A simple UISearchController with an activity indicator at search icon.

UISearchControllerWithIndicator.swift

//
//  UISearchControllerWithIndicator.swift
//
//  Created by Afshin Hoseini on 2/10/16.
//  https://github.com/afshin-hoseini
//

import Foundation
import UIKit

class UISearchControllerWithIndicator: UISearchController {
    
    private var didPutActivityIndicator = false
    private var searchTextField: UIView? = nil
    private var activityIndicator: UIActivityIndicatorView? = nil
    private var searchIcon: UIImageView? = nil
    
    
    private func putActivityIndicator() {
        
        guard !didPutActivityIndicator else { return }
        
        let containerView = self.searchBar.subviews[0]
        
        activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: UIActivityIndicatorViewStyle.Gray)
        activityIndicator!.frame = CGRectMake(0, 0, 0, 0)
        
        //Inserts activity indicator inside the UISearchTextField
        
        for var i=0; i < containerView.subviews.count; i++ {
            
            let view = containerView.subviews[i]
            
            if view is UITextField {
                
                for v in view.subviews {
                    
                    if v is UIImageView {
                        
                        searchIcon = v as? UIImageView
                    }
                    
                    searchTextField = view
                    view.addSubview(activityIndicator!)
                    didPutActivityIndicator = true
                }
                
                break
            }
        }
    }
    

    
    var showActivityIndicator: Bool = false {
        
        didSet {
            
            putActivityIndicator()
            
            if showActivityIndicator {
                
                activityIndicator?.startAnimating()
                
                self.activityIndicator!.frame = CGRectMake(self.searchIcon!.frame.origin.x, self.searchIcon!.frame.origin.y, self.searchIcon!.frame.size.width, self.searchIcon!.frame.size.height)
                self.activityIndicator?.alpha = 0
                self.searchIcon?.alpha = 1
                
                UIView.animateWithDuration(0.5, animations: { () -> Void in
                    
                    self.activityIndicator?.alpha = 1
                    self.searchIcon?.alpha = 0
                })
                
            }
            else {
                
                UIView.animateWithDuration(0.5, animations: { () -> Void in
                    
                    self.activityIndicator?.alpha = 0
                    self.searchIcon?.alpha = 1
                })
            }
            
        }
    }
    
}

Basically this class derived UISearchController and shows an UIActivityIndicator instead the magnifier icon by setting the showActivityIndicator to true and vice versa, with alpha animation