Glide的基本用法

 ImageView imageView = findViewById(R.id.test);
 Glide.with(getApplicationContext())
            .load(imageUrl)
            .into(imageView);

基于Glide 3.5.2
先看with方法做了什么

// 一組靜態(tài)方法 有好幾個(gè)重載方法 選取其中一個(gè)分析
public static RequestManager with(Context context) {
        RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(context);
    }

RequestManagerRetriever.get()獲取單例
RequestManagerRetriever的邏輯很簡(jiǎn)單怜械，會(huì)根據(jù)我們傳入with()方法的參數(shù)來(lái)確定圖片加載的生命周期滤港，是activity和fragment 則添加一個(gè)隱藏的fragment耀盗，響應(yīng)activity，fragment 的生命周期仔沿，請(qǐng)他情況就是使用ApplicationContext作為生命周期,然后返回RequestManager。
然后接著分析load方法

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

public DrawableTypeRequest<String> fromString() {
        return loadGeneric(String.class);
    }

private <T> DrawableTypeRequest<T> loadGeneric(Class<T> modelClass) {
        ModelLoader<T, InputStream> streamModelLoader = Glide.buildStreamModelLoader(modelClass, context);
        ModelLoader<T, ParcelFileDescriptor> fileDescriptorModelLoader =
                Glide.buildFileDescriptorModelLoader(modelClass, context);
        if (modelClass != null && streamModelLoader == null && fileDescriptorModelLoader == null) {
            throw new IllegalArgumentException("Unknown type " + modelClass + ". You must provide a Model of a type for"
                    + " which there is a registered ModelLoader, if you are using a custom model, you must first call"
                    + " Glide#register with a ModelLoaderFactory for your custom model class");
        }

        return optionsApplier.apply(
                new DrawableTypeRequest<T>(modelClass, streamModelLoader, fileDescriptorModelLoader, context,
                        glide, requestTracker, lifecycle, optionsApplier));
    }

在loadGeneric 分別調(diào)用了Glide.buildStreamModelLoader()方法和Glide.buildFileDescriptorModelLoader()方法來(lái)獲得ModelLoader對(duì)象滞磺。ModelLoader對(duì)象是用于加載圖片的异旧，而我們給load()方法傳入不同類型的參數(shù)，這里也會(huì)得到不同的ModelLoader對(duì)象佣谐。由于我們剛才傳入的參數(shù)是String.class肚吏，因此最終得到的是StreamStringLoader對(duì)象，它是實(shí)現(xiàn)了ModelLoader接口的狭魂，最后返回DrawableTypeRequest對(duì)象罚攀，然后調(diào)用父類的 load(ModelType model)方法

public GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> load(ModelType model) {
        this.model = model;
        isModelSet = true;
        return this;
    }

還是返回的DrawableTypeRequest對(duì)象党觅，接著看into方法。

 public Target<TranscodeType> 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.
            }
        }
        // 創(chuàng)建一個(gè)target
        return into(glide.buildImageViewTarget(view, transcodeClass));
    }

glide.buildImageViewTarget(view, transcodeClass) 根據(jù)不同的類型創(chuàng)建不同target斋泄，GlideDrawableImageViewTarget,BitmapImageViewTarget,DrawableImageViewTarget三個(gè)杯瞻。然后繼續(xù)里面的into方法,傳入target。

 public <Y extends Target<TranscodeType>> Y into(Y target) {
        Util.assertMainThread();
        if (target == null) {
            throw new IllegalArgumentException("You must pass in a non null Target");
        }
        if (!isModelSet) {
            throw new IllegalArgumentException("You must first set a model (try #load())");
        }
        Request previous = target.getRequest();

        if (previous != null) {
            previous.clear();
            requestTracker.removeRequest(previous);
            previous.recycle();
        }
          // 網(wǎng)絡(luò)請(qǐng)求圖片
        Request request = buildRequest(target);
        target.setRequest(request);
        lifecycle.addListener(target);
        requestTracker.runRequest(request);

