![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsICM38FdsYkRGZkRG9lcvx2bjxiNx8VZ6l2cs0zYtJGa4VlWspFMMBjVtJWd0ckW65UbM5WOHJWa5kHT20ESjBjUIF2X0hXZ0xCMx81dvRWYoNHLrdEZwZ1Rh5WNXp1bwNjW1ZUba9VZwlHdssmch1mclRXY39CXldWYtlWPzNXZj9mcw1ycz9WL49zZuBnLyIzN1ATMyAjM4ITNwkTMwIzLc52YucWbp5GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.png)
使用Fresco之前,一定先要进行初始化,一般初始化的工作会在
Application.onCreate()
完成,当然也可以在使用
Drawee
之前完成。
Fresco本身提供了两种初始化方式,一种是使用使用默认配置初始化,另一种是使用用户自定义配置。
如下代码是Fresco提供的两个初始化方法。第一个只需要提供一个
Context
参数,第二个还需要提供 ImagePipeline 的配置实例 -
ImagePipelineConfig
。
/** Initializes Fresco with the default config. */
public static void initialize(Context context) {
ImagePipelineFactory.initialize(context);
initializeDrawee(context);
}
/** Initializes Fresco with the specified config. */
public static void initialize(Context context, ImagePipelineConfig imagePipelineConfig) {
ImagePipelineFactory.initialize(imagePipelineConfig);
initializeDrawee(context);
}
先来分析一下第一种方式。
开始初始化
Fresco.initialized(context)
使用默认参数进行初始化
com.facebook.drawee.backends.pipeline.Fresco
/** Initializes Fresco with the default config. */
public static void initialize(Context context) {
ImagePipelineFactory.initialize(context);
initializeDrawee(context);
}
其中
ImagePipeline
负责获取图像数据,可以是网络图片,也可以是本地图片。这里用一个 Factory -
ImagePipelineFactory
来创建默认的
ImagePipleline
。
创建 ImagePipeline
com.facebook.imagepipeline.core.ImagePipelineFactory
/** Initializes {@link ImagePipelineFactory} with default config. */
public static void initialize(Context context) {
initialize(ImagePipelineConfig.newBuilder(context).build());
}
ImagePipelineConfig
为
ImagePipeline
的初始化工作提供了必需的参数,它的构建过程采用了Builder模式。
ImagePipelineConfig
中包含了很多参数,因为我们调用
Fresco.initialize()
的时候值传递了一个
context
参数,所以 Fresco 还没有获取任何用户自定义的数据,因此全部使用默认值,
Builder
类只提供了构建的过程,而默认值则需要等到新建
ImagePipelineConfig
时创建。
通过
Builder
的部分源码可以看出,初始化一个
ImagePipeline
需要很多参数,这些参数的具体意义会在后续的博文中介绍。
public static class Builder {
private Supplier<MemoryCacheParams> mBitmapMemoryCacheParamsSupplier;
private CacheKeyFactory mCacheKeyFactory;
private final Context mContext;
private Supplier<MemoryCacheParams> mEncodedMemoryCacheParamsSupplier;
private ExecutorSupplier mExecutorSupplier;
private ImageCacheStatsTracker mImageCacheStatsTracker;
private ImageDecoder mImageDecoder;
private Supplier<Boolean> mIsPrefetchEnabledSupplier;
private DiskCacheConfig mMainDiskCacheConfig;
private MemoryTrimmableRegistry mMemoryTrimmableRegistry;
private NetworkFetcher mNetworkFetcher;
private PoolFactory mPoolFactory;
private ProgressiveJpegConfig mProgressiveJpegConfig;
private Set<RequestListener> mRequestListeners;
private boolean mResizeAndRotateEnabledForNetwork = true;
private DiskCacheConfig mSmallImageDiskCacheConfig;
private AnimatedImageFactory mAnimatedImageFactory;
// other methods
}
从 Fresco 的
initialize
方法中我们得知,
ImagePipelineConfig
是这么创建的:
ImagePipelineConfig.newBuilder(context).build())
而
Builder
并没有提供参数的默认值,那默认值肯定是在
buid()
方法完成赋值。
com.facebook.imagepipeline.core.ImagePipelineFactory$Builder
public ImagePipelineConfig build() {
return new ImagePipelineConfig(this);
}
由以上代码可以看出,
build()
会创建一个
ImagePipelineConfig
,然后把
this
作为参数传给构造函数,而
ImagePipelineConfig
的构造函数就是根据
Builder
来初始化自己。
初始化的策略非常简单:
- 如果
中的参数值为空,则使用默认值。builder
- 如果
中的参数值不为空,则使用builder
提供的值。Builder
可以通过一个具体的参数来看一下,如果
builder.mBitmapMemoryCacheParamsSupplier
为空,则
new DefaultBitmapMemoryCacheParamsSupplier()
,如果不空,则使用
builder.mBitmapMemoryCacheParamsSupplier
。
mBitmapMemoryCacheParamsSupplier =
builder.mBitmapMemoryCacheParamsSupplier == null ?
