RequestBuilder是什么
它是一個用于處理設(shè)置選項(xiàng)和啟動加載的類，可以用來監(jiān)聽資源的加載成功與否(RequestListener)，加載失敗(error)和縮略圖(thumbnail)，創(chuàng)建Target和Request等。
RequestBuilder怎么創(chuàng)建的
在RequestManger里我們調(diào)用load()加載資源的時候，最終會調(diào)用RequestBuilder的構(gòu)造方法把RequestManager和資源的類型賦值進(jìn)去并創(chuàng)建一個RequestBuilder。
GlideApp.with(context)
.load(url)
.into(imageView)
//RequestManager
public RequestBuilder<Drawable> load(@Nullable String string) {
return asDrawable().load(string);
}
public RequestBuilder<Drawable> asDrawable() {
return as(Drawable.class);
}
public <ResourceType> RequestBuilder<ResourceType> as(
@NonNull Class<ResourceType> resourceClass) {
return new RequestBuilder<>(glide, this, resourceClass, context);
}
load()里面做了什么
這里只是簡單的進(jìn)行賦值，并把isModelSet設(shè)置為true。
public RequestBuilder<TranscodeType> load(@Nullable String string) {
return loadGeneric(string);
}
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
this.model = model;
isModelSet = true;
return this;
}
into()里面做了什么
首先會判斷如果之前沒有設(shè)置轉(zhuǎn)換比如調(diào)用centerCrop()并且允許轉(zhuǎn)換而且imageView的scaleType不為null，則根據(jù)它的scaleType設(shè)置相應(yīng)的轉(zhuǎn)換。然后創(chuàng)建了一個ImageViewTarget對象并且傳入了into的重載方法。
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
BaseRequestOptions<?> requestOptions = this;
if (!requestOptions.isTransformationSet()
&& requestOptions.isTransformationAllowed()
&& view.getScaleType() != null) {
switch (view.getScaleType()) {
case CENTER_CROP:
requestOptions = requestOptions.clone().optionalCenterCrop();
break;
case CENTER_INSIDE:
requestOptions = requestOptions.clone().optionalCenterInside();
break;
case FIT_CENTER:
case FIT_START:
case FIT_END:
requestOptions = requestOptions.clone().optionalFitCenter();
break;
case FIT_XY:
requestOptions = requestOptions.clone().optionalCenterInside();
break;
case CENTER:
case MATRIX:
default:
// Do nothing.
}
}
return into(
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions,
Executors.mainThreadExecutor());
}
ImageViewTarget的創(chuàng)建
這里使用了工廠模式來創(chuàng)建ViewTarget，由上面可知我們的資源類型是Drawable，則最終會創(chuàng)建一個DrawableImageViewTarget。
public <X> ViewTarget<ImageView, X> buildImageViewTarget(
@NonNull ImageView imageView, @NonNull Class<X> transcodeClass) {
return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
}
public <Z> ViewTarget<ImageView, Z> buildTarget(@NonNull ImageView view,
@NonNull Class<Z> clazz) {
if (Bitmap.class.equals(clazz)) {
return (ViewTarget<ImageView, Z>) new BitmapImageViewTarget(view);
} else if (Drawable.class.isAssignableFrom(clazz)) {
return (ViewTarget<ImageView, Z>) new DrawableImageViewTarget(view);
} else {
throw new IllegalArgumentException(
"Unhandled class: " + clazz + ", try .as*(Class).transcode(ResourceTranscoder)");
}
}
Request的創(chuàng)建
這里通過buildRequest()方法創(chuàng)建了一個Request，并且判斷是否和Target之前的Request相等以及如果使用內(nèi)存緩存的話則回收掉剛剛創(chuàng)建的Request。
<Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
Executor callbackExecutor) {
return into(target, targetListener, /*options=*/ this, callbackExecutor);
}
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> options,
Executor callbackExecutor) {
Preconditions.checkNotNull(target);
if (!isModelSet) {
//如果沒有調(diào)用load()方法則會拋異常
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
Request request = buildRequest(target, targetListener, options, callbackExecutor);
Request previous = target.getRequest(); //調(diào)用view.getTag()獲取Request
if (request.isEquivalentTo(previous)
&& !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
request.recycle();
if (!Preconditions.checkNotNull(previous).isRunning()) {
previous.begin(); //如果之前的Request不是正在運(yùn)行的，則開始執(zhí)行
}
return target;
}
requestManager.clear(target); //清除request并釋放資源
target.setRequest(request); //調(diào)用view.setTag()保存request
requestManager.track(target, request);
return target;
}
Request的具體創(chuàng)建
通過幾個重載方法，把一堆參數(shù)最后傳給了SingleRequest的構(gòu)造方法來創(chuàng)建SingleRequest，由于Request可能會比較多，所以Glide使用了對象池來對SingleRequest進(jìn)行復(fù)用。
private Request buildRequest(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
return buildRequestRecursive(
target,
targetListener,
/*parentCoordinator=*/ null,
transitionOptions,
requestOptions.getPriority(),
requestOptions.getOverrideWidth(),
requestOptions.getOverrideHeight(),
requestOptions,
callbackExecutor);
}
private Request buildRequestRecursive(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
@Nullable RequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
Request mainRequest =
buildThumbnailRequestRecursive(
target,
targetListener,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
requestOptions,
callbackExecutor);
if (errorRequestCoordinator == null) {
return mainRequest;
}
}
private Request buildThumbnailRequestRecursive(
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
@Nullable RequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
return obtainRequest(
target,
targetListener,
requestOptions,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
}
private Request obtainRequest(
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> requestOptions,
RequestCoordinator requestCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
Executor callbackExecutor) {
return SingleRequest.obtain(
context,
glideContext,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
targetListener,
requestListeners,
requestCoordinator,
glideContext.getEngine(),
transitionOptions.getTransitionFactory(),
callbackExecutor);
}
public static <R> SingleRequest<R> obtain(
Context context,
GlideContext glideContext,
Object model,
Class<R> transcodeClass,
BaseRequestOptions<?> requestOptions,
int overrideWidth,
int overrideHeight,
Priority priority,
Target<R> target,
RequestListener<R> targetListener,
@Nullable List<RequestListener<R>> requestListeners,
RequestCoordinator requestCoordinator,
Engine engine,
TransitionFactory<? super R> animationFactory,
Executor callbackExecutor) {
@SuppressWarnings("unchecked") SingleRequest<R> request =
(SingleRequest<R>) POOL.acquire();
if (request == null) {
request = new SingleRequest<>();
}
request.init(
context,
glideContext,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
targetListener,
requestListeners,
requestCoordinator,
engine,
animationFactory,
callbackExecutor);
return request;
}
到此Target和Request都創(chuàng)建完成了，接著會調(diào)用RequestManger的track()把它們傳遞進(jìn)去，在上文Glide源碼解析之監(jiān)聽生命周期我們介紹過TargetTracker和RequestTracker，他們追蹤的Target和Request就是在這里賦值的。
//RequestManager
synchronized void track(@NonNull Target<?> target, @NonNull Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}
//RequestTracker
/**
* 對request開始追蹤
*/
public void runRequest(@NonNull Request request) {
requests.add(request);
if (!isPaused) {
request.begin(); //啟動加載
} else {
request.clear();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Paused, delaying request");
}
pendingRequests.add(request);
}
}