        return target;
    }

最為關(guān)鍵的是buildRequest方法最后返回的對(duì)象

    public static <A, T, Z, R> GenericRequest<A, T, Z, R> obtain(
            LoadProvider<A, T, Z, R> loadProvider,
            A model,
            Key signature,
            Context context,
            Priority priority,
            Target<R> target,
            float sizeMultiplier,
            Drawable placeholderDrawable,
            int placeholderResourceId,
            Drawable errorDrawable,
            int errorResourceId,
            RequestListener<? super A, R> requestListener,
            RequestCoordinator requestCoordinator,
            Engine engine,
            Transformation<Z> transformation,
            Class<R> transcodeClass,
            boolean isMemoryCacheable,
            GlideAnimationFactory<R> animationFactory,
            int overrideWidth,
            int overrideHeight,
            DiskCacheStrategy diskCacheStrategy) {
        @SuppressWarnings("unchecked")
        GenericRequest<A, T, Z, R> request = (GenericRequest<A, T, Z, R>) REQUEST_POOL.poll();
        if (request == null) {
            request = new GenericRequest<A, T, Z, R>();
        }
        request.init(loadProvider,
                model,
                signature,
                context,
                priority,
                target,
                sizeMultiplier,
                placeholderDrawable,
                placeholderResourceId,
                errorDrawable,
                errorResourceId,
                requestListener,
                requestCoordinator,
                engine,
                transformation,
                transcodeClass,
                isMemoryCacheable,
                animationFactory,
                overrideWidth,
                overrideHeight,
                diskCacheStrategy);
        return request;
    }

通過(guò)request.init方法初始化炫掐，返回一個(gè) GenericRequest對(duì)象,然后接著看run方法魁莉。

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

當(dāng)在沒(méi)有暫停的情況下會(huì)執(zhí)行begin方法

    public void begin() {
        startTime = LogTime.getLogTime();
        if (model == null) {
           // 設(shè)置出錯(cuò)時(shí)顯示的圖片
            onException(null);
            return;
        }

        status = Status.WAITING_FOR_SIZE;
        if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
            onSizeReady(overrideWidth, overrideHeight);
        } else {
            target.getSize(this);
        }

        if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
            // 獲取loading圖片設(shè)置
            target.onLoadStarted(getPlaceholderDrawable());
        }
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logV("finished run method in " + LogTime.getElapsedMillis(startTime));
        }
    }

onSizeReady(overrideWidth, overrideHeight);算出原圖尺寸后開始調(diào)用這個(gè)方法。

 @Override
    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); 
        ModelLoader<A, T> modelLoader = loadProvider.getModelLoader();
        final DataFetcher<T> dataFetcher = modelLoader.getResourceFetcher(model, width, height);

        if (dataFetcher == null) {
            onException(new Exception("Got null fetcher from model loader"));
            return;
        }
        ResourceTranscoder<Z, R> transcoder = loadProvider.getTranscoder();
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logV("finished setup for calling load in " + LogTime.getElapsedMillis(startTime));
        }
        loadedFromMemoryCache = true;
        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));
        }
    } 

engine.load(signature, width, height, dataFetcher, loadProvider, transformation, transcoder, priority, isMemoryCacheable, diskCacheStrategy, this);是該方法最重要的方法募胃。

 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) {
        Util.assertMainThread();
        long startTime = LogTime.getLogTime();

        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) {
            // 內(nèi)存緩存- LruCache緩存
            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) {
             // 內(nèi)存緩存- 弱引用
            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);
        engineJob.start(runnable);

        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logWithTimeAndKey("Started new load", startTime, key);
        }
        return new LoadStatus(cb, engineJob);
    }

load()方法中的代碼有點(diǎn)長(zhǎng)旗唁，基本都是在處理緩存的。最重要的是調(diào)用了EngineJob的start()方法來(lái)運(yùn)行EngineRunnable對(duì)象摔认，讓EngineRunnable的run()方法在子線程當(dāng)中執(zhí)行了逆皮。那么我們現(xiàn)在就可以去看看EngineRunnable的run()方法里做了什么？

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

        Exception exception = null;
        Resource<?> resource = null;
        try {
            // 在這進(jìn)行圖片解碼
            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;
        }

        if (resource == null) {
            onLoadFailed(exception);
        } else {
            onLoadComplete(resource);
        }
    }

decode方法 完成圖片從遠(yuǎn)程到resource的轉(zhuǎn)變参袱。

 private Resource<?> decode() throws Exception {
        if (isDecodingFromCache()) {
            // 文件緩存
            return decodeFromCache();
        } else {
            // 網(wǎng)絡(luò)請(qǐng)求
            return decodeFromSource();
        }
    }

