Glide源码阅读之工厂模式3【TransitionFactory】【Transition】

参考阅读：

Glide多种组合使用方式记录–没有全部亲测，大家可以根据实际需要选用
Glide设计模式之工厂模式1【ModelLoaderFactory】
Glide设计模式之工厂模式2【DiskCache.Factory】
Glide工厂模式3【TransitionFactory】【Transition】
Glide设计模式之工厂模式4总结

Transition

包路径：com.bumptech.glide.request.transition.Transition
Transition接口业务是TransitionFactory的生产对象目标

/**
* An interface that allows a transition to be applied to {@link android.view.View}s in {@link
* com.bumptech.glide.request.target.Target}s in across resource types. Targets that wrap views will
* be able to provide all of the necessary arguments and start the transition. Those that do not
* will be unable to provide the necessary arguments and will therefore be forced to ignore the
* transition. This interface is a compromise that allows view specific transition in Glide's
* complex world of arbitrary resource types and arbitrary target types.
*
* @param <R> The type of the resource whose entrance will be transitioned.
*/
public interface Transition<R> {
。。。

一个允许跨资源类型将转换应用到目标中的视图的接口。包装视图的目标将能够提供所有必要的参数并开始转换。不这样做的那将无法提供必要的参数，因此将被迫忽视过渡。这个接口是一种折衷，它允许在Glide的任意资源类型和任意目标类型的复杂世界中查看特定的过渡。

类型参数:
R -其入口将被转换的资源的类型。

/**
* An interface wrapping a view that exposes the necessary methods to run the various types of
* android animations as transitions: ({@link ViewTransition}, {@link ViewPropertyTransition} and
* animated {@link android.graphics.drawable.Drawable}s).
*/
interface ViewAdapter {
/** Returns the wrapped {@link android.view.View}. */
返回被包装的视图。
View getView();

一个接口包装了一个视图，它公开了必要的方法来运行各种类型的android动画的过渡(ViewTransition, ViewPropertyTransition和animated Drawables)。

/**
* Returns the current drawable being displayed in the view, or null if no such drawable exists
* (or one cannot be retrieved).
*/
@Nullable
Drawable getCurrentDrawable();

返回视图中显示的当前绘制对象，如果不存在该绘制对象(或无法检索)，则返回null。

/**
* Sets the current drawable (usually an animated drawable) to display in the wrapped view.
*
* @param drawable The drawable to display in the wrapped view.
*/
void setDrawable(Drawable drawable);
}

设置当前绘制对象(通常是动画绘制对象)显示在换行视图中。

/**
* Animates from the previous {@link android.graphics.drawable.Drawable} that is currently being
* displayed in the given view, if not null, to the new resource that should be displayed in the
* view.
*
* @param current The new resource that will be displayed in the view.
* @param adapter The {@link Transition.ViewAdapter} wrapping a view that can at least return an
*
{@link android.view.View} from {@link Transition.ViewAdapter#getView()}.
* @return True if in the process of running the transition, the new resource was put on the view,
*
false if the caller needs to manually put the current resource on the view.
*/
boolean transition(R current, ViewAdapter adapter);
}

从当前在给定视图中显示的前一个Drawable动画，如果不为空，到应该在视图中显示的新资源。
参数:
current—将在视图中显示的新资源。
适配器-过渡。ViewAdapter包装的视图至少可以从Transition.ViewAdapter.getView()返回一个视图。
返回:
如果在运行转换的过程中，新资源被放到视图上，则为True，如果调用者需要手动将当前资源放到视图上，则为false。

使用

GlideApp.with(context)
.load(url)
.transition(withCrossFade(factory))
.diskCacheStrategy(DiskCacheStrategy.ALL)
.placeholder(R.color.placeholder)
.into(imageView);

很显然和设置转换**.transition(withCrossFade(factory))**相关

TransitionFactory

包路径：com.bumptech.glide.request.transition.TransitionFactory

/**
* A factory class that can produce different {@link Transition}s based on the state of the request.
*
* @param <R> The type of resource that needs to be animated into the target.
*/
public interface TransitionFactory<R> {

一个工厂类，它可以根据请求的状态生成不同的转换。
类型参数:
R -需要动画到目标中的资源的类型。

/**
* Returns a new {@link Transition}.
*
* @param dataSource The {@link com.bumptech.glide.load.DataSource} the resource was loaded from.
* @param isFirstResource True if this is the first resource to be loaded into the target.
*/
Transition<R> build(DataSource dataSource, boolean isFirstResource);
}

返回一个新的过渡。
参数:
数据源-资源被加载的数据源。
isFirstResource -如果这是加载到目标中的第一个资源，则为True。

具体的实现工厂类如下列表

• BitmapContainerTransitionFactory
• BitmapTransitionFactory
• DrawableCrossFadeFactory
• NoTransition.NoAnimationFactory
• ViewAnimationFactory
• ViewPropertyAnimationFactory

BitmapContainerTransitionFactory

包路径：com.bumptech.glide.request.transition.BitmapContainerTransitionFactory

/**
* A {@link TransitionFactory} for complex types that have a {@link android.graphics.Bitmap} inside.
* The transitioning bitmap is wrapped in a {@link android.graphics.drawable.BitmapDrawable}. Most
* commonly used with {@link DrawableCrossFadeFactory}.
*
* @param <R> The type of the composite object that contains the {@link android.graphics.Bitmap} to
*
be transitioned.
*/
public abstract class BitmapContainerTransitionFactory<R> implements TransitionFactory<R> {
。。。

