcher 来分析。

HttpUrlFetcher.java

@Override
public InputStream loadData(Priority priority) throws Exception {
    return loadDataWithRedirects(glideUrl.toURL(), 0 /*redirects*/, null /*lastUrl*/, glideUrl.getHeaders());
}

private InputStream loadDataWithRedirects(URL url, int redirects, URL lastUrl, Map headers)
        throws IOException {
    .....
    // 工厂创建 HttpURLConnection 对象
    urlConnection = connectionFactory.build(url);
    for (Map.Entry headerEntry : headers.entrySet()) {
      urlConnection.addRequestProperty(headerEntry.getKey(), headerEntry.getValue());
    }
    // 设置 网络连接参数
    urlConnection.setConnectTimeout(2500);
    urlConnection.setReadTimeout(2500);
    urlConnection.setUseCaches(false); // 不使用网络缓存
    urlConnection.setDoInput(true);

    urlConnection.connect();
    if (isCancelled) {
        return null;
    }
    final int statusCode = urlConnection.getResponseCode();
    if (statusCode / 100 == 2) {
        // 请求成功
        return getStreamForSuccessfulRequest(urlConnection);
    } else  {
        ...... 其他状态码判断
    }
}

gilde 的网络请求用到了 HttpURLConnection ，我么可以自定义 DataFetcher ，实现 DataFetcher 接口 ，从而使用其他库进行网络请求 ，如OkHttp，Volley。

加载完图片后自然就是进行缓存，留给下一次请求使用。省略缓存分析......

接下来就是回调显示

那么 回到 engineRunnable 里面的 run 方法

@Override
public void run() {
    ...
        resource = decode();
    ...
    if (resource == null) {
        onLoadFailed(exception);
    } else {
        onLoadComplete(resource);
    }
}

成功就调用 onLoadComplete ，失败就调用 onLoadFailed 。

private void onLoadComplete(Resource resource) {
    manager.onResourceReady(resource);
}

EngineJob.java

@Override
public void onResourceReady(final Resource resource) {
    this.resource = resource;
    MAIN_THREAD_HANDLER.obtainMessage(MSG_COMPLETE, this).sendToTarget();
}

上面会发送一条 Message ，随后的操作就会回到了主线程处理。

接受消息

private static class MainThreadCallback implements Handler.Callback {

    @Override
    public boolean handleMessage(Message message) {
        if (MSG_COMPLETE == message.what || MSG_EXCEPTION == message.what) {
            EngineJob job = (EngineJob) message.obj;
            if (MSG_COMPLETE == message.what) {
                job.handleResultOnMainThread();
            } else {
                job.handleExceptionOnMainThread();
            }
            return true;
        }

        return false;
    }
}


private void handleResultOnMainThread() {
    if (isCancelled) {
        resource.recycle();
        return;
    } else if (cbs.isEmpty()) {
        throw new IllegalStateException("Received a resource without any callbacks to notify");
    }
    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(key, engineResource);

    //注 1
    for (ResourceCallback cb : cbs) {
        if (!isInIgnoredCallbacks(cb)) {
            engineResource.acquire();
            cb.onResourceReady(engineResource);
        }
    }
    // Our request is complete, so we can release the resource.
    engineResource.release();
}

注 1 :

方法中通过一个循环，调用了所有ResourceCallback的 onResourceReady()方法。

而 onResourceReady() 方法最后的调用就会用于刷新相对应的UI。