Glide源码解析03-into

短命女 2023-10-17 13:07 64阅读 0赞

## Glide源码解析03-into\# ##

最简单的Glide调用，如下所示，下面将根据Glide的调用顺序，进行源码解析。

Glide.with(this)
            .load(uri)
            .into(img);

### into方法 ###

在上一步load方法中，我们初始化了一些数据，并返回了GenericRequestBuilder或其子类。现在，来看GenericRequestBuilder.into()

##### 3.0 GenericRequestBuilder\#into() #####

前面首先会判断当前线程，只有主线程才能继续执行。  
并且，如果没有设置过transform()或centerCrop，那么以ImageView的scaleType属性为准。

public Target<TranscodeType> into(ImageView view) {
        Util.assertMainThread(); //判断是否是主线程，如果不是会抛出异常。
        //...
    
    	//如果没有设置transform()或centerCrop()，那么以ImageView的scaleType属性为准
        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));
    }

##### 3.1 glide.buildImageViewTarget #####

来看Glide.buildImageViewTarget，在这个方法中会调用ImageViewTargetFactory\#buildTarget()

public <Z> Target<Z> buildTarget(ImageView view, Class<Z> clazz) {
        if (GlideDrawable.class.isAssignableFrom(clazz)) {
            return (Target<Z>) new GlideDrawableImageViewTarget(view);
        } else if (Bitmap.class.equals(clazz)) {
            return (Target<Z>) new BitmapImageViewTarget(view);
        } else if (Drawable.class.isAssignableFrom(clazz)) {
            return (Target<Z>) new DrawableImageViewTarget(view);
        } else {
            throw new IllegalArgumentException("Unhandled class: " + clazz
                    + ", try .as*(Class).transcode(ResourceTranscoder)");
        }
    }

这是个工厂方法，根据当前传入的clazz参数返回相应的类

1.  如果之前调用过asBitmap()方法，那么会返回BitmapImageViewTarget对象
2.  否则一般都是返回GlideDrawableImageViewTarget对象
3.  其他情况通常用不到

**注意这里**  
BitmapImageViewTarget和DrawableImageViewTarget就是具体是设置图片到ImageView的实现类，以DrawableImageViewTarget为例，可以看到`view.setImageDrawable(resource)`

public class DrawableImageViewTarget extends ImageViewTarget<Drawable> {
    
      public DrawableImageViewTarget(ImageView view) {
        super(view);
      }
    
      /**
       * @deprecated Use {@link #waitForLayout()} instead.
       */
      // Public API.
      @SuppressWarnings({"unused", "deprecation"})
      @Deprecated
      public DrawableImageViewTarget(ImageView view, boolean waitForLayout) {
        super(view, waitForLayout);
      }
    
      @Override
      protected void setResource(@Nullable Drawable resource) {
        view.setImageDrawable(resource);
      }
    }

回到1.0.0，我们再来看into方法

##### 3.2 GenericRequestBuilder\#into(Y target) #####

在这个方法中，主要会构建出一个Request对象，并执行这个Request对象。

public <Y extends Target<TranscodeType>> Y into(Y target) {
        Util.assertMainThread();
        //...
    
        Request previous = target.getRequest();
    
        if (previous != null) {
            previous.clear();
            requestTracker.removeRequest(previous);
            previous.recycle();
        }
    
    	//1.2.1 构建出了一个Request对象
        Request request = buildRequest(target);
        target.setRequest(request);
        lifecycle.addListener(target);
    	//1.2.3 执行这个request
        requestTracker.runRequest(request);
    
        return target;
    }

##### 3.3 buildRequest #####

先来看buildRequest，这里分成三种情况，但最终都会调用obtainRequest

private Request buildRequestRecursive(Target<TranscodeType> target, ThumbnailRequestCoordinator parentCoordinator) {
        if (thumbnailRequestBuilder != null) {
    		//设置过thumbnail(GenericRequestBuilder)或thumbnail(
            DrawableRequestBuilder)会调用这里
            //...
            Request fullRequest = obtainRequest(target, sizeMultiplier, priority, coordinator);
           	//...
            coordinator.setRequests(fullRequest, thumbRequest);
            return coordinator;
        } else if (thumbSizeMultiplier != null) {
    		//设置过 thumbnail(float)会调用这里
            //...
            Request thumbnailRequest = obtainRequest(target, thumbSizeMultiplier, getThumbnailPriority(), coordinator);
            coordinator.setRequests(fullRequest, thumbnailRequest);
            return coordinator;
        } else {
    		//没有设置过thumbnail(缩略图)会调用这里
            //...
            return obtainRequest(target, sizeMultiplier, priority, parentCoordinator);
        }
    }
    
    private Request obtainRequest(Target<TranscodeType> 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);
    }

