UITableViewCell custom button image not displaying correctly after UITableView scrolled

I have a UITableViewCells that contains a custom button that is an image. When the button is pressed, the image changes. However, when I scroll up and down the tableView, the cell that is being used no longer displays the correct image, or the "tapped" image is displayed elsewhere. I understand this issue is due to cells being deferred and reused. What I was trying to do was create a delegate in my cell class. The delegate calls a method on the tableViewController class. I am doing this with code

self.delegate?.pressedButtonInCell?(self)

      

        
        
        
      

    

However, this doesn't work.

======= custom cell class = ===

import UIKit
@objc protocol BoostCellDelegate{
optional func pressedButtonInCell(cell:BoostCell)
optional func displayAlert (title:String , error: String)
}
class BoostCell: UITableViewCell {
var delegate:BoostCellDelegate?
var boosted = false
var boostedButton = UIImage(named: "boostButtons.png")
@IBOutlet var userImage: UIImageView!
@IBOutlet var name: UILabel!

@IBOutlet var createdAt: UILabel!
@IBOutlet var boostButton: UIButton!
@IBAction func boostPressed(sender: UIButton) {

        let objectId = sender.titleLabel!.text!
        var query = PFQuery(className:"boostPost")
        query.getObjectInBackgroundWithId(objectId) {
            (boostPost: PFObject!, error: NSError!) -> Void in
            if error != nil {
                NSLog("%@", error)
                self.delegate?.displayAlert?("Something gone wrong", error: "Might be the bad reception")
            } else {
                if boostPost != nil{
                    if boostPost["boostedBy"] != nil {
                        var boostedByArray : NSArray = boostPost["boostedBy"] as NSArray
                        if boostedByArray.containsObject(PFUser.currentUser().username){
                            println("username already boosted")

                        }
                        else{
                        var boostNumber = boostPost["boostNumber"] as Int
                        boostNumber++
                        boostPost["boostNumber"] = boostNumber
                        boostPost.addObject(PFUser.currentUser().username, forKey:"boostedBy")
                        boostPost.saveInBackground()
                        println("new username added to boosted")
                        self.delegate?.pressedButtonInCell?(self)
                        }
                    }
                    else if boostPost["boostedBy"] == nil{
                    var boostNumber = boostPost["boostNumber"] as Int
                    boostNumber++
                    boostPost["boostNumber"] = boostNumber
                    boostPost.addObject(PFUser.currentUser().username, forKey:"boostedBy")
                    boostPost.saveInBackground()
                    println("new username added to boosted")
                    self.delegate?.pressedButtonInCell?(self)

      

        
        
        
      

    

==================================== code in class tableViewController ====== ===

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as BoostCell

    cell.name.text = userNewNames[indexPath.row]
    cell.content.text = userNewContent[indexPath.row]
    var dateFormatter = NSDateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd"
    cell.createdAt.text = userCreatedAt[indexPath.row]
    cell.delegate = self

    if userBoostedBy[indexPath.row].count == 2 {
        cell.boostedBy.text = "1 boost"
    }
    else if userBoostedBy[indexPath.row].count > 2 {
        var count = userBoostedBy[indexPath.row].count - 1
        cell.boostedBy.text = "\(count) boosts"
    }
    else {
        cell.boostedBy.text = "0 boost"
    }

    if (userButtonState[indexPath.row] == true) {
        cell.boostButton.setImage(self.boostedButton, forState: UIControlState.Normal)
    }
    else {
        cell.boostButton.setImage(self.unBoostedButton, forState: UIControlState.Normal)
    }

    userImagesFiles[indexPath.row].getDataInBackgroundWithBlock({ (imageData:NSData!, error:NSError!) in
        if error == nil {
            let image = UIImage(data: imageData)
            cell.userImage.image = image
        }
    })
    cell.boostButton.setTitle(objectIds[indexPath.row], forState: UIControlState.Normal)
    func pressedButtonInCell(cell:BoostCell)
    {
        cell.boostButton.setImage(self.boostedButton, forState: UIControlState.Normal)
    }
    // function to display the alert message
    func displayAlert (title:String , error: String){
        var alert = UIAlertController(title: title, message: error, preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: {
            action in

        }))
        self.presentViewController(alert, animated: true, completion: nil)
    }
    return cell
}