iOS8之后，苹果推出了PhotoKit，让开发者在处理相册相关的业务时，可以更加得心应手。github上的开发者针对PhotoKit做了一层很优秀的封装CTAssetsPickerController，如果只需要支持iOS8+，那么可定制程度非常高的CTAssetsPickerController是个不错的选择。
但是由于现有的业务还是需要支持iOS7，所以并不能完全舍弃使用AssetsLibrary的方式来访问相册。因此也就需要自己封装一套兼容iOS7的相册管理器。
本文涉及代码：TBVAssetsPicker
统一asset以及collection
| AssetsLibrary | PhotoKit |
|---|---|
| ALAssetsGroup | PHAssetCollection |
| ALAsset | PHAsset |
| TBVAsset | TBVCollection |
相片选择器最终需要向外部提供统一的标识相片的结构。同样，统一结构能让相片选择器更加优雅地实现内部逻辑。所以这里我声明了两个对应的类：TBVAsset、TBVCollection，并提供一些最基本的功能。
@interface TBVAsset : NSObject
/**
* PHAsset or ALAsset
*/
@property (strong, nonatomic) NSObject *asset;
+ (instancetype)assetWithOriginAsset:(NSObject *)asset;
/** 本地标识 */
- (NSString *)assetLocalIdentifer;
/** 源照片尺寸 */
- (CGSize)assetPixelSize;
@end
@interface TBVCollection : NSObject
/**
* ALAssetsGroup or PHAssetCollection
*/
@property (strong, nonatomic) NSObject *collection;
+ (instancetype)collectionWithOriginCollection:(NSObject *)aCollection;
/** 相簿名 */
- (NSString *)collectionTitle;
/** 估算的相簿相片个数 */
- (NSInteger)collectionEstimatedAssetCount;
/** 精确的相簿相片个数 */
- (NSInteger)collectionAccurateAssetCountWithFetchOptions:(id)filterOptions;
- (NSInteger)collectionAccurateAssetCountWithMediaType:(TBVAssetsPickerMediaType)mediaType;
@end
有了这些最基本的功能，在实现相册选择器时，就可以方便地对资源进行操作了。
其实对于这部分的兼容处理，主要就是对两个不同的库进行封装，使其呈现同样的外观，后续的几步大体也是围绕这个目标进行。
封装manager
由于是两个不同版本的库，并且AssetsLibrary已经在iOS9时被弃用，使用时会产生deprecated警告，所以我分别对ALAssetsLibrary和PHCachingImageManager进行了封装，然后通过统一的接口TBVAssetsManagerProtocol暴露其功能。
一般相册选择器具有如下页面及对应功能（UI展示）：
- 首页
- 相簿名
- 相簿缩略图
- 相簿拥有相片数
- 预览页
- 相片缩略图
- 选中相片大小
- 浏览页
- 相片大图
- 选中相片大小
所以我提供的接口如下：
//====================================
// image
//====================================
/** requestImage返回都是一个RACTuple，first是Image，second是是否为degraded */
/** 请求特定大小的图片 */
- (RACSignal *)requestImageForAsset:(TBVAsset *)asset
targetSize:(CGSize)targetSize
contentMode:(TBVAssetsPickerContentMode)contentMode;
/** 请求相簿缩略图 */
- (RACSignal *)requestPosterImageForCollection:(TBVCollection *)collection
mediaType:(TBVAssetsPickerMediaType)mediaType;
/** 请求相片缩略图 */
- (RACSignal *)requestPosterImageForAsset:(TBVAsset *)asset;
/** 请求相片原图 */
- (RACSignal *)requestFullResolutionImageForAsset:(TBVAsset *)asset;
//====================================
// asset / collection
//====================================
/** 请求相片资源大小 */
- (RACSignal *)requestSizeForAssets:(NSArray <TBVAsset *> *)assets;
/** 请求所有相簿 */
- (RACSignal *)requestAllCollections;
/** 请求所有相片资源 */
- (RACSignal *)requestAssetsForCollection:(TBVCollection *)collection
mediaType:(TBVAssetsPickerMediaType)mediaType;
/** 请求相机胶卷相簿（针对一般业务首先进入相机胶卷的预览页） */
- (RACSignal *)requestCameraRollCollection;
//====================================
// video
//====================================
/** 请求AVPlayerItem */
- (RACSignal *)requestVideoForAsset:(TBVAsset *)asset;
/** 请求AVURLAsset */
- (RACSignal *)requestURLAssetForAsset:(TBVAsset *)asset;
实现以上接口，一般相册选择器的功能点就已经完成大半了。
TBVAssetsPickerManager
由于自定义的相册manager都遵守TBVAssetsManagerProtocol，TBVAssetsPickerManager
的实现就变得相对简单，没有一大串令人厌烦的if-else。当然TBVAssetsPickerManager本身也是遵守TBVAssetsManagerProtocol的。
