PhotoKit框架介紹及使用

　　PhotoKit 是一套比 AssetsLibrary 更新更完整也更高效的ios照片處理庫，對資源的處理跟 AssetsLibrary 有很大的不同。下麵簡單介紹下PhotoKit的幾個基本概念

• PHAsset：代表照片庫中的特定資源，PHAsset對象來表示存儲在照片應用程式中或雲端的一個圖片或視頻文件。為了顯示或編輯asset，我們需要使用PHAsset類的獲取asset來處理它，一個asset對象是不可變的，只包含它所代表的照片或視頻的元數據。
• PHFetchOptions：使用PHFetchOptions對象來指定選項，在PHAsset, PHCollection, PHAssetCollection, and PHCollectionList上根據它的對象來檢索照片符合要求的實體。我們可以根據一些key來對要顯示的照片進行排序。下麵是支持的key
• PHFetchResult: 表示一系列的資源集合，也可以是相冊的集合。它是一個有序的存儲照片實體的容器。它是一個泛型集合
• PHAssetCollection: 表示一個相冊
• PHImageManager: 用於處理資源的載入，載入圖片的過程帶有緩存處理，可以通過傳入一個 PHImageRequestOptions 控制資源的輸出尺寸等規格
• PHImageRequestOptions: 控制載入圖片時的一系列參數

下麵詳細介紹庫的使用

我們需要導入Photos.framework

1.PHPhotoLibrary：表示用戶的照片庫，包括對象存儲在本地設備和（如果已啟用）在iCloud照片。我們使用PHPhotoLibrary來對照片庫進行操作。可以添加編輯刪除。

例如使用PHPhotoLibrary來實現拍照功能。

    [_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中創建一個它們的對象來對asset對象進行添加，編輯，刪除

在上面那段代碼中我們展現了PHAssetCreationRequest的添加操作。

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

3.PHAssetCollectionType相冊類型

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

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

輸出：

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

我們可以看出PHAssetCollectionTypeSmartAlbum包含許多相冊集。收藏，最近刪除，最近添加，相機膠卷等，而不包含時刻.

NSMutableArray<FWPhotoAlbums *> *mArr = [NSMutableArray array];
    PHFetchResult *smartAlbum = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    [smartAlbum enumerateObjectsUsingBlock:^(PHAssetCollection *  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
//過濾掉最近刪除的，和視頻
        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];
            }
        }
    }];

我們需要進一步獲取每個相冊集下的所有照片。對照片的creationDate key進行排序

- (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;
}

獲取圖片

- (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);
        }
    }];
}