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Xcode – How do I correctly use fetch assets with a local identifier?

I am trying to figure out how to get an array of identifiers and put them in a collection view programmatically. Correct me if I am wrong but, I believe the best way to do this is by using PHAsset.fetchAssets. At most I anticipate the users fetching 10 images (avg. 3-4) so I do not think the process would be very resource intensive. I am testing the code below with a specific array of identifiers. In the cellForItemAt function on the line where I assign the asset I get an error message. See the comment above that line. I have seen similar issues on SO but I have not been able to apply anything that I found. What am I doing wrong?

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
                                    }
                                })
    }
}
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2

Answers


  1. Chosen as BEST ANSWER
    0

    I eventually figured it out. I realized i was not correctly converting the identifier to a UIImage so even if I had fixed the error in the OP it still would not work because of numerous others that would have come up with that solution. Below is the solution i got to work:

        var myCollectionView: UICollectionView!
    var imageViews = [UIImageView]()
    var identifier = [
        "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"
    ]
    
    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, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", 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
    }

  2. 0

    Here I’ve moved fetch function to viewDidLoad in order to prevent other errors and also I am not sure what you are fetching whether it is an array with images(if so then by putting .firstObject you are fetching a single image which may cause an error)

    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
                                    }
                                })
    }
}
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