按照有無(wú)緩存分為兩種情況电谣，暫時(shí)不研究緩存是怎么實(shí)現(xiàn)的。

private Resource<T> decodeSource() throws Exception {
        Resource<T> decoded = null;
        try {
            long startTime = LogTime.getLogTime();
            final A data = fetcher.loadData(priority);
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                logWithTimeAndKey("Fetched data", startTime);
            }
            if (isCancelled) {
                return null;
            }
            decoded = decodeFromSourceData(data);
        } finally {
            fetcher.cleanup();
        }
        return decoded;
    }

loadData做了請(qǐng)求數(shù)據(jù)的事情抹蚀，fetcher是HttpUrlFetcher的對(duì)象
看下loadData最后調(diào)用的方法

private InputStream loadDataWithRedirects(URL url, int redirects, URL lastUrl) throws IOException {
        if (redirects >= MAXIMUM_REDIRECTS) {
            throw new IOException("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 IOException("In re-direct loop");
                }
            } catch (URISyntaxException e) {
                // Do nothing, this is best effort.
            }
        }
       // 這一段很熟悉 利用HttpUrlConnection進(jìn)行了網(wǎng)絡(luò)請(qǐng)求 設(shè)置請(qǐng)求參數(shù)
        urlConnection = connectionFactory.build(url);
        urlConnection.setConnectTimeout(2500);
        urlConnection.setReadTimeout(2500);
        urlConnection.setUseCaches(false);
        urlConnection.setDoInput(true);

        // Connect explicitly to avoid errors in decoders if connection fails.
        urlConnection.connect();
        if (isCancelled) {
            return null;
        }
        final int statusCode = urlConnection.getResponseCode();
        if (statusCode / 100 == 2) {
            stream = urlConnection.getInputStream();
            return stream;
        } else if (statusCode / 100 == 3) {
            String redirectUrlString = urlConnection.getHeaderField("Location");
            if (TextUtils.isEmpty(redirectUrlString)) {
                throw new IOException("Received empty or null redirect url");
            }
            URL redirectUrl = new URL(url, redirectUrlString);
            return loadDataWithRedirects(redirectUrl, redirects + 1, url);
        } else {
            if (statusCode == -1) {
                throw new IOException("Unable to retrieve response code from HttpUrlConnection.");
            }
            throw new IOException("Request failed " + statusCode + ": " + urlConnection.getResponseMessage());
        }
    }

但是還沒(méi)有完 這只是返回一個(gè)InputStream剿牺，獲得輸入流后返回繼續(xù)往下走，decodeFromSourceData(data)的decode方法

 public Resource<Bitmap> decode(ImageVideoWrapper source, int width, int height) throws IOException {
        Resource<Bitmap> result = null;
        InputStream is = source.getStream();
        if (is != null) {
            try {
                // 調(diào)用的是 StreamBitmapDecoder的decode方法
                result = streamDecoder.decode(is, width, height);
            } catch (IOException e) {
                if (Log.isLoggable(TAG, Log.VERBOSE)) {
                    Log.v(TAG, "Failed to load image from stream, trying FileDescriptor", e);
                }
            }
        }
        if (result == null) {
            ParcelFileDescriptor fileDescriptor = source.getFileDescriptor();
            if (fileDescriptor != null) {
                result = fileDescriptorDecoder.decode(fileDescriptor, width, height);
            }
        }
        return result;
    }

StreamBitmapDecoder的decode方法

 public Resource<Bitmap> decode(InputStream source, int width, int height) {
         // Downsampler的 decode
        Bitmap bitmap = this.downsampler.decode(source, this.bitmapPool, width, height, this.decodeFormat);
        return BitmapResource.obtain(bitmap, this.bitmapPool);
    }

看下Downsampler的 decode 終于返回了bitmap對(duì)象

 @Override
    public Bitmap decode(InputStream is, BitmapPool pool, int outWidth, int outHeight, DecodeFormat decodeFormat) {
        final ByteArrayPool byteArrayPool = ByteArrayPool.get();
        final byte[] bytesForOptions = byteArrayPool.getBytes();
        final byte[] bytesForStream = byteArrayPool.getBytes();
        final BitmapFactory.Options options = getDefaultOptions();

        // Use to fix the mark limit to avoid allocating buffers that fit entire images.
        RecyclableBufferedInputStream bufferedStream = new RecyclableBufferedInputStream(
                is, bytesForStream);
        // Use to retrieve exceptions thrown while reading.
        // TODO(#126): when the framework no longer returns partially decoded Bitmaps or provides a way to determine
        // if a Bitmap is partially decoded, consider removing.
        ExceptionCatchingInputStream exceptionStream =
                ExceptionCatchingInputStream.obtain(bufferedStream);
        // Use to read data.
        // Ensures that we can always reset after reading an image header so that we can still attempt to decode the
        // full image even when the header decode fails and/or overflows our read buffer. See #283.
        MarkEnforcingInputStream invalidatingStream = new MarkEnforcingInputStream(exceptionStream);
        try {
            exceptionStream.mark(MARK_POSITION);
            int orientation = 0;
            try {
                orientation = new ImageHeaderParser(exceptionStream).getOrientation();
            } catch (IOException e) {
                if (Log.isLoggable(TAG, Log.WARN)) {
                    Log.w(TAG, "Cannot determine the image orientation from header", e);
                }
            } finally {
                try {
                    exceptionStream.reset();
                } catch (IOException e) {
                    if (Log.isLoggable(TAG, Log.WARN)) {
                        Log.w(TAG, "Cannot reset the input stream", e);
                    }
                }
            }

