How to use the delegate Swift from the Objective-C?

I have a viewcontroller in Swift that works well, and I would like to use it from an Objective-C class. My problem is that I don't know how to use it.

I try to add the delegate in the header of my main Objective-C class.

@interface MainViewController : UIViewController <PlanningSearchDelegate>

But I think as it is a swift class, it doesn't work. The error is:
Cannot find protocol declaration for PlanningSearchDelegate

Then, I tried to add the @objc word in the swift class.

import UIKit

@objc protocol PlanningSearchDelegate
{
    func planningSearchDidSelectResult(_ result:DALSearchResult)
}

class PlanningSearchViewController: UIViewController 
{
}

extension PlanningSearchViewController: UITableViewDelegate
{
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)
    {
        let result = _results[indexPath.row]
        delegate?.planningSearchDidSelectResult(result)
    }
}

But I have an error message:

Method cannot be a member of an @objc protocol because the type of the parameter cannot be represented in Objective-C.

I put the delegate = self in the prepareForSegue of the main Objective-C class without success :

else if ([segue.identifier isEqualToString:@"showSearchViewSegue"])
{
    PlanningSearchViewController *searchViewController = segue.destinationViewController;
    searchViewController.delegate = self;
}

The error message is:
Property 'delegate' not found on object of type "PlanningSearchViewController *'

Here is the DALSearchResult Class :

import Foundation

class DALSearchResult
{
    var contactId: Int
    var firstname: String
    var lastname: String
    var email: String
    var phone: String
    var city: String
    var registrationId: Int?
    var slotId: Int?
    var vehicleId: Int?
    var startDate: Date?
    var vehicleName: String?

    init(contactId:Int, firstname:String, lastname:String, email:String, phone:String, city:String)
    {
        self.contactId = contactId
        self.firstname = firstname
        self.lastname = lastname
        self.email = email
        self.phone = phone
        self.city = city
    }

    convenience init(registrationId:Int, slotId:Int, vehicleId:Int, contactId:Int, firstname:String, lastname:String, email:String, phone:String, city:String, startDate:Date, vehicleName: String)
    {
        self.init(contactId: contactId, firstname: firstname, lastname: lastname, email: email, phone: phone, city: city)

        self.registrationId = registrationId
        self.vehicleId = vehicleId
        self.slotId = slotId
        self.startDate = startDate
        self.vehicleName = vehicleName
    }
}

Anyone has an idea ?

Thanks in advance.