Add a custom button between UISearchBar and Cancel button while a search is enabled

UISearchBarWithCustomButtonExample.swift

private lazy var customSearchButton = UIButton(
    type: .contactAdd, 
    primaryAction: UIAction(handler: { _ in })
)

private func configureSearchController() {
    let searchController = UISearchController(searchResultsController: /*YOUR_SEARCH_CONTROLLER*/)
    searchController.delegate = self
                                              
    // Set custom leading padding to the cancel button (size of our button + some padding)
    searchController.searchBar.perform(Selector(("_setAdditionalPaddingForCancelButtonAtLeadingEdge:")), with: Double(40))
    
    // Add our custom button to the _UISearchBarSearchContainerView and attach to the searchTextField
    let searchTextField = searchController.searchBar.searchTextField                                         
    if let searchTextFieldContainerView = searchTextField.superview {
        searchTextFieldContainerView.addSubview(self.customSearchButton)
        self.customSearchButton.alpha = 0
        self.customSearchButton.snp.makeConstraints { make in
            make.size.equalTo(36)
            make.left.equalTo(searchTextField.snp.right).offset(8)
            make.centerY.equalTo(searchTextField)
        }
    }
}

func willPresentSearchController(_ searchController: UISearchController) {
    UIView.animate(withDuration: 0.25) { self.customSearchButton.alpha = 1 }
}

func willDismissSearchController(_ searchController: UISearchController) {
    UIView.animate(withDuration: 0.25) { self.customSearchButton.alpha = 0 }
}