Glide源码阅读之原型模式【TransitionOptions】【BaseRequestOptions】【RequestBuilder】
定义
菜鸟教程
原型模式（Prototype Pattern）是用于创建重复的对象，同时又能保证性能。这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方式。
这种模式是实现了一个原型接口，该接口用于创建当前对象的克隆。当直接创建对象的代价比较大时，则采用这种模式。例如，一个对象需要在一个高代价的数据库操作之后被创建。我们可以缓存该对象，在下一个请求时返回它的克隆，在需要的时候更新数据库，以此来减少数据库调用
大话设计模式
用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象
《Android源码设计模式解析与实践》
特点
最大的特点是：implements Cloneable；但凡实现Cloneable接口的一般都满足原型模式。当然也不排除有其他变种情况，不过目前没有碰到。如果有请留言分享，或者后期我碰到后再补充。
注意事项：
与通过对一个类进行实例化来构造新对象不同的是，原型模式是通过拷贝一个现有对象生成新对象的。浅拷贝实现 Cloneable，重写，深拷贝是通过实现 Serializable 读取二进制流。
使用场景
- 简历模板
- 历史文档修改记录（比如：飞书、腾讯等在线编辑文档）
浅拷贝、深拷贝
浅拷贝
被复制对象的所有变量都含有与原来的对象相同的值，而所有的对其他对象的引用都仍然指向原来的对象。
深拷贝
把引用对象的变量指向复制过的新对象，而不是原有的被引用的对象
Glide原型模式应用
包路径：com.bumptech.glide.TransitionOptions
/**
* A base class for setting a transition to use on a resource when a load completes.
*
* @param <CHILD> The implementation of this class to return to chain methods.
* @param <TranscodeType> The type of resource that will be animated.
*/
public abstract class TransitionOptions<
CHILD extends TransitionOptions<CHILD, TranscodeType>, TranscodeType>
implements Cloneable {
private TransitionFactory<? super TranscodeType> transitionFactory = NoTransition.getFactory();
/**
* Removes any existing animation put on the builder. Will be overridden by subsequent calls that
* put an animation.
*
* @return This request builder.
*/
@NonNull
public final CHILD dontTransition() {
return transition(NoTransition.getFactory());
}
/**
* Sets an {@link android.view.animation.Animation} to run on the wrapped target when an resource
* load finishes. Will only be run if the resource was loaded asynchronously (i.e. was not in the
* memory cache).
*
* @param viewAnimationId The resource id of the {@link android.view.animation} to use as the
* transition.
* @return This request builder.
*/
@NonNull
public final CHILD transition(int viewAnimationId) {
return transition(new ViewAnimationFactory<>(viewAnimationId));
}
/**
* Sets an animator to run a {@link android.view.ViewPropertyAnimator} on a view that the target
* may be wrapping when a resource load finishes. Will only be run if the load was loaded
* asynchronously (i.e. was not in the memory cache).
*
* @param animator The {@link com.bumptech.glide.request.transition.ViewPropertyTransition
* .Animator} to run.
* @return This request builder.
*/
@NonNull
public final CHILD transition(@NonNull ViewPropertyTransition.Animator animator) {
return transition(new ViewPropertyAnimationFactory<>(animator));
}
/**
* Uses the given {@link TransitionFactory} to build a {@link
* com.bumptech.glide.request.transition.Transition} for each request started with these {@code
* TransitionOptions}.
*
* @return This request builder.
*/
@NonNull
public final CHILD transition(
@NonNull TransitionFactory<? super TranscodeType> transitionFactory) {
this.transitionFactory = Preconditions.checkNotNull(transitionFactory);
return self();
}
@SuppressWarnings({
// cast to CHILD is safe given the generic argument represents the object's runtime class
"unchecked",
// CHILD is the correct class name.
