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Roger Molas
Roger Molas

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Access class name using @objc attribute

Scenario

  • Create a Simple Table View app
  • Load customs cells each row
  • Cell identifier is the class name if the object is TableCell cell identifier is "TableCell"
  • Use common cell loading techniques
  • Use helper method to load cell using @objc attribute

Create UITableViewCell subclass

class HeaderCell: UITableViewCell {
    ...
}
class ContentsCell: UITableViewCell {
    ...
}
class AboutCell: UITableViewCell {
    ...
}

Load cell in Tableview in traditional way

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if indexPath.row == 0 {
        let cell = tableView.dequeueReusableCell(withIdentifier: "HeaderCell", for: indexPath) as? HeaderCell
        return cell
    }
    if indexPath.row == 2 {
        let cell = tableView.dequeueReusableCell(withIdentifier: "ContentsCell", for: indexPath) as? ContentsCell
        return cell
    }
    if indexPath.row == 1 {
        let cell = tableView.dequeueReusableCell(withIdentifier: "AboutCell", for: indexPath) as? AboutCell
        return cell
    }
    return UITableViewCell()
}

So whats @objc attribute?
When you apply it to a class or method it instructs Swift to make those things available to Objective-C as well as Swift code.

Most of the time you see @objc when you call a method from a UIBarButtonItem or UIButton, you’ll need to mark that method using @objc so it’s exposed – both of those, and many others, are Objective-C code.

In this case, we will use @objc to name our subclasses HeaderCell, ContentsCell, and AboutCell in Swift

Update our UITableViewCell subclass

@objc(HeaderCell)
class HeaderCell: UITableViewCell {
    ...
}
@objc(ContentsCell)
class ContentsCell: UITableViewCell {
    ...
}
@objc(AboutCell)
class AboutCell: UITableViewCell {
    ...
}

Create a Helper method to take the cell identifier using the AnyClass type from the UITableViewCell subclass.

Note: Cell identifier should be the class name

func getCell(_ cls: AnyClass, _ index: IndexPath) -> AnyObject {
    let identifier = NSStringFromClass(cls)
    let cell = tableView.dequeueReusableCell(withIdentifier: identifier, for: index)
    return cell
}

Load cell in Tableview using new way

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if indexPath.row == 0 {
        let cell = getCell(HeaderCell.self, indexPath) as! HeaderCell
        return cell
    }
    if indexPath.row == 2 {
        let cell = getCell(ContentsCell.self, indexPath) as! ContentsCell
        return cell
    }
    if indexPath.row == 1 {
        let cell = getCell(AboutCell.self, indexPath) as! AboutCell
        return cell
    }
    return UITableViewCell()
}

Looks clean right?, so @objc attribute is not just for methods, we use it to name our class as well.

Addition Tricks

Let's make it shorter, create an enum of rows called Row

enum Row: Int {
    case HeaderCell = 0
    case ContentsCell = 1
    case AboutCell  = 2

    var className: AnyClass {
        switch self {
            case .Header:
                return HeaderCell.self
            case .Contents:
                return ContentsCell.self
            case .About:
                return AboutCell.self
        }
    }
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let row = Row(rawValue: indexPath.row)
    let cell = getCell(row.className, indexPath) // dynamic binding
    return cell
}

That's it!
Thanks for your time

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