@interface TBVAssetsPickerManager()
@property (strong, nonatomic) NSObject<TBVAssetsManagerProtocol> *realManager;
@property (strong, nonatomic) NSMutableArray *requestIdList;
@property (assign, nonatomic) BOOL photoKitAvailable;
@end
#pragma mark life cycle
- (instancetype)init {
self = [super init];
if (self) {
_photoKitAvailable = NSClassFromString(@"PHImageManager") != nil;
}
return self;
}
#pragma mark TBVAssetsManagerProtocol
....
#pragma mark getter setter
- (NSObject *)realManager
{
if (_realManager == nil) {
if (self.photoKitAvailable) {
_realManager = [[TBVCachingImageManager alloc] init];
} else {
_realManager = [[TBVAssetsLibrary alloc] init];
}
}
return _realManager;
}
这样_realManager拿到的就是当前版本最新的相册manager了。
接口的实现
其实接口文档描述的还是非常清晰的，所以这里只是罗列了下代码，并没有针对每一步做解释，因为这些基本的操作进去头文件看看就全明白了。
- requestImageForAsset:targetSize:(CGSize)targetSize:contentMode:
这个接口主要用来获取非原图。
- TBVCachingImageManager
- 关于PHImageRequestOptions的deliveryMode，
- 设置为PHImageRequestOptionsDeliveryModeOpportunistic并且synchronous为NO时，请求可能会先返回一张缩略图，然后再返回一张大图，这个可以通过获取请求回调字典中PHImageResultIsDegradedKey对应value来判别
- PHImageRequestOptionsDeliveryModeHighQualityFormat和PHImageRequestOptionsDeliveryModeFastFormat都返回一张图片，只不过前者返回的图片的质量高于或等于请求的质量，而后者可能返回一张质量稍低的图片
- 关于PHImageRequestOptions的deliveryMode，
- TBVAssetsLibrary
- 由于AssetsLibrary并没有提供获取特定尺寸的相片接口，所以这里只是返回thumbnail、aspectRatioThumbnail、fullScreenImage中尺寸和目标大小最接近的一张图片。
// TBVCachingImageManager
- (RACSignal *)requestImageForAsset:(TBVAsset *)asset
targetSize:(CGSize)targetSize
contentMode:(TBVAssetsPickerContentMode)contentMode {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
PHImageRequestID requestId = [self.imageManager
requestImageForAsset:(PHAsset *)asset.asset
targetSize:targetSize
contentMode:[self contentModeForCustomContentMode:contentMode]
options:self.defaultImageRequestOptions
resultHandler:^(UIImage * _Nullable result,
NSDictionary * _Nullable info) {
[subscriber sendNext:RACTuplePack(result, info[PHImageResultIsDegradedKey])];
if (![info[PHImageResultIsDegradedKey] boolValue]) {
[subscriber sendCompleted];
}
}];
return [RACDisposable disposableWithBlock:^{
[self.imageManager cancelImageRequest:requestId];
}];
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestImageForAsset:(TBVAsset *)aAsset
targetSize:(CGSize)targetSize
contentMode:(TBVAssetsPickerContentMode)contentMode {
return [[[RACSignal return:aAsset.asset]
deliverOn:[RACScheduler scheduler]]
map:^id(ALAsset * asset) {
CGImageRef resultImageRef = nil;
BOOL degraded = NO;
if (targetSize.width < CGImageGetWidth(asset.thumbnail) &&
targetSize.height < CGImageGetHeight(asset.thumbnail)) {
// TBVAssetsPickerContentModeFill
resultImageRef = asset.thumbnail;
degraded = YES;
}
if (!resultImageRef) {
CGImageRef aspectRatioThumbnail = asset.aspectRatioThumbnail;
if (targetSize.width < CGImageGetWidth(aspectRatioThumbnail) &&
targetSize.height < CGImageGetHeight(aspectRatioThumbnail)) {
// TBVAssetsPickerContentModeFit
resultImageRef = aspectRatioThumbnail;
}
if (!resultImageRef) {
ALAssetRepresentation *assetRepresentation = [asset defaultRepresentation];