"PMD.CloneMethodReturnTypeMustMatchClassName",
// we don't want to throw to be user friendly
"PMD.CloneThrowsCloneNotSupportedException"
})
@Override
public final CHILD clone() {
try {
return (CHILD) super.clone();
} catch (CloneNotSupportedException e) {
throw new RuntimeException(e);
}
}
final TransitionFactory<? super TranscodeType> getTransitionFactory() {
return transitionFactory;
}
@SuppressWarnings("unchecked")
private CHILD self() {
return (CHILD) this;
}
}
被RequestBuilder调用，同时RequestBuilder也是原型模式，两者结合正好说明浅拷贝和深拷贝。TransitionOptions属于浅拷贝那种
RequestBuilder调用了TransitionOptions的clone()属于深拷贝那种。当然深浅拷贝取舍也是根据实际业务场景设定的。
/**
* A generic class that can handle setting options and staring loads for generic resource types.
*
* @param <TranscodeType> The type of resource that will be delivered to the {@link
* com.bumptech.glide.request.target.Target}.
*/
// Public API.
@SuppressWarnings({"unused", "WeakerAccess"})
public class RequestBuilder<TranscodeType> extends BaseRequestOptions<RequestBuilder<TranscodeType>>
implements Cloneable, ModelTypes<RequestBuilder<TranscodeType>> {
。。。
@NonNull
@SuppressWarnings("unchecked")
private TransitionOptions<?, ? super TranscodeType> transitionOptions;
/**
* Returns a copy of this request builder with all of the options put so far on this builder.
*
* <p>This method returns a "deep" copy in that all non-immutable arguments are copied such that
* changes to one builder will not affect the other builder. However, in addition to immutable
* arguments, the current model is not copied so changes to the model will affect both builders.
*/
@SuppressWarnings({
// we don't want to throw to be user friendly
"PMD.CloneThrowsCloneNotSupportedException"
})
@CheckResult
@Override
public RequestBuilder<TranscodeType> clone() {
RequestBuilder<TranscodeType> result = super.clone();
result.transitionOptions = result.transitionOptions.clone();
if (result.requestListeners != null) {
result.requestListeners = new ArrayList<>(result.requestListeners);
}
if (result.thumbnailBuilder != null) {
result.thumbnailBuilder = result.thumbnailBuilder.clone();
}
if (result.errorBuilder != null) {
result.errorBuilder = result.errorBuilder.clone();
}
return result;
}
再补充一个BaseRequestOptions
/**
* A base object to allow method sharing between {@link RequestOptions} and {@link
* com.bumptech.glide.RequestBuilder}.
*
* <p>This class is not meant for general use and may change at any time.
*
* @param <T> The particular child implementation
*/
@SuppressWarnings({"PMD.UseUtilityClass", "unused"})
public abstract class BaseRequestOptions<T extends BaseRequestOptions<T>> implements Cloneable {
private static final int UNSET = -1;
private static final int SIZE_MULTIPLIER = 1 << 1;
。。。
/**
* Returns a copy of this request builder with all of the options put so far on this builder.
*
* <p>This method returns a "deep" copy in that all non-immutable arguments are copied such that
* changes to one builder will not affect the other builder. However, in addition to immutable
* arguments, the current model is not copied copied so changes to the model will affect both
* builders.
*
* <p>Even if this object was locked, the cloned object returned from this method will not be
* locked.
*/
@SuppressWarnings({
"unchecked",
// we don't want to throw to be user friendly
"PMD.CloneThrowsCloneNotSupportedException",
// The types we're using here do this automatically.
"PMD.CloneMethodReturnTypeMustMatchClassName"
})
@CheckResult
@Override
public T clone() {
try {
BaseRequestOptions<?> result = (BaseRequestOptions<?>) super.clone();
result.options = new Options();
result.options.putAll(options);
result.transformations = new CachedHashCodeArrayMap<>();
result.transformations.putAll(transformations);
result.isLocked = false;
result.isAutoCloneEnabled = false;
return (T) result;
} catch (CloneNotSupportedException e) {
throw new RuntimeException(e);
}
}
。。。。
总结
具体的业务上和功能上的介绍就免了，如果有兴趣可以自行翻译。本文介绍的是原型模式的结构以及深浅拷贝的说明。聚焦设计模式解析，争取读完一个模式解析即可在项目上进行应用。
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