swift中从UICollectionViewDataSource继承时的泛型类

Question

当我尝试创建一个在 swift 中实现 UICollectionViewDataSource 的通用类时，它说我的类不符合协议（有时 Xcode 崩溃）。

这是否意味着我们不能为 UICollectionView 创建通用数据提供者并且我们必须复制代码？

这是通用代码：

// Enum protocol
protocol OptionsEnumProtocol
{
    typealias T
    static var allValues:[T] {get set}
    var description: String {get}
    func iconName() -> String
}

// enum : list of first available options
enum Options: String, OptionsEnumProtocol
{
    typealias T = Options

    case Color = "Color"
    case Image = "Image"
    case Shadow = "Shadow"

    static var allValues:[Options] = [Color, Image, Shadow]

    var description: String {
        return self.rawValue
    }

    func iconName() -> String
    {
        var returnValue = ""

        switch(self)
        {
            case .Color: returnValue = "color_icon"
            case .Image: returnValue = "image_icon"
            case .Shadow: returnValue = "shadow_icon"
        }

        return returnValue
    }
}

// class to use as the uicollectionview datasource and delegate
class OptionsDataProvider<T>: NSObject, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout
{
    private let items = T.allValues

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
    {
        return items.count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
    {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(OptionsCellReuseIdentifier, forIndexPath: indexPath) as! GenericIconLabelCell

        let item = self.items[indexPath.row]
        // Configure the cell
        cell.iconFileName = item.iconName()
        cell.labelView.text = item.description

        return cell
    }
}

但因为失败了，我不得不改用这种非通用形式：

enum Options: String
{
    case Color = "Color"
    case Image = "Image"
    case Shadow = "Shadow"

    static var allValues:[Options] = [Color, Image, Shadow]

    var description: String {
        return self.rawValue
    }

    func iconName() -> String
    {
        var returnValue = ""

        switch(self)
        {
            case .Color: returnValue = "color_icon"
            case .Image: returnValue = "image_icon"
            case .Shadow: returnValue = "shadow_icon"
        }

        return returnValue
    }
}

class OptionsDataProvider: NSObject, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout
{
    private let items = Options.allValues

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
    {
        return items.count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
    {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(OptionsCellReuseIdentifier, forIndexPath: indexPath) as! GenericIconLabelCell

        let item = self.items[indexPath.row]
        // Configure the cell
        cell.iconFileName = item.iconName()
        cell.labelView.text = item.description

        return cell
    }
}

这使我有义务为我拥有的每种枚举类型复制该类。

确切的错误：

Answer 1

你是对的，写一个泛型类是不可能的。但是，我找到了一种解决方法。它不使用枚举，所以也许你觉得它不是很有用。然而，它实现了你想要的——你得到了一个集合视图数据源，它可以与不同的类一起使用，提供必要的数据。代码如下：

protocol OptionsProviderProtocol
{
    func allValues() -> [OptionsItem]
}

class OptionsItem:NSObject {
    let itemDescription:String
    let iconName:String

    init(iconName:String,description:String) {
        self.itemDescription = description
        self.iconName = iconName
    }
}

// class stores first available options
class Options: NSObject, OptionsProviderProtocol
{

    let color = OptionsItem(iconName: "color_icon", description: "Color")
    let image = OptionsItem(iconName: "image_icon", description: "Image")
    let shadow = OptionsItem(iconName: "shadow_icon", description: "Shadow")

    func allValues() -> [OptionsItem] {
        return [color, image, shadow]
    }
}

// class to use as the uicollectionview datasource and delegate
class OptionsDataProvider: NSObject, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout
{
    private var items:[OptionsItem] = []

    convenience init(optionsProvider:OptionsProviderProtocol) {
        self.items = optionsProvider.allValues()
    }

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
    {
        return items.count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
    {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(OptionsCellReuseIdentifier, forIndexPath: indexPath) as! GenericIconLabelCell

        let item = self.items[indexPath.row]
        // Configure the cell
        cell.iconFileName = item.iconName()
        cell.labelView.text = item.description

        return cell
    }
}

如果您有任何问题，请告诉我。

Answer 2

当您从协议继承时，您必须实现所有必需的方法。 Swift 2 将对此有所改变。也许你真的想从一个类继承。

Answer 3

当我尝试从 NSOperation 类继承 Generic 类时，我遇到了类似的 problem/question。 xCode 没有给我编译错误，因为没有涉及任何协议，而是我的 override func main() 根本没有被调用:)

无论如何...如果您关注workaround 那位先生。 Topal Sergey 建议，您可以相对轻松地实现您想要的。

class ViewController: UIViewController {

    @IBOutlet weak var collectionView: UICollectionView?
    private var defaultDataProvider = OptionsDataProvider<Options>()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        collectionView?.delegate = defaultDataProvider
        collectionView?.dataSource = defaultDataProvider
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}


// Enum protocol
protocol OptionsEnumProtocol {
    static var allValues: [OptionsEnumProtocol] {get set}
    var description: String {get}
    func iconName() -> String
}

// enum : list of first available options
enum Options: String, OptionsEnumProtocol {
    case Color = "Color"
    case Image = "Image"
    case Shadow = "Shadow"

    static var allValues: [OptionsEnumProtocol] = [Color, Image, Shadow]

    var description: String {
        return self.rawValue
    }

    func iconName() -> String
    {
        var returnValue = ""

        switch(self)
        {
        case .Color: returnValue = "color_icon"
        case .Image: returnValue = "image_icon"
        case .Shadow: returnValue = "shadow_icon"
        }

        return returnValue
    }
}

class OptionsDataProviderWrapper: NSObject, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    // MARK: protocols' funcs

    final func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return wrapperCollectionView(collectionView, numberOfItemsInSection: section)
    }

    final func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        return wrapperCollectionView(collectionView, cellForItemAtIndexPath: indexPath)
    }

    // MARK: for override

    func wrapperCollectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 0
    }

    func wrapperCollectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        return UICollectionViewCell()
    }
}

class OptionsDataProvider<T: OptionsEnumProtocol>: OptionsDataProviderWrapper {
    private let items = T.allValues

    override func wrapperCollectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return items.count
    }

    override func wrapperCollectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("reuseId", forIndexPath: indexPath) as! GenericIconLabelCell

        let item = self.items[indexPath.row]
        cell.labelView?.text = item.description

        return cell
    }
}

class GenericIconLabelCell: UICollectionViewCell {
    @IBOutlet weak var labelView: UILabel?
}

这里的关键是创建OptionsDataProviderWrapper，它不是通用的并且实现了你的所有协议。它做的唯一一件事 - 它将调用重定向到另一个函数，如 func wrapperCollectionView...

现在您可以从此OptionsDataProviderWrapper 继承您的通用类并覆盖该包装函数。

注意：您必须完全覆盖包装函数，因为与我的 NSOperation 问题类似，不会在您的通用子类中调用原生 func collectionView... 函数。这就是为什么我用final 标记原生函数。