##### 3.3.2 GenericRequestBuilder\#obtainRequest #####

来看obtainRequest，首先如果request没有初始化，则new GenericRequest对象。接着调用GenericRequest\#into方法 ，其内部是一些赋值的代码，将传入的这些参数赋值到GenericRequest的成员变量中。

public static <A, T, Z, R> GenericRequest<A, T, Z, R> obtain(...很多参数...) {
        //...
    	if (request == null) {
    		//创建GenericRequest对象
            request = new GenericRequest<A, T, Z, R>();
        }
    	//内部是一些赋值的代码，将传入的这些参数赋值到GenericRequest的成员变量当中
        request.init(loadProvider,
                model,
                signature,
                context,
                priority,
                target,
                sizeMultiplier,
                placeholderDrawable,
                placeholderResourceId,
                errorDrawable,
                errorResourceId,
                fallbackDrawable,
                fallbackResourceId,
                requestListener,
                requestCoordinator,
                engine,
                transformation,
                transcodeClass,
                isMemoryCacheable,
                animationFactory,
                overrideWidth,
                overrideHeight,
                diskCacheStrategy);
        return request;
    }

\#\#\#\#3.4 ReuqestTracker\#runRequest \#\#\#\#  
回到3.2，来看runRequest，这里是真正执行的地方。可以看到如果没有处于暂停状态，会直接调用request.begein()，如果处于暂停状态，那么先添加到队列中，等恢复到正常状态时，会再调用request.begin()。即无论如何都会调用request.begin()

public void runRequest(Request request) {
        requests.add(request);
        if (!isPaused) {
            request.begin();
        } else {
            pendingRequests.add(request);
        }
    }

##### 3.5 request\#begin() #####

那这个request到底是哪类类呢? 就是我们前面在 1.2.2 GenericRequestBuilder\#obtainRequest中分析的GenericRequest。  
在这里无论是onSizeReady还是target.getSize，最终都会调用onSizeReady。

@Override
    public void begin() {
    	//...
    	if (model == null) {
    		//model是存储url的，这里会调用setErrorPlaceholder，从而最终调用setImageDrawable
            onException(null);
            return;
    	}
        status = Status.WAITING_FOR_SIZE;
        if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
    		//使用了override() API指定了固定的宽高 调用这里
            onSizeReady(overrideWidth, overrideHeight);
        } else {
    		//没有使用了override() API指定固定的宽高 调用这里
    		//这个target.getSize()方法的内部会根据ImageView的layout_width和layout_height值做一系列的计算，来算出图片应该的宽高。
            target.getSize(this);
        }
    
        if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
            target.onLoadStarted(getPlaceholderDrawable());
        }
    	//...
    }

##### 3.6 onSizeReady #####

onSizeReady会确定图片的宽高并调用engine.load来执行加载。

public void onSizeReady(int width, int height) {
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logV("Got onSizeReady in " + LogTime.getElapsedMillis(startTime));
        }
        if (status != Status.WAITING_FOR_SIZE) {
            return;
        }
        status = Status.RUNNING;
    
        width = Math.round(sizeMultiplier * width);
        height = Math.round(sizeMultiplier * height);
    
    	//loadProvider内部封装了GifBitmapWrapperDrawableTranscoder、ImageVideoModelLoader、ImageVideoGifDrawableLoadProvider，
    	//这个对象是从load方法中构建出来的 -> 具体在DrawableTypeRequest构造方法中
    	//获取ImageVideoModelLoader
        ModelLoader<A, T> modelLoader = loadProvider.getModelLoader();
    	//获取ImageVideoFetcher
        final DataFetcher<T> dataFetcher = modelLoader.getResourceFetcher(model, width, height);
    
        if (dataFetcher == null) {
            onException(new Exception("Failed to load model: \'" + model + "\'"));
            return;
        }
    	//获取GifBitmapWrapperDrawableTranscoder
        ResourceTranscoder<Z, R> transcoder = loadProvider.getTranscoder();
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logV("finished setup for calling load in " + LogTime.getElapsedMillis(startTime));
        }
        loadedFromMemoryCache = true;
    	//[重点] 
        loadStatus = engine.load(signature, width, height, dataFetcher, loadProvider, transformation, transcoder,
                priority, isMemoryCacheable, diskCacheStrategy, this);
        loadedFromMemoryCache = resource != null;
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logV("finished onSizeReady in " + LogTime.getElapsedMillis(startTime));
        }
    }

