提问



我很难弄清楚如何在没有用户干预的情况下以编程方式检索相机胶卷中的最新照片。为了清楚起见,我不想使用图像选择器,我希望应用程序自动抓取最新照片时应用打开。


我知道这是可能的,因为我见过类似的应用程序,但我似乎无法找到任何信息。

最佳参考


一种方法是使用AssetsLibrary并使用n - 1作为枚举的索引。


ALAssetsLibrary *assetsLibrary = [**ALAssetsLibrary alloc] init];
[assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
                             usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
                                 if (nil != group) {
                                     // be sure to filter the group so you only get photos
                                     [group setAssetsFilter:[ALAssetsFilter allPhotos**];

                                     if (group.numberOfAssets > 0) {
                                         [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:group.numberOfAssets - 1]
                                                                 options:0
                                                              usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                                                                  if (nil != result) {
                                                                      ALAssetRepresentation *repr = [result defaultRepresentation];
                                                                      // this is the most recent saved photo
                                                                      UIImage *img = [UIImage imageWithCGImage:[repr fullResolutionImage**];
                                                                      // we only need the first (most recent) photo -- stop the enumeration
                                                                      *stop = YES;
                                                                  }
                                                              }];
                                     }
                                 }

                                 *stop = NO;
                             } failureBlock:^(NSError *error) {
                                 NSLog(@"error: %@", error);
                             }];

其它参考1


您可以反过来列出列表,而不是弄乱索引。如果您想要最新的图像,或者您希望首先使用最新图像在UICollectionView中列出图像,则此模式很有效。


返回最新图像的示例:


[group enumerateAssetsWithOptions:NSEnumerationReverse usingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop) {
    if (asset) {
        ALAssetRepresentation *repr = [asset defaultRepresentation];
        UIImage *img = [UIImage imageWithCGImage:[repr fullResolutionImage**];
        *stop = YES;
    }
}];

其它参考2


在iOS 8中,Apple添加了Photos库,以便于查询。在iOS 9中,ALAssetLibrary已被弃用。[13] [14]


这里有一些Swift代码可以获得最近用该框架拍摄的照片。


import UIKit
import Photos

struct LastPhotoRetriever {
    func queryLastPhoto(resizeTo size: CGSize?, queryCallback: (UIImage? -> Void)) {
        let fetchOptions = PHFetchOptions()
        fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]

//        fetchOptions.fetchLimit = 1 // This is available in iOS 9.

        if let fetchResult = PHAsset.fetchAssetsWithMediaType(PHAssetMediaType.Image, options: fetchOptions) {
            if let asset = fetchResult.firstObject as? PHAsset {
                let manager = PHImageManager.defaultManager()

                // If you already know how you want to resize, 
                // great, otherwise, use full-size.
                let targetSize = size == nil ? CGSize(width: asset.pixelWidth, height: asset.pixelHeight) : size!

                // I arbitrarily chose AspectFit here. AspectFill is 
                // also available.
                manager.requestImageForAsset(asset,
                    targetSize: targetSize,
                    contentMode: .AspectFit,
                    options: nil,
                    resultHandler: { image, info in

                    queryCallback(image)
                })
            }
        }
    }
}

其它参考3


要添加到Art Gillespie的答案,使用fullResolutionImage会使用原始图像 - 根据拍摄照片时设备的方向 - 可能会让您倒置或-90°图像。


要获得修改后的优化图像,请使用fullScreenImage代替....


 UIImage *img = [UIImage imageWithCGImage:[repr fullScreenImage**];

其它参考4


Swift 3.0:


1)在类声明之前在标题中导入Photos框架。


import Photos



2)添加以下方法,返回最后一个图像。


func queryLastPhoto(resizeTo size: CGSize?, queryCallback: @escaping ((UIImage?) -> Void)) {
    let fetchOptions = PHFetchOptions()
    fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]

    let requestOptions = PHImageRequestOptions()
    requestOptions.isSynchronous = true

    let fetchResult = PHAsset.fetchAssets(with: PHAssetMediaType.image, options: fetchOptions)
    if let asset = fetchResult.firstObject {
        let manager = PHImageManager.default()

        let targetSize = size == nil ? CGSize(width: asset.pixelWidth, height: asset.pixelHeight) : size!

        manager.requestImage(for: asset,
                             targetSize: targetSize,
                             contentMode: .aspectFit,
                             options: requestOptions,
                             resultHandler: { image, info in
                                queryCallback(image)
        })
    }

}


点击
3)然后在你的应用程序中的某个地方调用此方法(可能是按钮操作):


@IBAction func pressedLastPictureAttachmentButton(_ sender: Any) {
    queryLastPhoto(resizeTo: nil){
        image in
        print(image)
    }
}

其它参考5


回答问题(在 Swift 中):


    func pickingTheLastImageFromThePhotoLibrary() {
        let assetsLibrary: ALAssetsLibrary = ALAssetsLibrary()
        assetsLibrary.enumerateGroupsWithTypes(ALAssetsGroupSavedPhotos,
            usingBlock: { (let group: ALAssetsGroup!, var stop: UnsafeMutablePointer<ObjCBool>) -> Void in
                if (group != nil) {
                    // Be sure to filter the group so you only get photos
                    group.setAssetsFilter(ALAssetsFilter.allPhotos())

                    group.enumerateAssetsWithOptions(NSEnumerationOptions.Reverse, 
                                 usingBlock: { (let asset: ALAsset!, 
                                                let index: Int, 
                                       var stop: UnsafeMutablePointer<ObjCBool>)
                                       -> Void in
                      if(asset != nil) {
                        /* 
                            Returns a CGImage representation of the asset.
                            Using the fullResolutionImage uses the original image which — depending on the
                            device's orientation when taking the photo — could leave you with an upside down,
                            or -90° image. To get the modified, but optimised image for this, use
                            fullScreenImage instead.
                        */
                        // let myCGImage: CGImage! = asset.defaultRepresentation().fullResolutionImage().takeUnretainedValue()

                        /*
                            Returns a CGImage of the representation that is appropriate for displaying full
                            screen.
                        */
                        // let myCGImage: CGImage! = asset.defaultRepresentation().fullScreenImage().takeUnretainedValue()

                        /* Returns a thumbnail representation of the asset. */
                        let myCGImage: CGImage! = asset.thumbnail().takeUnretainedValue()

                        // Here we set the image included in the UIImageView
                        self.myUIImageView.image = UIImage(CGImage: myCGImage)

                        stop.memory = ObjCBool(true)
                      }
                    })
                }

                stop.memory = ObjCBool(false)
            })
            { (let error: NSError!) -> Void in
                 println("A problem occurred: \(error.localizedDescription)")
            }
    }

其它参考6


使用照片库(Objective-C)


    PHFetchOptions *fetchOptions = [**PHFetchOptions alloc] init];
fetchOptions.sortDescriptors = @[**NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:NO**];

PHFetchResult *assetsFetchResult = [PHAsset fetchAssetsInAssetCollection:assetCollection options:fetchOptions];
if (assetsFetchResult.count>0) {
    PHAsset *asset = [assetsFetchResult objectAtIndex:0];

    CGFloat scale = [UIScreen mainScreen].scale;
    CGFloat dimension = 55.0f; // set your required size
    CGSize size = CGSizeMake(dimension*scale, dimension*scale);

    [**PHImageManager defaultManager] requestImageForAsset:asset
                                               targetSize:size
                                              contentMode:PHImageContentModeAspectFit
                                                  options:nil
                                            resultHandler:^(UIImage *result, NSDictionary *info) {
                                                // do your thing with the image
                                            }
     ];
}