UISearchBar category and extension for conveniently customize the text fields within search bar. Via test confirm, compatible from iOS 9 to iOS 13

UISearchBar+Extension.swift

//
//  UISearchBar+Extension.swift
//

import UIKit

extension UISearchBar {
    
    var dtXcode: Int {
        if let dtXcodeString = Bundle.main.infoDictionary?["DTXcode"] as? String {
            if let dtXcodeInteger = Int(dtXcodeString) {
                return dtXcodeInteger
            }
        }
        return Int()
    }

    /**
        * Due to searchTextField property who available iOS 13 only, extend this property for iOS 13 previous version compatibility
     
     ### Usage Example: ###
     
     ````
     
     var searchController: UISearchController?
     
     // Change Search Bar Text Color
     searchController?.searchBar.compatibleSearchTextField.textColor = UIColor.XXX
     
     // Change Search Bar Background Color
     searchController?.searchBar.compatibleSearchTextField.backgroundColor = UIColor.XXX
     
     ````
     
     */
    var compatibleSearchTextField: UITextField {
        guard #available(iOS 13.0, *), dtXcode >= 1100 else { return legacySearchField }
        return self.searchTextField
    }
    
    var legacySearchField: UITextField {
        // iOS 13 previous, UISearchBar with both section of UISearchBarBackground and UITextField.
        guard let textField = self.subviews.first?.subviews.last as? UITextField else { return UITextField() }
        return textField
    }
}

UISearchBar+SearchTextField.h

//
//  UISearchBar+SearchTextField.h
//

@interface UISearchBar (SearchTextField)
    
/**
    * Due to searchTextField property who available iOS 13 only, extend this property for iOS 13 previous version compatibility
    
 ### Usage Example: ###
     
 ````
 // Change Search Bar Text Color
 _searchBar.compatibleSearchTextField.textColor = [UIColor XXX];
     
 // Change Search Bar Background Color
 _searchBar.compatibleSearchTextField.backgroundColor = [UIColor XXX];
 ````
*/

@property (nonatomic, readonly) UITextField *compatibleSearchTextField;

@end

UISearchBar+SearchTextField.m

//
//  UISearchBar+SearchTextField.m
//

#import "UISearchBar+SearchTextField.h"

@implementation UISearchBar (SearchTextField)

- (UITextField *)compatibleSearchTextField {
    if (@available(iOS 13.0, *)) {
#ifdef __IPHONE_13_0
        return self.searchTextField;
#else
        // This condition is for Xcode 10 build iOS 13:
        return (UITextField *)[self valueForKey:@"searchField"];
#endif
    }
    else {
        // iOS 13 previous, UISearchBar with both section of UISearchBarBackground and UITextField.
        return [[[self.subviews firstObject] subviews] lastObject];
    }
}

@end