Glide学习笔记

Anatomy of a load（加载过程中涉及的几个概念）

The set of registered components, including both those registered by default in Glide and those registered in Modules are used to define a set of load paths. Each load path is a step by step progression from the the Model provided to load() to the Resource type specified by as(). A load path consists (roughly) of the following steps:1. Model -> Data (handled by ModelLoaders)->Encoders2. Data -> Resource (handled by ResourceDecoders)->ResourceEncoders3. Resource -> Transcoded Resource (optional, handled by ResourceTranscoders).Encoders can write Data to Glide’s disk cache cache before step 2. ResourceEncoders can write Resource’s to Glide’s disk cache before step 3.When a request is started, Glide will attempt all available paths from the Model to the requested Resource type. A request will succeed if any load path succeeds. A request will fail only if all available load paths fail.

如何自动回收bitmap？

Glide 的魅力是自动处理请求的取消，清除 ImageView，并加载正确的图片到对应的 ImageView。into:Sets the ImageView the resource will be loaded into, cancels any existing loads into the view, and frees any resources Glide may have previously loaded into the view so they may be reused.public <Z> Target<Z> buildTarget(ImageView view, Class<Z> clazz):Sets the android resource id to use in conjunction with View.setTag(int, Object) to store temporary state allowing loads to be automatically cancelled and resources re-used in scrolling lists.To detect View reuse in android.widget.ListView or any android.view.ViewGroup that reuses views, this class uses the View.setTag(Object) method to store some metadata so that if a view is reused, any previous loads or resources from previous loads can be cancelled or reused.

如何跟随生命周期自动停止加载？

A view-less Fragment used to safely store an RequestManager that can be used to start, stop and manage Glide requests started for targets the fragment or activity this fragment is a child of.

@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)RequestManagerFragment getRequestManagerFragment(    final android.app.FragmentManager fm, android.app.Fragment parentHint) {  RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);  if (current == null) {    current = pendingRequestManagerFragments.get(fm);    if (current == null) {      current = new RequestManagerFragment();      current.setParentFragmentHint(parentHint);      pendingRequestManagerFragments.put(fm, current);      fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();//增加一个Fragment到Activity中监听生命周期      handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();    }  }  return current;}

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

自定义下载接口？

注册ModelLoader， 返回stream

缓存？

Glide 的缓存实现是基于 Picasso。缓存实现的大小是依赖于设备的磁盘大小。

By default, Glide checks multiple layers of caches before starting a new request for an image:1. Active resources - Is this image displayed in another View right now?2. Memory cache - Was this image recently loaded and still in memory?3. Resource - Has this image been decoded, transformed, and written to the disk cache before?4. Data - Was the data this image was obtained from written to the disk cache before?The first two steps check to see if the resource is in memory and if so, return the image immediately. The second two steps check to see if the image is on disk and return quickly, but asynchronously.

Cache Keys的生成

In Glide 4, all cache keys contain at least two elements:1. The model the load** is requested for (File, Uri, Url) (If you are using a custom model, it needs to correctly implements hashCode() and equals()2. An optional SignatureIn fact, the cache keys for steps 1-3 (Active resources, memory cache, resource disk cache) also include a number of other pieces of data including:1. The width and height2. The optional Transformation3. Any added Options4. The requested data type (Bitmap, GIF, etc)The keys used for active resources and the memory cache also differ slightly from those used from the resource disk cache to accomodate in memory Options like those that affect the configuration of the Bitmap or other decode time only parameters.To generate the name of disk cache keys on disk, the individual elements of the keys are hashed to create a single String key, which is then used as the file name in the disk cache.