如何正确使用带有本地标识符的获取资产？

问题描述

我试图找出如何获取标识符数组并将其以编程方式放入集合视图中的方法。如果我错了，请纠正我，但是，我相信最好的方法是使用PHAsset.fetchAssets。我最多希望用户获取10张图像（平均3-4张），因此我认为该过程不会占用大量资源。我正在用特定的标识符数组测试下面的代码。在分配资产的行的cellForItemAt函数中，我收到一条错误消息。请参阅该行上方的注释。我在SO上看到过类似的问题，但是我无法应用发现的任何内容。我在做什么错了？

var identifier: [String] = ["83BDF9C0-E1FB-4F68-9F2C-99649A67E218/L0/001","18D08CEC-4075-4488-BFD1-E9403B214356/L0/001","74257416-6D9C-48B2-9CE0-C23B56CB4171/L0/001","2EA7CACE-9B9B-4FC9-ABC5-03BCE2BDAA2A/L0/001","46A4CD2B-4FEB-4BBE-86DC-B79ED49BC300/L0/001","E4290EB0-2B16-46AE-9B98-83379F6128F3/L0/001","7C0B36FF-320D-4083-92E4-5A1F464FFFB1/L0/001","DEE1414C-2B92-4147-8C3C-A1775FB324AD/L0/001"]
    
class DetailViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout{
    
    var myCollectionView: UICollectionView!
    let imgManager = PHImageManager.default()
    let requestOptions = PHImageRequestOptions()
    var fetchResult: PHFetchResult<PHAsset>!
    
    override func viewDidLoad() {
        requestOptions.isSynchronous = false
        requestOptions.deliveryMode = .opportunistic
        let layout = UICollectionViewFlowLayout()
        myCollectionView = UICollectionView(frame: self.view.frame,collectionViewLayout: layout)
        myCollectionView.delegate = self
        myCollectionView.dataSource = self
        myCollectionView.backgroundColor = UIColor.white
        myCollectionView.allowsMultipleSelection = true
        myCollectionView.register(ImageEditCell.self,forCellWithReuseIdentifier: "Cell")
        myCollectionView.showsverticalScrollIndicator = false
        self.view.addSubview(myCollectionView)
    }
    func collectionView(_ collectionView: UICollectionView,cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell",for: indexPath) as! ImageEditCell
        cell.representedAssetIdentifier = identifier[0]
        let requestOptions = PHImageRequestOptions()
        requestOptions.isSynchronous = false
        
        // LINE BELOW PRODUCES ERROR: Cannot convert value of type '[String]' to expected element type 'Array<String>.ArrayLiteralElement' (aka 'String')
        let asset = PHAsset.fetchAssets(withLocalIdentifiers: [identifier],options: .none).firstObject
        
        imgManager.requestimage(for: asset!,targetSize: CGSize(width:120,height: 120),contentMode: .aspectFill,options: requestOptions,resultHandler: { result,info in
                                    if cell.representedAssetIdentifier == self.identifier {
                                        cell.imageview.image = result
                                    }
                                })
    }
}

解决方法

在这里，我将获取功能移至viewDidLoad以避免其他错误，而且我不确定要获取的内容是否为包含图像的数组（如果这样，则通过放置.firstObject来获取单个图像，可能会导致错误）

var identifier: [String] = ["83BDF9C0-E1FB-4F68-9F2C-99649A67E218/L0/001","18D08CEC-4075-4488-BFD1-E9403B214356/L0/001","74257416-6D9C-48B2-9CE0-C23B56CB4171/L0/001","2EA7CACE-9B9B-4FC9-ABC5-03BCE2BDAA2A/L0/001","46A4CD2B-4FEB-4BBE-86DC-B79ED49BC300/L0/001","E4290EB0-2B16-46AE-9B98-83379F6128F3/L0/001","7C0B36FF-320D-4083-92E4-5A1F464FFFB1/L0/001","DEE1414C-2B92-4147-8C3C-A1775FB324AD/L0/001"]
    
class DetailViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout{
    
    var myCollectionView: UICollectionView!
    let imgManager = PHImageManager.default()
    let requestOptions = PHImageRequestOptions()
    var fetchResult: PHFetchResult<PHAsset>!
    
    override func viewDidLoad() {
       
        let requestOptions = PHImageRequestOptions()
        requestOptions.isSynchronous = false
        let layout = UICollectionViewFlowLayout()
        myCollectionView = UICollectionView(frame: self.view.frame,collectionViewLayout: layout)
        myCollectionView.delegate = self
        myCollectionView.dataSource = self
        myCollectionView.backgroundColor = UIColor.white
        myCollectionView.allowsMultipleSelection = true
        myCollectionView.register(ImageEditCell.self,forCellWithReuseIdentifier: "Cell")
        myCollectionView.showsVerticalScrollIndicator = false
        self.view.addSubview(myCollectionView)
let asset = PHAsset.fetchAssets(withLocalIdentifiers: [identifier],options: .none)

    }
    func collectionView(_ collectionView: UICollectionView,cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell",for: indexPath) as! ImageEditCell
        cell.representedAssetIdentifier = identifier[indexPath.row]
       
        imgManager.requestImage(for: asset!,targetSize: CGSize(width:120,height: 120),contentMode: .aspectFill,options: requestOptions,resultHandler: { result,info in
                                    if cell.representedAssetIdentifier == self.identifier {
                                        cell.imageview.image = result
                                    }
                                })
    }
}

,

我最终想通了。我意识到我没有正确地将标识符转换为UIImage，所以即使我已修复了OP中的错误，由于该解决方案还有很多其他问题，它仍然无法正常工作。下面是我要工作的解决方案：

    var myCollectionView: UICollectionView!
    var imageViews = [UIImageView]()
    var identifier = [
        "83BDF9C0-E1FB-4F68-9F2C-99649A67E218/L0/001","DEE1414C-2B92-4147-8C3C-A1775FB324AD/L0/001"
    ]
    
    override func viewDidLoad() {
        let layout = UICollectionViewFlowLayout()
        myCollectionView = UICollectionView(frame: self.view.frame,collectionViewLayout: layout)
        myCollectionView.delegate = self
        myCollectionView.dataSource = self
        myCollectionView.backgroundColor = UIColor.white
        myCollectionView.allowsMultipleSelection = true
        myCollectionView.showsVerticalScrollIndicator = false
        myCollectionView.register(CollectionCell.self,forCellWithReuseIdentifier: "Cell")
        self.view.addSubview(myCollectionView)
    }
    func collectionView(_ collectionView: UICollectionView,numberOfItemsInSection section: Int) -> Int {
        return identifier.count
    }
    func collectionView(_ collectionView: UICollectionView,for: indexPath) as! CollectionCell
        
        let options = PHFetchOptions()
        let results = PHAsset.fetchAssets(withLocalIdentifiers: identifier,options: options)
        let manager = PHImageManager.default()
        results.enumerateObjects { (thisAsset,_,_) in
            manager.requestImage(for: thisAsset,targetSize: CGSize(width: 200.0,height: 200.0),contentMode: .aspectFit,options: nil,resultHandler: {(thisImage,_) in
                self.imageViews.append(UIImageView(image: thisImage))
            })
        }
        let image = imageViews[indexPath.item]
        cell.imageView.image = image.image
        return cell
    }