Create a generic protocol for UITableView data source.

In our last post, we learned how to create and use a Generic Protocol by using the associated type. In this post, we will create a generic protocol for UITableView data source. You can use it for any UIViewController which has UITableView and follows the MVVM design pattern.

protocol TableListProtocol: AnyObject {
    associatedtype Item
    
    var numberOfSections: Int { get }
    
    func numberOfItems(in section: Int) -> Int
    func itemFor(index: Int,
                 section: Int) -> Item?
    func heightFor(index: Int,
                   section: Int) -> CGFloat
    func heightForHeder(in section: Int) -> CGFloat
    func heightForFooter(in section: Int) -> CGFloat
}

//Optional
extension TableListProtocol {
    func heightForHeder(in section: Int) -> CGFloat {
        return 0
    }
    
    func heightForFooter(in section: Int) -> CGFloat {
        return 0
    }
}

How to use it?
Suppose you have a Home Screen and in it you want to present a list view.
We are using an MVVM design pattern so we will have a HomeViewModel class. In HomeViewModel, we will write all the business logic for the Home Screen.

Here is the example using TableListProtocol

protocol HomeProtocol: AnyObject, TableListProtocol {
    var layout: HomeLayout { get }
}

final class HomeViewModel: HomeProtocol {
    typealias T = HomeModel
    private var items = [[HomeModel]]()
    
    init() {
        var items = [HomeModel]()
        for (_, item) in HomeItem.allCases.enumerated() {
            items.append(item.homeModel)
        }
        
        self.items.append(items)
    }
    
    var layout: HomeLayout {
        return .rightAligned
    }
    
    var numberOfSections: Int {
        return 1
    }
    
    func numberOfItems(in section: Int) -> Int {
        guard section >= 0, section < self.items.count else {
           return 0
        }
        
        return self.items[section].count
    }
    
    func itemFor(index: Int, 
                 section: Int) -> HomeModel? {
        guard index >= 0, index < numberOfItems(in: section) else {
            return nil
        }
        
        return items[section][index]
    }
    
    func heightFor(index: Int, 
                   section: Int) -> CGFloat {
        return 50.0
    }
}

//for better understanding 
struct HomeModel {
    let name: String
    let image: String?
}

In this example, you can see that there is a HomeProtocol that conforms the TableListProtocol. And HomeViewmodel conforms the HomeProtocol.
So HomeViewmodel will have to implement the methods and properties that are defined in the TableListProtocol + HomeProtocol.

So in the example, you can see that heightFor, itemFor, numberOfItems, and numberOfSections methods and behaviors implemented which defined the TableListProtocol.

Previous Post — https://medium.com/@abhinay.mca09/associated-types-generic-protocol-in-swift-edc7b27258e8

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