看了一些Glide源码分析的文章，发觉里面的部分代码实现已经发生变化，而对一些要点也没有深入分析，于是姑且自己总结一下。
※基于Glide 3.7.0。
Glide的简单使用例子：
// For a simple view:
@Override public void onCreate(Bundle savedInstanceState) {
...
ImageView imageView = (ImageView) findViewById(R.id.my_image_view);
Glide.with(this).load("http://goo.gl/gEgYUd").into(imageView);
}
先看Glide的with方法。
//com.bumptech.glide.Glide:
/**
* Begin a load with Glide by passing in a context.
*
* <p>
* Any requests started using a context will only have the application level options applied and will not be
* started or stopped based on lifecycle events. In general, loads should be started at the level the result
* will be used in. If the resource will be used in a view in a child fragment,
* the load should be started with {@link #with(android.app.Fragment)}} using that child fragment. Similarly,
* if the resource will be used in a view in the parent fragment, the load should be started with
* {@link #with(android.app.Fragment)} using the parent fragment. In the same vein, if the resource will be used
* in a view in an activity, the load should be started with {@link #with(android.app.Activity)}}.
* </p>
*
* <p>
* This method is appropriate for resources that will be used outside of the normal fragment or activity
* lifecycle (For example in services, or for notification thumbnails).
* </p>
*
* @see #with(android.app.Activity)
* @see #with(android.app.Fragment)
* @see #with(android.support.v4.app.Fragment)
* @see #with(android.support.v4.app.FragmentActivity)
*
* @param context Any context, will not be retained.
* @return A RequestManager for the top level application that can be used to start a load.
*/
public static RequestManager with(Context context) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(context);
}
with方法传入的参数可以是Context，Activity，Fragment或FragmentActiviy，这里以Context为例。
//com.bumptech.glide.manager.RequestManagerRetriever:
private RequestManager getApplicationManager(Context context) {
// Either an application context or we're on a background thread.
if (applicationManager == null) {
synchronized (this) {
if (applicationManager == null) {
// Normally pause/resume is taken care of by the fragment we add to the fragment or activity.
// However, in this case since the manager attached to the application will not receive lifecycle
// events, we must force the manager to start resumed using ApplicationLifecycle.
applicationManager = new RequestManager(context.getApplicationContext(),
new ApplicationLifecycle(), new EmptyRequestManagerTreeNode());
}
}
}
return applicationManager;
}
public RequestManager get(Context context) {
if (context == null) {
throw new IllegalArgumentException("You cannot start a load on a null Context");
} else if (Util.isOnMainThread() && !(context instanceof Application)) {
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());
}
}
return getApplicationManager(context);
}
public RequestManager get(FragmentActivity activity) {
if (Util.isOnBackgroundThread()) {
return get(activity.getApplicationContext());
} else {
assertNotDestroyed(activity);
FragmentManager fm = activity.getSupportFragmentManager();
return supportFragmentGet(activity, fm);
}
}
RequestManager supportFragmentGet(Context context, FragmentManager fm) {
SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
current.setRequestManager(requestManager);
}
return requestManager;
}
SupportRequestManagerFragment getSupportRequestManagerFragment(final FragmentManager fm) {
SupportRequestManagerFragment current = (SupportRequestManagerFragment) fm.findFragmentByTag(
FRAGMENT_TAG);
if (current == null) {
current = pendingSupportRequestManagerFragments.get(fm);
if (current == null) {
current = new SupportRequestManagerFragment();
pendingSupportRequestManagerFragments.put(fm, current);
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
}
}
return current;
}
根据传入Context的类型有不同的实现，这里以FragmentActivity为例（现在常用的MD样式Activity类AppCompatActivity是FragmentActivity的子类）。方法get(FragmentActivity activity)调用了方法supportFragmentGet(activity, fm)，后者返回的对象类型是SupportRequestManagerFragment 。SupportRequestManagerFragment 是一个无界面的Fragment类，起到把请求和Activity生命周期同步的作用。
然后看加载的发起点into方法。
//com.bumptech.glide.DrawableRequestBuilder:
@Override
public Target<GlideDrawable> into(ImageView view) {
return super.into(view);
}
//com.bumptech.glide.GenericRequestBuilder:
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.