resultImageRef = [assetRepresentation fullScreenImage];
}
}
UIImage *resultImage = nil;
if (resultImageRef) {
resultImage = [UIImage imageWithCGImage:resultImageRef
scale:BQAP_SCREEN_SCALE
orientation:UIImageOrientationUp];
}
return RACTuplePack(resultImage, @(degraded));
}];
}
-requestPosterImageForCollection:mediaType:
- TBVCachingImageManager
- 通过-fetchKeyAssetsInAssetCollection:options:获取相簿keyAssets，最多可以返回三个
- 最终还是通过requestPosterImageForAsset:获取缩略图
- 获取keyAssets前，需要设置options对资源进行过滤：
+ (instancetype)tbv_fetchOptionsWithCustomMediaType:(TBVAssetsPickerMediaType)mediaType {
NSArray *mediaTypes = [self tbv_mediaTypesWithCustonMediaType:mediaType];
if (!mediaTypes.count) return nil;
PHFetchOptions *options = [[PHFetchOptions alloc] init];
NSMutableString *predicateString = [NSMutableString string];
for (NSNumber *mediaType in mediaTypes) {
[predicateString appendFormat:@"mediaType = %@", mediaType];
if (![mediaType isEqual:mediaTypes.lastObject]) [predicateString appendString:@" || "];
}
options.predicate = [NSPredicate predicateWithFormat:predicateString];
return options;
}
- TBVAssetsLibrary
- ALAssetsGroup有posterImage属性，直接返回相簿缩略图
- 和PhotoKit不同，AssetLibrary通过ALAssetsGroup的setAssetsFilter方法进行过滤
[group setAssetsFilter:[ALAssetsFilter tbv_assetsFilterWithCustomMediaType:mediaType]];
这样设置以后，后续针对group的操作都会在过滤的结果中进行了。
// TBVCachingImageManager
- (RACSignal *)requestPosterImageForCollection:(TBVCollection *)collection
mediaType:(TBVAssetsPickerMediaType)mediaType {
return [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
PHFetchOptions *fetchOptions = [PHFetchOptions tbv_fetchOptionsWithCustomMediaType:mediaType];
fetchOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate"
ascending:YES]];
PHAssetCollection *realCollection = (PHAssetCollection *)collection.collection;
/* fetchKeyAssetsInAssetCollection 获取至多三张 */
PHFetchResult *result = [PHAsset fetchKeyAssetsInAssetCollection:realCollection
options:fetchOptions];
if (!result.count) {
[subscriber sendNext:[RACSignal empty]];
[subscriber sendCompleted];
return nil;
}
TBVAsset *posterAsset = [TBVAsset assetWithOriginAsset:result.firstObject];
[subscriber sendNext:[self requestPosterImageForAsset:posterAsset]];
[subscriber sendCompleted];
return nil;
}] switchToLatest];
}
// TBVAssetsLibrary
- (RACSignal *)requestAssetsForCollection:(TBVCollection *)collection
mediaType:(TBVAssetsPickerMediaType)mediaType {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSMutableArray *assets = [NSMutableArray array];
ALAssetsGroup *group = (ALAssetsGroup *)collection.collection;
[group setAssetsFilter:[ALAssetsFilter tbv_assetsFilterWithCustomMediaType:mediaType]];
[group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
if (result) {
[assets addObject:[TBVAsset assetWithOriginAsset:result]];
} else {
[subscriber sendNext:assets];
[subscriber sendCompleted];
}
}];
return nil;
}];
}
-requestPosterImageForAsset:
获取asset的缩略图，需要注意的一点就是：在获取缩略图的情况下，Fill比Fit获取的图片要清晰
// TBVCachingImageManager
- (RACSignal *)requestPosterImageForAsset:(TBVAsset *)asset {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
