How to pass in parameters into @objc function

问题:

I have a cell in a tableView, with a button I want to add an action to.

The button will be an email address. When the button is pressed, I want to trigger a delegate that will have another ViewController open up an email. However, I need to be able to pass in the email as a parameter and Swift doesn't seem to let me do that.

Relevant code is below:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let row = self.sections[indexPath.section].rows[indexPath.row]
       switch row {
       case .Email:
            cell.infoLabel.setTitle(cellInfo.email, for: .normal)
            cell.infoLabel.addTarget(self, action: #selector(emailPressed(recipient: cellInfo.email!)), for: .touchUpInside)
            cell.imageType.image = UIImage(named: "Email")
       }
}

@objc func emailPressed(recipient: String){
        self.delegate?.dataController(self, recipientEmail: recipient)
    }

protocol DataControllerDelegate: class {
    funcdataController(_ DataController: DataController, recipientEmail: String)
}

I'm getting the error: "Argument of '#selector' does not refer to an '@objc' method, property, or initializer"

Is there a way to pass in the email to the @objc function so that it can feed into the delegate function?

回答1:

You can subclass UIButton and add a recipientEmail variable to it.

class RecipientButton: UIButton {

    var recipientEmail: String?

    override init(frame: CGRect) {
        super.init(frame: frame)

    }

    required init(coder aDecoder: NSCoder) {
        fatalError("This class does not support NSCoding")
    }
}

Inside your cell, instead of having infoLabel as of type UIButton have it as of type RecipientButton

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let row = self.sections[indexPath.section].rows[indexPath.row]
    switch row {
        case .Email:
            cell.infoLabel.setTitle(cellInfo.email, for: .normal)
            cell.infoLabel.recipentEmail = cellInfo.email
            cell.infoLabel.addTarget(self, action: #selector(emailPressed(_ :)), for: .touchUpInside)
            cell.imageType.image = UIImage(named: "Email")
    }
}

@objc func emailPressed(_ sender: RecipientButton) {
    guard let email = sender.recipientEmail else { return }
    self.delegate?.dataController(self, recipientEmail: email)
}

回答2:

You cannot pass anything into a target's action method. You don't call the method; the target-action architecture calls it when the button is tapped. The action method must take one parameter, namely the sender (which in this case will be the button).

If the action method needs more information at the time that it is called, you must provide that information in some other way, e.g. as an instance property that the action method can access when it is called.