}
}
return into(glide.buildImageViewTarget(view, transcodeClass));
}
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();
}
Request request = buildRequest(target);
target.setRequest(request);
lifecycle.addListener(target);
requestTracker.runRequest(request);
return target;
}
//com.bumptech.glide.manager.RequestTracker
/**
* Starts tracking the given request.
*/
public void runRequest(Request request) {
requests.add(request);
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
//com.bumptech.glide.request.GenericRequest:
@Override
public void begin() {
startTime = LogTime.getLogTime();
if (model == null) {
onException(null);
return;
}
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
}
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
}
}
/**
* A callback method that should never be invoked directly.
*/
@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("Failed to load model: \'" + model + "\'"));
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));
}
}
onSizeReady方法中调用了Engine的load方法。
//com.bumptech.glide.load.engine.Engine:
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) {
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);
engineJob.start(runnable);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Started new load", startTime, key);
}
return new LoadStatus(cb, engineJob);
}
private EngineResource<?> loadFromActiveResources(Key key, boolean isMemoryCacheable) {
if (!isMemoryCacheable) {
return null;
}
EngineResource<?> active = null;
WeakReference<EngineResource<?>> activeRef = activeResources.get(key);
if (activeRef != null) {
active = activeRef.get();
if (active != null) {
active.acquire();
} else {
activeResources.remove(key);
}
}
return active;
}
private EngineResource<?> loadFromCache(Key key, boolean isMemoryCacheable) {
if (!isMemoryCacheable) {
return null;
}
EngineResource<?> cached = getEngineResourceFromCache(key);
if (cached != null) {
cached.acquire();
activeResources.put(key, new ResourceWeakReference(key, cached, getReferenceQueue()));
}
return cached;
}
private EngineResource<?> getEngineResourceFromCache(Key key) {
Resource<?> cached = cache.remove(key);
final EngineResource result;
if (cached == null) {
result = null;
} else if (cached instanceof EngineResource) {
// Save an object allocation if we've cached an EngineResource (the typical case).
result = (EngineResource) cached;
} else {
result = new EngineResource(cached, true /*isCacheable*/);
}
return result;
}
先从cache中寻找资源，如果找到则将其从cache中移除并放入activeResources中，否则从activeResources中寻找。cache是LruResourceCache对象，作为资源的LRU缓存；activeResources是以弱引用为值的Map，用于缓存使用中的资源。比一般内存缓存额外多一级缓存的意义在于，当内存不足时清理cache中的资源时，不会对使用中的Bitmap造成影响。
若再次寻找失败，则创建EngineJob对象并调用其start方法。
//com.bumptech.glide.load.engine.EngineJob
public void start(EngineRunnable engineRunnable) {
this.engineRunnable = engineRunnable;
future = diskCacheService.submit(engineRunnable);
}
diskCacheService的类型是ThreadPoolExecutor的子类FifoPriorityThreadPoolExecutor，也就是说将engineRunnable放入线程池中执行。
//com.bumptech.glide.load.engine.EngineRunnable:
@Override
public void run() {
if (isCancelled) {
return;
}
Exception exception = null;
Resource<?> resource = null;
try {
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);
}
}
private Resource<?> decode() throws Exception {
if (isDecodingFromCache()) {
return decodeFromCache();
} else {
return decodeFromSource();
}
}
private Resource<?> decodeFromSource() throws Exception {
return decodeJob.decodeFromSource();
}
在EngineRunnable的run方法中进行编码，根据缓存策略调用decodeFromCache或者decodeFromSource。
先看decodeFromSource，调用DecodeJob的decodeFromSource方法。
//com.bumptech.glide.load.engine.DecodeJob:
/**
* Returns a transformed and transcoded resource decoded from source data, or null if no source data could be
* obtained or no resource could be decoded.