CGSize posterSize = CGSizeMake(kBQPosterImageWidth * BQAP_SCREEN_SCALE,
kBQPosterImageHeight * BQAP_SCREEN_SCALE);
/* 在获取缩略图的情况下，Fill比Fit获取的图片要清晰 */
PHImageRequestID requestId = [self.imageManager
requestImageForAsset:(PHAsset *)asset.asset
targetSize:posterSize
contentMode:PHImageContentModeAspectFill
options:self.defaultImageRequestOptions
resultHandler:^(UIImage * _Nullable result,
NSDictionary * _Nullable info) {
[subscriber sendNext:RACTuplePack(result, info[PHImageResultIsDegradedKey])];
if (![info[PHImageResultIsDegradedKey] boolValue]) {
[subscriber sendCompleted];
}
}];
return [RACDisposable disposableWithBlock:^{
[self.imageManager cancelImageRequest:requestId];
}];
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestPosterImageForAsset:(TBVAsset *)asset {
return [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
CGSize posterSize = CGSizeMake(kBQPosterImageWidth * BQAP_SCREEN_SCALE,
kBQPosterImageHeight * BQAP_SCREEN_SCALE);
[subscriber sendNext:[self requestImageForAsset:asset
targetSize:posterSize
contentMode:TBVAssetsPickerContentModeFill]];
[subscriber sendCompleted];
return nil;
}] switchToLatest];
}
-requestFullResolutionImageForAsset:
获取原图时有一点很重要，就是尽量不要快速连续地获取原图，大图也可以列入这个范畴。连续地获取大图或者原图，设备的内存会急剧增高，甚至崩溃，这种情况通常在上传图片时比较常见。
所以在上传图片时，尽量上传一张原图后再获取下一张原图进行上传，而不是全部获取完成之后再上传。
// TBVCachingImageManager
- (RACSignal *)requestFullResolutionImageForAsset:(TBVAsset *)asset {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
self.defaultImageRequestOptions.networkAccessAllowed = YES;
PHImageRequestID requestId = [self.imageManager
requestImageForAsset:(PHAsset *)asset.asset
targetSize:PHImageManagerMaximumSize
contentMode:PHImageContentModeDefault
options:self.defaultImageRequestOptions
resultHandler:^(UIImage * _Nullable result,
NSDictionary * _Nullable info) {
[subscriber sendNext:RACTuplePack(result, info[PHImageResultIsDegradedKey])];
if (![info[PHImageResultIsDegradedKey] boolValue]) {
[subscriber sendCompleted];
}
}];
return [RACDisposable disposableWithBlock:^{
[self.imageManager cancelImageRequest:requestId];
}];
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestFullResolutionImageForAsset:(TBVAsset *)asset {
return [[[RACSignal return:asset.asset]
deliverOn:[RACScheduler scheduler]]
map:^id(ALAsset * asset) {
ALAssetRepresentation *assetRepresentation = [asset defaultRepresentation];
CGImageRef fullResolutionImage = [assetRepresentation fullResolutionImage];
UIImage *resultImage = [UIImage imageWithCGImage:fullResolutionImage
scale:BQAP_SCREEN_SCALE
orientation:UIImageOrientationUp];
return RACTuplePack(resultImage, @(NO));
}];
}
-requestSizeForAssets:
请求大小是针对的图片，所以对非图片的asset进行了过滤
// TBVCachingImageManager
- (RACSignal *)requestSizeForAssets:(NSArray<TBVAsset *> *)assets {
RACSequence *requestSequence = [[assets.rac_sequence
filter:^BOOL(TBVAsset *asset) {
return ((PHAsset *)asset.asset).mediaType == PHAssetMediaTypeImage;
}]
map:^id(TBVAsset *asset) {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
self.defaultImageRequestOptions.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;
