Generic class when inherit from UICollectionViewDataSource in swift

Question

when I try to create a generic class which implement UICollectionViewDataSource in swift it say that my class does not conform to protocol (and sometime Xcode crash).

Does it mean that we can't create generic data provider for UICollectionView and that we have to duplicate code ?

Here is the generic code :

// 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
    }
}

But because it failed I have to use this non generic form instead :

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
    }
}

which obligate me to duplicate the class for each enum type I have.

Exact error :

Answer 1

You are right, it is not possible to write a generic class. However, I have found a workaround. It doesn't use enums and so maybe you don't find it very useful. However, it achieves what you want - you are getting a collection view data source which can be used with different classes providing necessary data. Here is the code:

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
    }
}

If you have any questions please let me know.