基本调用流程
这一篇文章我们从源码的角度分析Glide实现，首先我们从一句最简单的使用方式来探索他的设计与实现，可以看到下面这句话是最基础的使用
Glide.with(this)
.load(R.raw.large_giphy_logo)
.into(giphyLogoView);
接下来我们一步一步的跟踪他的调用过程，首先我们看到他调用了Glide的with方法并传入了自己的引用，我们可以看到这方法的实现如下：
public static RequestManager with(Activity activity) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(activity);
}
他调用了RequestManagerRetriever的方法获取了一个RequestManagerRetriever然后在调用get方法获取了一个RequestManager，到这里我们大概基本明白了with方法做的是将当前引用（Activity，Fragment）传递进去并获取一个和当前引用绑定的RequestManager，到这里大家应该能明白了为什么说Glide绑定了界面的生命周期了吧
接着调用了RequestManager的load方法，可以看到这一步创建了RequestBuilder
public RequestBuilder<Drawable> load(@Nullable Object model) {
return asDrawable().load(model);
}
最后调用到了loadGeneric方法
public RequestBuilder<TranscodeType> load(@Nullable Object model) {
return loadGeneric(model);
}
不过从这个方法我们可以看到他只是将传递进来的资源保存了，现在还没有发送真正的网络请求
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
this.model = model;
isModelSet = true;
return this;
}
然后调用了RequestBuilder的into方法
public Target<TranscodeType> into(ImageView view) {
Util.assertMainThread();
Preconditions.checkNotNull(view);
if (!requestOptions.isTransformationSet()
&& requestOptions.isTransformationAllowed()
&& view.getScaleType() != null) {
if (requestOptions.isLocked()) {
requestOptions = requestOptions.clone();
}
switch (view.getScaleType()) {
case CENTER_CROP:
requestOptions.optionalCenterCrop(context);
break;
case CENTER_INSIDE:
requestOptions.optionalCenterInside(context);
break;
case FIT_CENTER:
case FIT_START:
case FIT_END:
requestOptions.optionalFitCenter(context);
break;
//$CASES-OMITTED$
default:
// Do nothing.
}
}
return into(context.buildImageViewTarget(view, transcodeClass));
}
在这个方法里面，主要判断了是否设置了Transformation如果设置了，然后根据相应的规则变换bitmap，最后调用了这个into方法
public <Y extends Target<TranscodeType>> Y into(@NonNull Y target) {
Util.assertMainThread();
Preconditions.checkNotNull(target);
if (!isModelSet) {
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
Request previous = target.getRequest();
if (previous != null) {
requestManager.clear(target);
}
requestOptions.lock();
Request request = buildRequest(target);
target.setRequest(request);
requestManager.track(target, request);
return target;
}
在这方法中创建了Request，然后调用requestManager的track方法去执行这个request
void track(Target<?> target, Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}
我们再来查看下buildRequest方法
private Request buildRequest(Target<TranscodeType> target) {
return buildRequestRecursive(target, null, transitionOptions, requestOptions.getPriority(),
requestOptions.getOverrideWidth(), requestOptions.getOverrideHeight());
}
private Request buildRequestRecursive(Target<TranscodeType> target,
@Nullable ThumbnailRequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority, int overrideWidth, int overrideHeight) {
if (thumbnailBuilder != null) {
// Recursive case: contains a potentially recursive thumbnail request builder.