            options.inTempStorage = bytesForOptions;

            final int[] inDimens = getDimensions(invalidatingStream, bufferedStream, options);
            final int inWidth = inDimens[0];
            final int inHeight = inDimens[1];

            final int degreesToRotate = TransformationUtils.getExifOrientationDegrees(orientation);
            final int sampleSize = getRoundedSampleSize(degreesToRotate, inWidth, inHeight, outWidth, outHeight);

            final Bitmap downsampled =
                    downsampleWithSize(invalidatingStream, bufferedStream, options, pool, inWidth, inHeight, sampleSize,
                            decodeFormat);

            // BitmapFactory swallows exceptions during decodes and in some cases when inBitmap is non null, may catch
            // and log a stack trace but still return a non null bitmap. To avoid displaying partially decoded bitmaps,
            // we catch exceptions reading from the stream in our ExceptionCatchingInputStream and throw them here.
            final Exception streamException = exceptionStream.getException();
            if (streamException != null) {
                throw new RuntimeException(streamException);
            }

            Bitmap rotated = null;
            if (downsampled != null) {
                rotated = TransformationUtils.rotateImageExif(downsampled, pool, orientation);

                if (!downsampled.equals(rotated) && !pool.put(downsampled)) {
                    downsampled.recycle();
                }
            }

            return rotated;
        } finally {
            byteArrayPool.releaseBytes(bytesForOptions);
            byteArrayPool.releaseBytes(bytesForStream);
            exceptionStream.release();
            releaseOptions(options);
        }
    }

這個(gè)方法做了很多操作环壤，圖片壓縮晒来，圓角處理等邏輯。
最后通過(guò)downsampleWithSize-> final Bitmap result = BitmapFactory.decodeStream(is, null, options);獲取到了Bitmap郑现。
接下來(lái)就是對(duì)于Bitmap的顯示設(shè)置了湃崩。往上翻代碼會(huì)執(zhí)行onLoadComplete(resource);

 private void onLoadComplete(Resource resource) {
        manager.onResourceReady(resource);
    }
 @Override
    public void onResourceReady(final Resource<?> resource) {
        this.resource = resource;
        MAIN_THREAD_HANDLER.obtainMessage(MSG_COMPLETE, this).sendToTarget();
    }
// 這邊回到主線程進(jìn)行UI操作
 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;
        }`
    }
// handleResultOnMainThread
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);

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

又回到GenericRequest 的onResourceReady

public void onResourceReady(Resource<?> resource) {
        if (resource == null) {
            onException(new Exception("Expected to receive a Resource<R> with an object of " + transcodeClass
                    + " inside, but instead got null."));
            return;
        }

        Object received = resource.get();
        if (received == null || !transcodeClass.isAssignableFrom(received.getClass())) {
            releaseResource(resource);
            onException(new Exception("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.")
            ));
            return;
        }

        if (!canSetResource()) {
            releaseResource(resource);
            // We can't set the status to complete before asking canSetResource().
            status = Status.COMPLETE;
            return;
        }

        onResourceReady(resource, (R) received);
    }

onResourceReady(resource, (R) received); 又到了GlideDrawableImageViewTarget的onResourceReady

@Override
    public void onResourceReady(GlideDrawable resource, GlideAnimation<? super GlideDrawable> animation) {
        if (!resource.isAnimated()) {
            float viewRatio = view.getWidth() / (float) view.getHeight();
            float drawableRatio = resource.getIntrinsicWidth() / (float) resource.getIntrinsicHeight();
            if (Math.abs(viewRatio - 1f) <= SQUARE_RATIO_MARGIN
                    && Math.abs(drawableRatio - 1f) <= SQUARE_RATIO_MARGIN) {
                resource = new SquaringDrawable(resource, view.getWidth());
            }
        }
        // 父類調(diào)用setResource設(shè)置
        super.onResourceReady(resource, animation);
        this.resource = resource;
        resource.setLoopCount(maxLoopCount);
        resource.start();
    }

    @Override
    protected void setResource(GlideDrawable resource) {
        view.setImageDrawable(resource);
    }

到這里 這個(gè)最簡(jiǎn)單的流程就走完了

Glide.with(this).load(url).into(imageView);

代碼多的嚇人 - -