将消息从View Controller传递到Swift中的类

Question

By using delegates, I'm trying to pass data from a view controller to a TableView class that will display the correct number of cells. First, I needed to pass the array to that class (using a String here instead for debugging)

Inside my ViewController:

protocol GroupBillVCDelegate{
  func passFriendArray(string: String)
}

...
class GroupBillViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{
    var delegate:GroupBillVCDelegate? // for delegate passing message

    ...

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        if (tableView == self.FriendTableView){
            let friendListCell = tableView.dequeueReusableCell(withIdentifier: "friendListCell") as! CategoryRow

            // transfer friends array to CategoryRow
            self.delegate?.passFriendArray(string: "Hello There")

            return friendListCell
        }
    }
}

Inside the TableViewCell class:

class CategoryRow: UITableViewCell, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, GroupBillVCDelegate {

    var s:String = String()

    func passFriendArray(string: String) {
        s = string
        print(string)
    }

...

    // used for horizontal scrolling
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        passFriendArray(string: s)   // message supposed to appear here
        print ("TEST")
        return 10
    }

...

}

I have trouble setting up the delegate. When I run, the console does not display the message. Why is it not being passed?

Answer 1

Think of a delegate as an intercom on your desk that can be connected to your assistant's office.

This line:

var delegate:GroupBillVCDelegate? // for delegate passing message

Defines the intercom, but doesn't connect it to anything. If you press the button on the intercom, it doesn't connect to anything.

The code self.delegate?.passFriendArray(string: "Hello There")

uses "optional chaining" to send a message to the delegate if there is one, and drop the message if there is no delegate.

The thing you're missing is assigning something to the delegate:

self.delegate = someObjectThatConformsToGroupBillVCDelegateProtocol

A delegate is a one-to-one relationship.

All that being said, it doesn't really make sense to make a table view cell the delegate of a view controller. The table view has more than one cell. Which cell should be the view controller's delegate? Why that cell and not another one?