PhotoKit框架介绍及使用

　　PhotoKit 是一套比 AssetsLibrary 更新更完整也更高效的ios照片处理库，对资源的处理跟 AssetsLibrary 有很大的不同。下面简单介绍下PhotoKit的几个基本概念

PHAsset：代表照片库中的特定资源，PHAsset对象来表示存储在照片应用程序中或云端的一个图片或视频文件。为了显示或编辑asset，我们需要使用PHAsset类的获取asset来处理它，一个asset对象是不可变的，只包含它所代表的照片或视频的元数据。

[b]PHFetchOptions：[/b]使用PHFetchOptions对象来指定选项，在PHAsset, PHCollection, PHAssetCollection, and PHCollectionList上根据它的对象来检索照片符合要求的实体。我们可以根据一些key来对要显示的照片进行排序。下面是支持的key


PHFetchResult: 表示一系列的资源集合，也可以是相册的集合。它是一个有序的存储照片实体的容器。它是一个泛型集合

PHAssetCollection: 表示一个相册

PHImageManager: 用于处理资源的加载，加载图片的过程带有缓存处理，可以通过传入一个 PHImageRequestOptions 控制资源的输出尺寸等规格

PHImageRequestOptions: 控制加载图片时的一系列参数

下面详细介绍库的使用

我们需要导入Photos.framework

1.PHPhotoLibrary：表示用户的照片库，包括对象存储在本地设备和（如果已启用）在iCloud照片。我们使用PHPhotoLibrary来对照片库进行操作。可以添加编辑删除。

例如使用PHPhotoLibrary来实现拍照功能。

[_mCamera capturePhotoAsJPEGProcessedUpToFilter:_mFilter withCompletionHandler:^(NSData *processedJPEG, NSError *error){

[[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{

[[PHAssetCreationRequest creationRequestForAsset] addResourceWithType:PHAssetResourceTypePhoto data:processedJPEG options:nil];

} completionHandler:^(BOOL success, NSError * _Nullable error) {

}];

}];

2.PHAssetChangeRequest，PHAssetCollectionChangeRequest，PHAssetCreationRequest，PHCollectionListChangeRequest：你可以在PHPhotoLibrary的change block中创建一个它们的对象来对asset对象进行添加，编辑，删除

在上面那段代码中我们展现了PHAssetCreationRequest的添加操作。

[[PHAssetCreationRequest creationRequestForAsset] addResourceWithType:PHAssetResourceTypePhoto data:processedJPEG options:nil];

3.PHAssetCollectionType相册类型

typedef NS_ENUM(NSInteger, PHAssetCollectionType) {
PHAssetCollectionTypeAlbum      = 1,
PHAssetCollectionTypeSmartAlbum = 2,
PHAssetCollectionTypeMoment     = 3,
} NS_ENUM_AVAILABLE_IOS(8_0);

[PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil]

输出：

2016-09-29 15:27:59.392 FWLifeApp[1040:36950] Favorites

2016-09-29 15:27:59.394 FWLifeApp[1040:36950] Recently Deleted

2016-09-29 15:27:59.394 FWLifeApp[1040:36950] Panoramas

2016-09-29 15:27:59.394 FWLifeApp[1040:36950] Camera Roll

2016-09-29 15:27:59.396 FWLifeApp[1040:36950] Slo-mo

2016-09-29 15:27:59.396 FWLifeApp[1040:36950] Screenshots

2016-09-29 15:27:59.397 FWLifeApp[1040:36950] Bursts

2016-09-29 15:27:59.398 FWLifeApp[1040:36950] Videos

2016-09-29 15:27:59.398 FWLifeApp[1040:36950] Selfies

2016-09-29 15:27:59.399 FWLifeApp[1040:36950] Hidden

2016-09-29 15:27:59.400 FWLifeApp[1040:36950] Time-lapse

2016-09-29 15:27:59.400 FWLifeApp[1040:36950] Recently Added

我们可以看出PHAssetCollectionTypeSmartAlbum包含许多相册集。收藏，最近删除，最近添加，相机胶卷等，而不包含时刻.

NSMutableArray<FWPhotoAlbums *> *mArr = [NSMutableArray array];
PHFetchResult *smartAlbum = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
[smartAlbum enumerateObjectsUsingBlock:^(PHAssetCollection *  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
//过滤掉最近删除的，和视频
if (obj.assetCollectionSubtype != 202 && obj.assetCollectionSubtype < 212) {
NSArray <PHAsset *> *assets = [self getAssetsInAssetCollection:obj ascending:NO];
if ([assets count]) {
FWPhotoAlbums *pa = [[FWPhotoAlbums alloc] init];
pa.albumName = [self TitleOfAlbumForChinse:obj.localizedTitle];
pa.albumImageCount = [assets count];
pa.firstImageAsset = assets.firstObject;
pa.assetCollection = obj;
[mArr addObject:pa];
}
}
}];

我们需要进一步获取每个相册集下的所有照片。对照片的creationDate key进行排序

- (PHFetchResult *)fetchAssetsInAssetCollection:(PHAssetCollection *)assetCollection ascending:(BOOL)ascending
{
PHFetchOptions *options = [[PHFetchOptions alloc] init];
options.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:ascending]];
PHFetchResult *result = [PHAsset fetchAssetsInAssetCollection:assetCollection options:options];

return result;
}

- (NSArray <PHAsset *> *)getAssetsInAssetCollection:(PHAssetCollection *)assetCollection ascending:(BOOL)ascending
{
NSMutableArray <PHAsset *> *mArr = [NSMutableArray array];
PHFetchResult *result = [self fetchAssetsInAssetCollection:assetCollection ascending:ascending];
[result enumerateObjectsUsingBlock:^(PHAsset *  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
if (obj.mediaType == PHAssetMediaTypeImage) {
[mArr addObject:obj];
}
}];

return mArr;
}

获取图片

- (void)requestImageForAsset:(PHAsset *)asset size:(CGSize)size resizeMode:(PHImageRequestOptionsResizeMode)resizeMode completion:(void (^)(UIImage *, NSDictionary *))completion
{
static PHImageRequestID requestID = -1;
CGFloat scale = [UIScreen mainScreen].scale;
CGFloat width = MIN(WIDTH, 800);
if (requestID >= 1 && size.width/width==scale) {
[[PHCachingImageManager defaultManager] cancelImageRequest:requestID];
}

PHImageRequestOptions *option = [[PHImageRequestOptions alloc] init];
option.resizeMode = resizeMode;
option.networkAccessAllowed = YES;

requestID = [[PHCachingImageManager defaultManager] requestImageForAsset:asset targetSize:size contentMode:PHImageContentModeAspectFill options:option resultHandler:^(UIImage * _Nullable image, NSDictionary * _Nullable info) {
BOOL downloadFinined = ![[info objectForKey:PHImageCancelledKey] boolValue] && ![info objectForKey:PHImageErrorKey];
if (downloadFinined && completion) {
completion(image, info);
}
}];
}