PHImageRequestID requestId =[self.imageManager
requestImageDataForAsset:(PHAsset *)asset.asset
options:self.defaultImageRequestOptions
resultHandler:^(NSData * _Nullable imageData,
NSString * _Nullable dataUTI,
UIImageOrientation orientation,
NSDictionary * _Nullable info) {
[subscriber sendNext:@(imageData.length)];
[subscriber sendCompleted];
}];
return [RACDisposable disposableWithBlock:^{
[self.imageManager cancelImageRequest:requestId];
}];
}];
}];
return [[RACSignal
zip:requestSequence]
map:^id(RACTuple *value) {
return [value.rac_sequence foldLeftWithStart:@0 reduce:^id(id accumulator, id value) {
return @([accumulator integerValue] + [value integerValue]);
}];
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestSizeForAssets:(NSArray<TBVAsset *> *)assets {
return [RACSignal
return:[[[[assets.rac_sequence
map:^id(TBVAsset *asset) {
return asset.asset;
}]
filter:^BOOL(ALAsset *asset) {
return [asset valueForProperty:ALAssetPropertyType] == ALAssetTypePhoto;
}]
map:^id(ALAsset *asset) {
return @([asset defaultRepresentation].size);
}]
foldLeftWithStart:@(0) reduce:^id(id accumulator, id value) {
return @([accumulator integerValue] + [value integerValue]);
}]];
}
-requestAllCollections
// TBVCachingImageManager
- (RACSignal *)requestAllCollections {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
PHFetchResult *smartResult = [PHAssetCollection
fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum
subtype:PHAssetCollectionSubtypeAlbumRegular
options:nil];
PHFetchResult *topLevelUserCollections = [PHCollectionList fetchTopLevelUserCollectionsWithOptions:nil];
NSMutableArray *collections = [NSMutableArray array];
for (PHAssetCollection *aCollection in smartResult) {
TBVCollection *collection = [TBVCollection collectionWithOriginCollection:aCollection];
[collections addObject:collection];
}
for (PHAssetCollection *aCollection in topLevelUserCollections) {
TBVCollection *collection = [TBVCollection collectionWithOriginCollection:aCollection];
[collections addObject:collection];
}
[subscriber sendNext:collections];
[subscriber sendCompleted];
return nil;
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestAllCollections {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSMutableArray *collections = [NSMutableArray array];
[self.assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAll
usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
if (group) {
TBVCollection *collection = [TBVCollection collectionWithOriginCollection:group];
[collections addObject:collection];
} else {
[subscriber sendNext:collections];
[subscriber sendCompleted];
}
} failureBlock:^(NSError *error) {
[subscriber sendError:error];
}];
return nil;
}];
}
-requestAssetsForCollection:mediaType:
// TBVCachingImageManager
- (RACSignal *)requestAssetsForCollection:(TBVCollection *)collection
mediaType:(TBVAssetsPickerMediaType)mediaType {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
PHFetchOptions *options = [PHFetchOptions tbv_fetchOptionsWithCustomMediaType:mediaType];
