swift：在NavigationItem中，当我使用navigationBar中的后退按钮返回时，CartValue消失了

Question

我在很多ViewController的导航栏上都有一个购物车。随着增加和减少，正确显示在购物车上的值。问题是当我单击导航栏中的后退按钮时，之前的viewController购物车价值消失了。

import UIKit
import Foundation


var navCartLabel = UILabel()

HomeController的

class HomeCollectionViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout{



    func navCartDataLoad(POST_PARAMETERS: Dictionary<String, String>){

        NetworkRequestAPI.postAndGet(params: POST_PARAMETERS, url: Configuration.URL_TO_ADD_CART_FOR_MAINACTIVITY) { (response, error) in

            DispatchQueue.main.async(execute: {

                let json: [String:Any] = response


                if(!error)  {

                    do {


                    } catch let error as NSError {
                        print(error)
                    }

                    DispatchQueue.main.async(execute: {

                        if let myCartText = json["cart_item_count"] as? Int {

                            navCartLabel.text = "\(myCartText)"

                            print("cart text api \(myCartText)")


                        }
                    })

                }


            })

        }
    }

viewDidLoad中

    override func viewDidLoad() {
        super.viewDidLoad()


     setupHomeNavBarBtn()


    }

viewWillAppear中

   override func viewWillAppear(_ animated: Bool) {

        super.viewWillAppear(animated)

       let user_id = UserDefaults.standard.string(forKey: "user_id")

        if user_id != nil {

            print(" cart  not nill")

            navCartLabel.backgroundColor = .red
            navCartLabel.textColor = .white

            print("cart label value \(navCartLabel.text)")



            let POST_PARAMETERS = ["user_id": user_id]


            self.navCartDataLoad(POST_PARAMETERS: POST_PARAMETERS as! Dictionary<String, String>)



        } else {

            print("cart nil ")
            navCartLabel.backgroundColor = .clear
            navCartLabel.textColor = .clear
        }

    }


    **setupNavigation Item**
    func setupHomeNavBarBtn() {

        let navCartBtn = UIButton()
        navCartBtn.frame = CGRect(x: 0, y: 0, width: CollectionViewSize.width / 15, height: CollectionViewSize.width / 15)

        navCartBtn.contentEdgeInsets = UIEdgeInsetsMake(0, 0, CollectionViewSize.width / 60, 0)

        navCartBtn.setImage(UIImage(named: "cart_empty"), for: .normal)
        navCartBtn.contentMode = .scaleAspectFit
       // navCartBtn.addTarget(self, action: #selector(navCartBtnClick), for: .touchUpInside)


        navCartLabel.font = UIFont.systemFont(ofSize: CollectionViewSize.width / 40)
        navCartLabel.backgroundColor = .red

        navCartLabel.frame = CGRect(x: CollectionViewSize.width / 37.5, y: -(CollectionViewSize.width / 75), width: CollectionViewSize.width / 25, height: CollectionViewSize.width / 25)
        navCartLabel.layer.cornerRadius = CollectionViewSize.width / 50
        navCartLabel.layer.masksToBounds = true
        navCartBtn.addSubview(navCartLabel)


        let cartBarBtnItem = UIBarButtonItem(customView: navCartBtn)

       self.navigationItem.setRightBarButtonItems([cartBarBtnItem], animated: true)
  }

}

Answer 1

尝试在setupHomeNavBarBtn内移动viewWillAppear，例如：

override func viewWillAppear(_ animated: Bool) {
   super.viewWillAppear(animated)

  //... your other stuff here...

   self.setupHomeNavBarBtn()
}