new DefaultBitmapMemoryCacheParamsSupplier(
(ActivityManager) builder.mContext.getSystemService(Context.ACTIVITY_SERVICE)) :
builder.mBitmapMemoryCacheParamsSupplier;
最后把这个 build 出来的
ImagePipelineConfig
实例传给
ImagePipelineFactory
的静态方法
initialize
,完成初始化。
/** Initializes {@link ImagePipelineFactory} with the specified config. */
public static void initialize(ImagePipelineConfig imagePipelineConfig) {
sInstance = new ImagePipelineFactory(imagePipelineConfig);
}
ImagePipelineFactory
的实例
sInstance
会在初始化 Drawee 的时候用到。
初始化 Drawee
通过以上分析我们了解到,
Fresco
会首先初始化
ImagePipeline
,并把
ImagePipeline
的实例保存在一个
ImagePipelineFactory
类型的静态变量中 -
sInstance
;然后开始初始化
Drawee
。
private static void initializeDrawee(Context context) {
sDraweeControllerBuilderSupplier = new PipelineDraweeControllerBuilderSupplier(context);
SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier);
}
首先,
new
一个
PipelineDraweeControllerBuilderSupplier
,它是
PipelineDraweeControllerBuilder
的一个
Supplier
。
Supplier
不是由 JDK 提供的,而是 Fresco 直接从 guava 中移过来的,代码简单,只提供了一个
get
方法。
/**
* A class that can supply objects of a single type. Semantically, this could
* be a factory, generator, builder, closure, or something else entirely. No
* guarantees are implied by this interface.
*
* @author Harry Heymann
* @since 2.0 (imported from Google Collections Library)
*/
public interface Supplier<T> {
/**
* Retrieves an instance of the appropriate type. The returned object may or
* may not be a new instance, depending on the implementation.
*
* @return an instance of the appropriate type
*/
T get();
}
顾名思义,
Supplier
是一个提供者,用户包括但不限于
factory
,
generator
,
builder
,
closure
,接口方法
get()
用于返回它所提供的实例,需要注意的是,这个实例可以是新建的,也可以不是。
在这里,
PipelineDraweeControllerBuilderSupplier
的用法更像是一个
Factory
,它实现了
Supplier
接口。
public class PipelineDraweeControllerBuilderSupplier implements
Supplier<PipelineDraweeControllerBuilder> {
private final Context mContext;
private final ImagePipeline mImagePipeline;
private final PipelineDraweeControllerFactory mPipelineDraweeControllerFactory;
private final Set<ControllerListener> mBoundControllerListeners;
public PipelineDraweeControllerBuilderSupplier(Context context) {
this(context, ImagePipelineFactory.getInstance());
}
public PipelineDraweeControllerBuilderSupplier(
Context context,
ImagePipelineFactory imagePipelineFactory) {
this(context, imagePipelineFactory, null);
}
public PipelineDraweeControllerBuilderSupplier(
Context context,
ImagePipelineFactory imagePipelineFactory,
Set<ControllerListener> boundControllerListeners) {
mContext = context;
mImagePipeline = imagePipelineFactory.getImagePipeline();
mPipelineDraweeControllerFactory = new PipelineDraweeControllerFactory(
context.getResources(),
DeferredReleaser.getInstance(),
imagePipelineFactory.getAnimatedDrawableFactory(),
UiThreadImmediateExecutorService.getInstance());
mBoundControllerListeners = boundControllerListeners;
}
@Override
public PipelineDraweeControllerBuilder get() {
return new PipelineDraweeControllerBuilder(
mContext,
mPipelineDraweeControllerFactory,
mImagePipeline,
mBoundControllerListeners);
}
}
构造函数
PipelineDraweeControllerBuilderSupplier(Context context)
,使用了在
Fresco
的
initalize
方法中通过
ImagePipelineFactoryBuilder
创建的
ImagePipelineFactory
的实例。
this(context, ImagePipelineFactory.getInstance());
get
方法告诉我们,
ImagePipeline
会存储在
PipelineDraweeController
中,关于
Controller
可以参考 Fresco源码解析 - Hierarachy-View-Controller。
同时
PipelineDraweeController
也会存储一个
mPipelineDraweeControllerFactory
。
public class PipelineDraweeControllerFactory {
private Resources mResources;
private DeferredReleaser mDeferredReleaser;
private AnimatedDrawableFactory mAnimatedDrawableFactory;
private Executor mUiThreadExecutor;
public PipelineDraweeControllerFactory(
Resources resources,
DeferredReleaser deferredReleaser,
AnimatedDrawableFactory animatedDrawableFactory,
Executor uiThreadExecutor) {
mResources = resources;
mDeferredReleaser = deferredReleaser;
mAnimatedDrawableFactory = animatedDrawableFactory;
mUiThreadExecutor = uiThreadExecutor;
}
public PipelineDraweeController newController(
Supplier<DataSource<CloseableReference<CloseableImage>>> dataSourceSupplier,
String id,
Object callerContext) {
return new PipelineDraweeController(
mResources,
mDeferredReleaser,
mAnimatedDrawableFactory,
mUiThreadExecutor,
dataSourceSupplier,
id,
callerContext);
}
}
这个
mPipelineDraweeControllerFactory
会通过
newController
来创建一个
PipelineDraweeController
的实例。
到底,初始化的工作就完成了。
以上分析虽然简单,但是清楚地梳理了 Fresco 的初始化过程,不过任然是远远不够的,由以上代码可以看出,初始化对应组件(Drawee、ImagePipeline)时用到了很多的设计模式,如果不太熟悉这些设计模式,可能理解起来会比较吃力。更加关键的是,初始化对应的组件用到了大量的参数,每个参数背后又会牵扯到很多知识点,后续博文中,我们再来一一分析。