一个内部有位图的复杂类型的TransitionFactory。转换位图被包装在BitmapDrawable中。最常用的是drawablecrosfadefactory。
类型参数:
R -包含要转换的位图的复合对象的类型。

 @Override
public Transition<R> build(DataSource dataSource, boolean isFirstResource) {
Transition<Drawable> transition = realFactory.build(dataSource, isFirstResource);
return new BitmapGlideAnimation(transition);
}

private final class BitmapGlideAnimation implements Transition<R> {
private final Transition<Drawable> transition;
BitmapGlideAnimation(Transition<Drawable> transition) {
this.transition = transition;
}
@Override
public boolean transition(R current, ViewAdapter adapter) {
Resources resources = adapter.getView().getResources();
Drawable currentBitmap = new BitmapDrawable(resources, getBitmap(current));
return transition.transition(currentBitmap, adapter);
}
}

BitmapTransitionFactory

包路径：com.bumptech.glide.request.transition.BitmapTransitionFactory

/**
* A {@link TransitionFactory} for {@link android.graphics.Bitmap}s that uses a Drawable transition
* factory to transition from an existing drawable already visible on the target to the new bitmap.
*
* @see BitmapContainerTransitionFactory
*/
public class BitmapTransitionFactory extends BitmapContainerTransitionFactory<Bitmap> {
public BitmapTransitionFactory(@NonNull TransitionFactory<Drawable> realFactory) {
super(realFactory);
}
@Override
@NonNull
protected Bitmap getBitmap(@NonNull Bitmap current) {
return current;
}
}

用于位图的TransitionFactory，它使用一个Drawable转换工厂从一个已经在目标上可见的可绘制对象转换到新的位图。

DrawableCrossFadeFactory

/**
* A factory class that produces a new {@link Transition} that varies depending on whether or not
* the drawable was loaded from the memory cache and whether or not the drawable is the first image
* to be put on the target.
*
* <p>Resources are usually loaded from the memory cache just before the user can see the view, for
* example when the user changes screens or scrolls back and forth in a list. In those cases the
* user typically does not expect to see a transition. As a result, when the resource is loaded from
* the memory cache this factory produces an {@link NoTransition}.
*/
// Public API.
@SuppressWarnings("WeakerAccess")
public class DrawableCrossFadeFactory implements TransitionFactory<Drawable> {
。。。

一个工厂类，它生成一个新的Transition，这个Transition取决于绘制对象是否从内存缓存中加载，以及绘制对象是否是第一个放到目标上的图像。
资源通常在用户可以看到视图之前从内存缓存加载，例如当用户更改屏幕或在列表中来回滚动时。在这些情况下，用户通常不希望看到转换。因此，当资源从内存缓存加载时，这个工厂产生一个NoTransition

NoTransition.NoAnimationFactory

/**
* A factory that always returns the same {@link NoTransition}.
*
* @param <R> the resource type that will be transitioned into a {@link
*
com.bumptech.glide.request.target.Target}.
*/
public static class NoAnimationFactory<R> implements TransitionFactory<R> {
@SuppressWarnings("unchecked")
@Override
public Transition<R> build(DataSource dataSource, boolean isFirstResource) {
return (Transition<R>) NO_ANIMATION;
}
}

总是返回相同NoTransition的工厂。
类型参数:
R -将被转换到Target的资源类型。

ViewAnimationFactory

/**
* A {@link TransitionFactory} that produces {@link ViewTransition}s.
*
* @param <R> The type of the resource that will be transitioned into a view.
*/
public class ViewAnimationFactory<R> implements TransitionFactory<R> {
。。。

一个生成视图转换的TransitionFactory。
类型参数:
R -将被转换到视图的资源的类型。

ViewPropertyAnimationFactory

/**
* A {@link TransitionFactory} that produces ViewPropertyAnimations.
*
* @param <R> The type of the resource that will be transitioned into a view.
*/
public class ViewPropertyAnimationFactory<R> implements TransitionFactory<R> {

一个生成ViewPropertyAnimations的TransitionFactory。
类型参数:
R -将被转换到视图的资源的类型。

小计

在Glide里比较通用的工厂模式结构使用形式，看完前几篇这篇也很容易理解意图

更多

单例模式
Glide设计模式之单例模式
空对象模式
Glide设计模式之空对象模式【EmptyModelLoader】【EmptyList＜E＞
建造者模式
Glide多种组合使用方式记录–没有全部亲测，大家可以根据实际需要选用
Glide设计模式之建造者（builder）模式1【GlideBuilder】
Glide设计模式之建造者（builder）模式2【RequestBuilder】
Glide设计模式之建造者（builder）模式3【RequestOptions】【BaseRequestOptions】
Glide设计模式之建造者（builder）模式4总结【MemorySizeCalculator】【GlideExecutor】【PreFillType】【LazyHeaders】
工厂模式
Glide设计模式之工厂模式1【ModelLoaderFactory】
Glide设计模式之工厂模式2【DiskCache.Factory】
Glide工厂模式3【TransitionFactory】【Transition】
Glide设计模式之工厂模式4总结

最后

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