*
* <p>
* Depending on the {@link com.bumptech.glide.load.engine.DiskCacheStrategy} used, source data is either decoded
* directly or first written to the disk cache and then decoded from the disk cache.
* </p>
*
* @throws Exception
*/
public Resource<Z> decodeFromSource() throws Exception {
Resource<T> decoded = decodeSource();
return transformEncodeAndTranscode(decoded);
}
private Resource<Z> transformEncodeAndTranscode(Resource<T> decoded) {
long startTime = LogTime.getLogTime();
Resource<T> transformed = transform(decoded);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Transformed resource from source", startTime);
}
writeTransformedToCache(transformed);
startTime = LogTime.getLogTime();
Resource<Z> result = transcode(transformed);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Transcoded transformed from source", startTime);
}
return result;
}
private Resource<T> transform(Resource<T> decoded) {
if (decoded == null) {
return null;
}
Resource<T> transformed = transformation.transform(decoded, width, height);
if (!decoded.equals(transformed)) {
decoded.recycle();
}
return transformed;
}
private Resource<Z> transcode(Resource<T> transformed) {
if (transformed == null) {
return null;
}
return transcoder.transcode(transformed);
}
private void writeTransformedToCache(Resource<T> transformed) {
if (transformed == null || !diskCacheStrategy.cacheResult()) {
return;
}
long startTime = LogTime.getLogTime();
SourceWriter<Resource<T>> writer = new SourceWriter<Resource<T>>(loadProvider.getEncoder(), transformed);
diskCacheProvider.getDiskCache().put(resultKey, writer);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Wrote transformed from source to cache", startTime);
}
}
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;
}
private Resource<T> decodeFromSourceData(A data) throws IOException {
final Resource<T> decoded;
if (diskCacheStrategy.cacheSource()) {
decoded = cacheAndDecodeSourceData(data);
} else {
long startTime = LogTime.getLogTime();
decoded = loadProvider.getSourceDecoder().decode(data, width, height);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Decoded from source", startTime);
}
}
return decoded;
}
private Resource<T> cacheAndDecodeSourceData(A data) throws IOException {
long startTime = LogTime.getLogTime();
SourceWriter<A> writer = new SourceWriter<A>(loadProvider.getSourceEncoder(), data);
diskCacheProvider.getDiskCache().put(resultKey.getOriginalKey(), writer);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Wrote source to cache", startTime);
}
startTime = LogTime.getLogTime();
Resource<T> result = loadFromCache(resultKey.getOriginalKey());
if (Log.isLoggable(TAG, Log.VERBOSE) && result != null) {
logWithTimeAndKey("Decoded source from cache", startTime);
}
return result;
}
private Resource<T> loadFromCache(Key key) throws IOException {
File cacheFile = diskCacheProvider.getDiskCache().get(key);
if (cacheFile == null) {
return null;
}
Resource<T> result = null;
try {
result = loadProvider.getCacheDecoder().decode(cacheFile, width, height);
} finally {
if (result == null) {
diskCacheProvider.getDiskCache().delete(key);
}
}
return result;
}
编码前需要先通过DataFetcher访问网络获得文件流。接口DataFetcher的实现类根据配置而不同，设置为通过OkHttp3进行网络通信的情况下，该实现类为OkHttpStreamFetcher。
之后根据需要将文件流写入磁盘缓存，再对文件流进行编码。
//com.bumptech.glide.load.resource.bitmap.StreamBitmapDecoder:
@Override
public Resource<Bitmap> decode(InputStream source, int width, int height) {
Bitmap bitmap = downsampler.decode(source, bitmapPool, width, height, decodeFormat);
