Question

我有UICollectionView，其模型如下：

class MainVCModel {

    let models = [
        CellModel.init(UIImage.init(named: "1.jpg")!),
        CellModel.init(UIImage.init(named: "2.jpg")!),
        CellModel.init(UIImage.init(named: "3.jpg")!),
        CellModel.init(UIImage.init(named: "4.jpg")!),
        CellModel.init(UIImage.init(named: "5.jpg")!),
        CellModel.init(UIImage.init(named: "6.jpg")!),
        CellModel.init(UIImage.init(named: "7.jpg")!),
        CellModel.init(UIImage.init(named: "8.jpg")!),
        CellModel.init(UIImage.init(named: "9.jpg")!),
    ]
}

struct CellModel {
    var isEnlarged: Bool = false
    var image: UIImage

    lazy var rotatedImage: UIImage = self.image.rotate(radians: Float(Helper.degreesToRadians(degrees: 6)))!

    init(_ image: UIImage){
        self.image = image
    }
}

在我的CollectionViewController类中，我有：

override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        var currentModel = model.models[indexPath.row]
        if !currentModel.isEnlarged {
            print("should enlarge")
            currentModel.isEnlarged = true
            enlargeOnSelection(indexPath)
        }   else {
            print("should restore")
            currentModel.isEnlarged = false
            restoreOnSelection(indexPath)
        }
    }

但是当我设置currentModel.isEnlarged = true时没有任何效果，它实际上存储了false的值，调试时我会注意到这一点。为什么？

Answer 1

在这一行：

var currentModel = model.models[indexPath.row]

如果models是一个结构数组，则currentModel是一个副本，因此设置属性currentModel不会影响该数组中的任何内容。

Answer 2

在将新值保存到主模型的副本中时，必须对此进行更新。

override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        var currentModel = model.models[indexPath.row]
        if !currentModel.isEnlarged {
            print("should enlarge")
            model.models[indexPath.row].isEnlarged = true
            enlargeOnSelection(indexPath)
        }   else {
            print("should restore")
            model.models[indexPath.row].isEnlarged = false
            restoreOnSelection(indexPath)
        }
    }

Answer 3

更改值后，您需要更新数组。由于struct是按值传递而不是引用。

currentModel = model.models[indexPath.row]
currentModel.isEnlarged = true
model.models[indexPath.row] = currentModel

添加前请务必检查索引是否可用。

更改结构的值无效

3 个答案: