问xcode导航栏按钮状态

EN

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, introductionDelegate {

var navBarEditButton: UIBarButtonItem?
var navBarDeleteButton: UIBarButtonItem?
var navBarCancelButton: UIBarButtonItem?

override func viewDidLoad() {
    super.viewDidLoad()
    self.navBarEditButton = UIBarButtonItem(title: "Edit", style: .plain, target: self, action: #selector(editObjectsAction))
    self.navBarDeleteButton = UIBarButtonItem(title: "Delete", style: .plain, target: self, action: #selector(deleteObjectsAction))
    self.navBarCancelButton = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(cancelAction))

    self.navigationItem.leftBarButtonItems = [navBarEditButton!]
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@objc private func editObjectsAction(_ sender: UIBarButtonItem) {
    self.navigationItem.leftBarButtonItems = [navBarCancelButton!, navBarDeleteButton!]
}

@objc private func cancelAction(_ sender: UIBarButtonItem) {
    self.navigationItem.leftBarButtonItems = [navBarEditButton!]
}

@objc private func deleteObjectsAction(_ sender: UIBarButtonItem) {

}