return BitmapResource.obtain(bitmap, bitmapPool);
}
//com.bumptech.glide.load.resource.bitmap.Downsampler:
@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);
}
}
编码过程中通过设置采样率缩放图片，降低内存占用，提高加载性能。
编码之后通过transformEncodeAndTranscode方法进行转换处理。transform方法调用了Transformation的transform方法。Transformation是接口；BitmapTransformation实现了该接口但留下了另一个抽象方法transform；CenterCrop和FitCenter两个类继承了BitmapTransformation并实现了抽象方法transform。
//com.bumptech.glide.load.resource.bitmap.BitmapTransformation:
@Override
public final Resource<Bitmap> transform(Resource<Bitmap> resource, int outWidth, int outHeight) {
if (!Util.isValidDimensions(outWidth, outHeight)) {
throw new IllegalArgumentException("Cannot apply transformation on width: " + outWidth + " or height: "
+ outHeight + " less than or equal to zero and not Target.SIZE_ORIGINAL");
}
Bitmap toTransform = resource.get();
int targetWidth = outWidth == Target.SIZE_ORIGINAL ? toTransform.getWidth() : outWidth;
int targetHeight = outHeight == Target.SIZE_ORIGINAL ? toTransform.getHeight() : outHeight;
Bitmap transformed = transform(bitmapPool, toTransform, targetWidth, targetHeight);
final Resource<Bitmap> result;
if (toTransform.equals(transformed)) {
result = resource;
} else {
result = BitmapResource.obtain(transformed, bitmapPool);
}
return result;
}
//com.bumptech.glide.load.resource.bitmap.CenterCrop:
protected Bitmap transform(BitmapPool pool, Bitmap toTransform, int outWidth, int outHeight) {
final Bitmap toReuse = pool.get(outWidth, outHeight, toTransform.getConfig() != null
? toTransform.getConfig() : Bitmap.Config.ARGB_8888);
Bitmap transformed = TransformationUtils.centerCrop(toReuse, toTransform, outWidth, outHeight);
if (toReuse != null && toReuse != transformed && !pool.put(toReuse)) {
toReuse.recycle();
}
return transformed;
}
由BitmapPool提供一个Bitmap作为下一步的Canvas载体。BitmapPool的实现类是LruBitmapPool，顾名思义是一个基于LRU方式的Bitmap缓存池，用于Bitmap的复用。
//com.bumptech.glide.load.resource.bitmap.TransformationUtils:
/**
* A potentially expensive operation to crop the given Bitmap so that it fills the given dimensions. This operation
* is significantly less expensive in terms of memory if a mutable Bitmap with the given dimensions is passed in
* as well.
*
* @param recycled A mutable Bitmap with dimensions width and height that we can load the cropped portion of toCrop
* into.
* @param toCrop The Bitmap to resize.
* @param width The width in pixels of the final Bitmap.
* @param height The height in pixels of the final Bitmap.
* @return The resized Bitmap (will be recycled if recycled is not null).
*/
public static Bitmap centerCrop(Bitmap recycled, Bitmap toCrop, int width, int height) {
if (toCrop == null) {
return null;
} else if (toCrop.getWidth() == width && toCrop.getHeight() == height) {
return toCrop;
}
// From ImageView/Bitmap.createScaledBitmap.
final float scale;
float dx = 0, dy = 0;
Matrix m = new Matrix();
if (toCrop.getWidth() * height > width * toCrop.getHeight()) {
scale = (float) height / (float) toCrop.getHeight();
dx = (width - toCrop.getWidth() * scale) * 0.5f;
} else {
scale = (float) width / (float) toCrop.getWidth();
dy = (height - toCrop.getHeight() * scale) * 0.5f;
}
m.setScale(scale, scale);
m.postTranslate((int) (dx + 0.5f), (int) (dy + 0.5f));
final Bitmap result;
if (recycled != null) {
result = recycled;
} else {
result = Bitmap.createBitmap(width, height, getSafeConfig(toCrop));
}
// We don't add or remove alpha, so keep the alpha setting of the Bitmap we were given.
