Swift: My custom UITableViewDataSource class thinks it doesn't conform to protocol 'UITableViewDataSource'

Question

I have checked a few other questions out there, of which the answers seem to be in the datasource methods' declarations. However, I cannot find what's wrong with my methods declarations.

Here is my class:

import UIKit

class GuestControl: UITableViewDataSource, UITableViewDelegate {
    @IBOutlet weak var leftTable: UITableView!
    @IBOutlet weak var rightTable: UITableView!
    var userList = [User]() //even numbers including 0 go on the left table, odd numbers go on the

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    //Here is where we link to that user's contact page
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell: GuestTableViewCell = tableView.dequeueReusableCellWithIdentifier("guestCell") as! GuestTableViewCell

    if tableView == leftTable {
        cell.configureCellWithUser(userList[indexPath.row+indexPath.row])
    } else {
        cell.configureCellWithUser(userList[indexPath.row+indexPath.row+1])
    }

    return cell
}

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    let num = Double(userList.count) / 2.0
    if tableView == leftTable {
        return Int(round(num)) //round up
    } else {
        return Int(num) //round down
    }
}

}

And here is the exact error:

Protocol requires function 'tableView(_:numberOfRowsInSection:)' with type '(UITableView, numberOfRowsInSection: Int) -> Int'
Candidate is not '@objc', but protocol requires it
Protocol requires function 'tableView(_:cellForRowAtIndexPath:)' with type '(UITableView, cellForRowAtIndexPath: NSIndexPath) -> UITableViewCell'
Candidate is not '@objc', but protocol requires it

What is wrong?

Answer 1

As the error message indicates, the protocol requires that the table view data source methods are "Objective-C compatible". This can be achieved by

• making your class inherit from NSObject (or any NSObject subclass)

  class GuestControl: NSObject, ...
  

• or adding the @objc attribute to the class definition

  @objc class GuestControl:  ...
  

• or adding the @objc attribute to the data source methods

  @objc func tableView(tableView: UITableView, numberOfRowsInSection section: Int) ...
  

In the first two cases, all methods of the class are made Objective-C compatible.

If a (table) view controller is used as the table view data source then this automatically satisfied because UI(Table)ViewController inherits from NSObject.