##### 3.7 engine.load #####

这个方法中分为两步，第一步处理缓存，第二步真正执行加载，  
构建出EngineJob，并把callback (callback是GenericRequest对象)添加到EngineJob中，并且执行刚new出来的EngineRunnable

public <T, Z, R> LoadStatus load(Key signature, int width, int height, DataFetcher<T> fetcher,
            DataLoadProvider<T, Z> loadProvider, Transformation<Z> transformation, ResourceTranscoder<Z, R> transcoder,
            Priority priority, boolean isMemoryCacheable, DiskCacheStrategy diskCacheStrategy, ResourceCallback cb) {
    
    	//处理缓存
        final String id = fetcher.getId();
        EngineKey key = keyFactory.buildKey(id, signature, width, height, loadProvider.getCacheDecoder(),
                loadProvider.getSourceDecoder(), transformation, loadProvider.getEncoder(),
                transcoder, loadProvider.getSourceEncoder());
    
        EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
        if (cached != null) {
            cb.onResourceReady(cached);
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                logWithTimeAndKey("Loaded resource from cache", startTime, key);
            }
            return null;
        }
    
        EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
        if (active != null) {
            cb.onResourceReady(active);
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                logWithTimeAndKey("Loaded resource from active resources", startTime, key);
            }
            return null;
        }
    
        EngineJob current = jobs.get(key);
        if (current != null) {
            current.addCallback(cb);
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                logWithTimeAndKey("Added to existing load", startTime, key);
            }
            return new LoadStatus(cb, current);
        }
    
        EngineJob engineJob = engineJobFactory.build(key, isMemoryCacheable);
        DecodeJob<T, Z, R> decodeJob = new DecodeJob<T, Z, R>(key, width, height, fetcher, loadProvider, transformation,
                transcoder, diskCacheProvider, diskCacheStrategy, priority);
        EngineRunnable runnable = new EngineRunnable(engineJob, decodeJob, priority);
        jobs.put(key, engineJob);
        engineJob.addCallback(cb);
    	//真正执行
        engineJob.start(runnable);
    
       	//...
        return new LoadStatus(cb, engineJob);
    }

##### 3.8 EngineRunnable\#run() #####

engineJob.start()会执行EngineRunnable的run方法。

public void run() {
        if (isCancelled) {
            return;
        }
    
        Exception exception = null;
        Resource<?> resource = null;
        try {
    		//1.3.0 解码
            resource = decode();
        } catch (Exception e) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "Exception decoding", e);
            }
            exception = e;
        }
    
        if (isCancelled) {
            if (resource != null) {
                resource.recycle();
            }
            return;
        }
    
    	//1.3.2 加载结果
        if (resource == null) {
            onLoadFailed(exception);
        } else {
            onLoadComplete(resource);
        }
    }

##### 3.9 decode #####

decode方法进行了解码，返回Resource对象，详情看[ Glide源码解析04-decode][Glide_04-decode]

##### 3.10 onLoadFailed or onLoadComplete #####

如果resource为null，则执行加载失败的逻辑，如果不为null，则执行加载成功的逻辑。详情看[Glide源码解析05-onLoadComplete][Glide_05-onLoadComplete]

\#\#\#更多  
[Glide源码解析01-with][Glide_01-with]  
[Glide源码解析02-load][Glide_02-load]  
[Glide源码解析03-into][Glide_03-into]  
[ Glide源码解析04-decode][Glide_04-decode]  
[Glide源码解析05-onLoadComplete][Glide_05-onLoadComplete]  
[Glide源码解析06-Glide流程图][Glide_06-Glide]

[Glide_04-decode]: http://blog.csdn.net/ethanco/article/details/72085588
[Glide_05-onLoadComplete]: http://blog.csdn.net/ethanco/article/details/72085605
[Glide_01-with]: http://blog.csdn.net/ethanco/article/details/71977252
[Glide_02-load]: http://blog.csdn.net/ethanco/article/details/71983310
[Glide_03-into]: http://blog.csdn.net/ethanco/article/details/72085582
[Glide_06-Glide]: http://blog.csdn.net/ethanco/article/details/72085606