PHFetchResult *fetchResult = [PHAsset fetchAssetsInAssetCollection:(PHAssetCollection *)collection.collection
options:options];
NSMutableArray *assets = [NSMutableArray arrayWithCapacity:fetchResult.count];
for (PHAsset *asset in fetchResult) {
[assets addObject:[TBVAsset assetWithOriginAsset:asset]];
}
[subscriber sendNext:assets];
[subscriber sendCompleted];
return nil;
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestAssetsForCollection:(TBVCollection *)collection
mediaType:(TBVAssetsPickerMediaType)mediaType {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSMutableArray *assets = [NSMutableArray array];
ALAssetsGroup *group = (ALAssetsGroup *)collection.collection;
[group setAssetsFilter:[ALAssetsFilter tbv_assetsFilterWithCustomMediaType:mediaType]];
[group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
if (result) {
[assets addObject:[TBVAsset assetWithOriginAsset:result]];
} else {
[subscriber sendNext:assets];
[subscriber sendCompleted];
}
}];
return nil;
}];
}
-requestCameraRollCollection
// TBVCachingImageManager
- (RACSignal *)requestCameraRollCollection {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
PHFetchResult *smartAlbums = [PHAssetCollection
fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum
subtype:PHAssetCollectionSubtypeSmartAlbumUserLibrary
options:nil];
[subscriber sendNext:[TBVCollection collectionWithOriginCollection:smartAlbums.firstObject]];
[subscriber sendCompleted];
return nil;
}];
}
// TBVAssetsLibrary
- (RACSignal *)requestCameraRollCollection {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[self.assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
[subscriber sendNext:[TBVCollection collectionWithOriginCollection:group]];
[subscriber sendCompleted];
} failureBlock:^(NSError *error) {
[subscriber sendError:error];
}];
return nil;
}];
}
-requestVideoForAsset:和-requestURLAssetForAsset:
由于业务上没有视频的需求，所以这一块还没有去实现。
实现过程中的一些小坑
用ALAssetsLibrary申请访问相册权限
这一点貌似有些代码用authorizationStatus就能实现，不过
应用的时候还是发现不能触发请求权限alert，所以这里需要访问下相册的资源ask-permission-to-access-camera-roll，
来触发这个请求动作：
+ (RACSignal *)tbv_forceTriggerPermissionAsking {
return [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
void (^sendStatus)() = ^{
[subscriber sendNext:@([self tbv_authorizationStatus])];
[subscriber sendCompleted];
};
if ([self tbv_authorizationStatus] != BQAuthorizationStatusNotDetermined) {
sendStatus();
return nil;
}
ALAssetsLibrary *lib = [[ALAssetsLibrary alloc] init];
[lib enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
sendStatus();
*stop = YES;
} failureBlock:^(NSError *error) {
sendStatus();
}];
return nil;
}] deliverOnMainThread];
}
ALAssetsLibrary请求的ALAsset被置空问题
官方文档里面有这么一句：
The lifetimes of objects you get back from a library instance are tied to the lifetime of the library instance.
可以看到，在使用ALAssetsLibrary请求回来的资源时，是不能释放对应的ALAssetsLibrary对象的。在发送多图的场合，如果不注意保持住ALAssetsLibrary对象，很容易发生后面几张图片获取不到的情况。
所以，要么在选择器返回选中的资源时，强引用对应的manager，要么这个manager由调用者传给相册选择器。
更改应用权限并切回前台
如果应用在后台时，更改了权限，当切回前台后，App会重新启动 。这里如果设置了断点，别以为是程序崩了。
不足
一个很明显的问题是使用了RAC的版本后，相册选择器滚动的性能会下降，没有以前通过回调来的顺畅。如果稍微快速一点滚动的话，CPU很容易就上100%。
可能是使用RAC的方式不是很正确造成的，后续尽可能优化这一块。