TransformationUtils.setAlpha(toCrop, result);
Canvas canvas = new Canvas(result);
Paint paint = new Paint(PAINT_FLAGS);
canvas.drawBitmap(toCrop, m, paint);
return result;
}
在TransformationUtils的centerCrop方法中，根据目标尺寸调整矩阵并绘制结果。
与上面的流程类似，FitCenter类的transform方法调用TransformationUtils的fitCenter方法调整Bitmap。
继续看DecodeJob的transformEncodeAndTranscode方法。接下来调用writeTransformedToCache将转换结果写入磁盘缓存，再调用transcode方法进行转码。transcode方法中的transcoder的实际类型是GlideBitmapDrawableTranscoder。
//com.bumptech.glide.load.resource.transcode.GlideBitmapDrawableTranscoder:
@Override
public Resource<GlideBitmapDrawable> transcode(Resource<Bitmap> toTranscode) {
GlideBitmapDrawable drawable = new GlideBitmapDrawable(resources, toTranscode.get());
return new GlideBitmapDrawableResource(drawable, bitmapPool);
}
GlideBitmapDrawableTranscoder的transcode方法将Bitmap资源进行封装。到这里就结束了decodeFromSource的流程。
然后看decodeFromCache。
//com.bumptech.glide.load.engine.EngineRunnable:
private Resource<?> decodeFromCache() throws Exception {
Resource<?> result = null;
try {
result = decodeJob.decodeResultFromCache();
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Exception decoding result from cache: " + e);
}
}
if (result == null) {
result = decodeJob.decodeSourceFromCache();
}
return result;
}
先调用DecodeJob的decodeResultFromCache方法获取，获取失败则调用DecodeJob的decodeSourceFromCache方法。
//com.bumptech.glide.load.engine.DecodeJob:
/**
* Returns a transcoded resource decoded from transformed resource data in the disk cache, or null if no such
* resource exists.
*
* @throws Exception
*/
public Resource<Z> decodeResultFromCache() throws Exception {
if (!diskCacheStrategy.cacheResult()) {
return null;
}
long startTime = LogTime.getLogTime();
Resource<T> transformed = loadFromCache(resultKey);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Decoded transformed from cache", startTime);
}
startTime = LogTime.getLogTime();
Resource<Z> result = transcode(transformed);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Transcoded transformed from cache", startTime);
}
return result;
}
/**
* Returns a transformed and transcoded resource decoded from source data in the disk cache, or null if no such
* resource exists.
*
* @throws Exception
*/
public Resource<Z> decodeSourceFromCache() throws Exception {
if (!diskCacheStrategy.cacheSource()) {
return null;
}
long startTime = LogTime.getLogTime();
Resource<T> decoded = loadFromCache(resultKey.getOriginalKey());
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Decoded source from cache", startTime);
}
return transformEncodeAndTranscode(decoded);
}
decodeResultFromCache方法从磁盘缓存中获取对应Bitmap并将其转码。
decodeSourceFromCache方法从磁盘缓存中获取对应Bitmap并将其转换（因为是原尺寸，需要调整大小）。
到这里结束了EngineRunnable的decode方法的流程。
嗯？好像有什么不对？EngineRunnable的decode是decodeFromCache和decodeFromSource二选一，decodeFromCache也获取失败的话就没有然后了？
//com.bumptech.glide.load.engine.EngineRunnable:
@Override
public void run() {
if (isCancelled) {
return;
}
Exception exception = null;
Resource<?> resource = null;
try {
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);
}
}
private void onLoadFailed(Exception e) {
if (isDecodingFromCache()) {
stage = Stage.SOURCE;
manager.submitForSource(this);
} else {
manager.onException(e);
}
}
//com.bumptech.glide.load.engine.EngineJob:
@Override
public void submitForSource(EngineRunnable runnable) {
future = sourceService.submit(runnable);
}
缓存中没有结果的情况下会调用onLoadFailed方法，变更缓存策略重新放入线程池中执行，也就是从网络获取。这里的线程池是sourceService而不是上面的diskCacheService，分开两个线程池的用意何在呢？
得到了处理结果，接下来调用EngineRunnable的onLoadComplete方法将结果传入。
//com.bumptech.glide.load.engine.EngineRunnable:
private void onLoadComplete(Resource resource) {
manager.onResourceReady(resource);
}
onLoadComplete方法调用了EngineJob的onResourceReady方法。
//com.bumptech.glide.load.engine.EngineJob:
@Override
public void onResourceReady(final Resource<?> resource) {
this.resource = resource;
MAIN_THREAD_HANDLER.obtainMessage(MSG_COMPLETE, this).sendToTarget();
}
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);
for (ResourceCallback cb : cbs) {
if (!isInIgnoredCallbacks(cb)) {
engineResource.acquire();
cb.onResourceReady(engineResource);
}
}
// Our request is complete, so we can release the resource.