if (isThumbnailBuilt) {
throw new IllegalStateException("You cannot use a request as both the main request and a "
+ "thumbnail, consider using clone() on the request(s) passed to thumbnail()");
}
TransitionOptions<?, ? super TranscodeType> thumbTransitionOptions =
thumbnailBuilder.transitionOptions;
if (DEFAULT_ANIMATION_OPTIONS.equals(thumbTransitionOptions)) {
thumbTransitionOptions = transitionOptions;
}
Priority thumbPriority = thumbnailBuilder.requestOptions.isPrioritySet()
? thumbnailBuilder.requestOptions.getPriority() : getThumbnailPriority(priority);
int thumbOverrideWidth = thumbnailBuilder.requestOptions.getOverrideWidth();
int thumbOverrideHeight = thumbnailBuilder.requestOptions.getOverrideHeight();
if (Util.isValidDimensions(overrideWidth, overrideHeight)
&& !thumbnailBuilder.requestOptions.isValidOverride()) {
thumbOverrideWidth = requestOptions.getOverrideWidth();
thumbOverrideHeight = requestOptions.getOverrideHeight();
}
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
Request fullRequest = obtainRequest(target, requestOptions, coordinator,
transitionOptions, priority, overrideWidth, overrideHeight);
isThumbnailBuilt = true;
// Recursively generate thumbnail requests.
Request thumbRequest = thumbnailBuilder.buildRequestRecursive(target, coordinator,
thumbTransitionOptions, thumbPriority, thumbOverrideWidth, thumbOverrideHeight);
isThumbnailBuilt = false;
coordinator.setRequests(fullRequest, thumbRequest);
return coordinator;
} else if (thumbSizeMultiplier != null) {
// Base case: thumbnail multiplier generates a thumbnail request, but cannot recurse.
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
Request fullRequest = obtainRequest(target, requestOptions, coordinator, transitionOptions,
priority, overrideWidth, overrideHeight);
BaseRequestOptions<?> thumbnailOptions = requestOptions.clone()
.sizeMultiplier(thumbSizeMultiplier);
Request thumbnailRequest = obtainRequest(target, thumbnailOptions, coordinator,
transitionOptions, getThumbnailPriority(priority), overrideWidth, overrideHeight);
coordinator.setRequests(fullRequest, thumbnailRequest);
return coordinator;
} else {
// Base case: no thumbnail.
return obtainRequest(target, requestOptions, parentCoordinator, transitionOptions, priority,
overrideWidth, overrideHeight);
}
}
可以看到最后调用了buildRequestRecursive来创建一个Request，在这方法里面通过判断是否设置了thumbnail来创建不同类型的Request，如果没有设置就会创建最基本的请求，也就是SingleRequest
private Request obtainRequest(Target<TranscodeType> target,
BaseRequestOptions<?> requestOptions, RequestCoordinator requestCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions, Priority priority,
int overrideWidth, int overrideHeight) {
requestOptions.lock();
return SingleRequest.obtain(
context,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
requestListener,
requestCoordinator,
context.getEngine(),
transitionOptions.getTransitionFactory());
}
到这里大家可以看到Glide的源码可以说是非常复杂的，总感觉有时候用到项目里是不是有点太重了，就加载个图片，你看看搞了这么多代码~~
一些设计技巧
绑定界面的生命周期
在Glide中可以看到所有的请求都是和当前界面绑定的，比如：activity执行onStop时，其相应的请求应该暂停，那他是怎么绑定的呢，简单来讲就是在当前activity中绑定一个fragment，这样我们就能通过这个fragment获取到相应的生命周期，然后回调到你要处理的地方，然后在作出相应的处理，如果代码：
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void bindLifeCycle(LifeCycleActivity activity) {
FragmentManager fm = activity.getFragmentManager();
//将一个fragment绑定到当前界面，这样就能获取到了当前界面的生命周期了
LifeCycleFragment current = new LifeCycleFragment();
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
}
这样我们就能在LifeCycleFragment中获取到相应的生命周期了
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class LifeCycleFragment extends Fragment {
private static final String TAG = "LifeCycleFragment";
@Override
public void onStart() {
super.onStart();
//TODO 这里回调你的生命周期状态
Log.d(TAG,"onStart");
}
@Override
public void onStop() {
super.onStop();
Log.d(TAG,"onStop");
}
@Override
public void onDestroy() {
super.onDestroy();
Log.d(TAG,"onDestroy");
}
}
参考：https://github.com/android-cn/android-open-project-analysis/tree/master/tool-lib/image-cache/glide
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