引入头文件#import <Photos/Photos.h>

.h文件，声明方法

/**
 获取相册最近的一张图片
 
 @param screenshot 获取相册最近的一张截屏

 @param imageBlock 得到图片
 */
+ (void)getCurrentImage:(BOOL)screenshot callBack:(void (^)(UIImage *image))imageBlock;

.m文件，实现方法

+ (void)getCurrentImage:(BOOL)screenshot callBack:(void (^)(UIImage *))imageBlock {
    PHAuthorizationStatus status = [PHPhotoLibrary authorizationStatus];
    if (status == PHAuthorizationStatusRestricted || status == PHAuthorizationStatusDenied) {
        NSLog(@"相册权限未开放");
        return;
    }
    // 获取最近的照片
    PHAsset *asset = [[PHAsset fetchAssetsWithOptions:[PHFetchOptions new]] lastObject];
    if (screenshot) {
        // 获取屏幕快照相册
        PHAssetCollection *assetCollection = [[PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeSmartAlbumScreenshots options:nil] firstObject];
        // 获取最近的屏幕快照
        asset = [[PHAsset fetchAssetsInAssetCollection:assetCollection options:[PHFetchOptions new]] lastObject];
    }
    if (!asset) {
        NSLog(@"相册里没有照片");
        return;
    }
    long long now = [[NSDate date] timeIntervalSince1970];
    long long creatTime = [asset.creationDate timeIntervalSince1970];
    if ((now - creatTime) > 86400) {
        NSLog(@"最新的照片是一天以前的");
        return;
    }
    CGSize targetSize = [UIScreen mainScreen].bounds.size;
    NSInteger index = targetSize.width == 414 ? 3 : 2;
    // 将PHAsset *类型的图片转成UIImage *类型
    [[PHCachingImageManager defaultManager] requestImageForAsset:asset targetSize:targetSize contentMode:PHImageContentModeAspectFill options:nil resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
        if (result && result.size.width == targetSize.width * index && result.size.height == targetSize.height * index && imageBlock) {
            imageBlock(result);
        }
    }];
}