engineResource.release();
}
onResourceReady方法中向Handler传递消息并由MainThreadCallback处理消息 ，也就切换到了主线程。handleResultOnMainThread方法会调用GenericRequest的onResourceReady方法。
//com.bumptech.glide.request.GenericRequest:
@Override
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);
}
private void onResourceReady(Resource<?> resource, R result) {
// We must call isFirstReadyResource before setting status.
boolean isFirstResource = isFirstReadyResource();
status = Status.COMPLETE;
this.resource = resource;
if (requestListener == null || !requestListener.onResourceReady(result, model, target, loadedFromMemoryCache,
isFirstResource)) {
GlideAnimation<R> animation = animationFactory.build(loadedFromMemoryCache, isFirstResource);
target.onResourceReady(result, animation);
}
notifyLoadSuccess();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("Resource ready in " + LogTime.getElapsedMillis(startTime) + " size: "
+ (resource.getSize() * TO_MEGABYTE) + " fromCache: " + loadedFromMemoryCache);
}
}
onResourceReady方法调用GlideDrawableImageViewTarget的onResourceReady方法。
//com.bumptech.glide.request.target.GlideDrawableImageViewTarget:
@Override
public void onResourceReady(GlideDrawable resource, GlideAnimation<? super GlideDrawable> animation) {
if (!resource.isAnimated()) {
//TODO: Try to generalize this to other sizes/shapes.
// This is a dirty hack that tries to make loading square thumbnails and then square full images less costly
// by forcing both the smaller thumb and the larger version to have exactly the same intrinsic dimensions.
// If a drawable is replaced in an ImageView by another drawable with different intrinsic dimensions,
// the ImageView requests a layout. Scrolling rapidly while replacing thumbs with larger images triggers
// lots of these calls and causes significant amounts of jank.
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());
}
}
super.onResourceReady(resource, animation);
this.resource = resource;
resource.setLoopCount(maxLoopCount);
resource.start();
}
/**
* Sets the drawable on the view using
* {@link android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)}.
*
* @param resource The {@link android.graphics.drawable.Drawable} to display in the view.
*/
@Override
protected void setResource(GlideDrawable resource) {
view.setImageDrawable(resource);
}
//com.bumptech.glide.request.target.ImageViewTarget:
@Override
public void onResourceReady(Z resource, GlideAnimation<? super Z> glideAnimation) {
if (glideAnimation == null || !glideAnimation.animate(resource, this)) {
setResource(resource);
}
}
protected abstract void setResource(Z resource);
GlideDrawableImageViewTarget的onResourceReady方法调用其父类ImageViewTarget的onResourceReady方法，而ImageViewTarget的onResourceReady方法中调用的抽象方法setResource在子类GlideDrawableImageViewTarget中实现，该方法中调用了ImageView的setImageDrawable方法设置图像。至此，整个加载流程就完成了。
下图是忽略部分细节的加载流程方法调用示意。
