ios - 在 Swift 中导航时 TextField 卸载值

Question

我有两个 ViewController，每个都有一个用于获取用户输入数字的 TextField 和两个用于计算和导航的按钮。

SecondVC 中的 TextField 实例是用户在填充 TextFields 时创建的，它存在并显示在 View 中

问题是:当您在创建对象 - Cell 之后离开 SecondView Controller 并稍后返回时，它会被设置回 cero，这不是实例 - Cell 值

class MainViewController: UIViewController {

    @IBOutlet weak var A3TextField: UITextField!

    @IBAction func calc(_ sender: Any) {
        let A3 = Cell(name: "A3", sheet: "", value: Double(A3TextField.text!)!)
        print(A3)

    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

    }
}

class SecondViewController: UIViewController {

    @IBOutlet weak var B3TextField: UITextField!

    @IBAction func calc2(_ sender: Any) {
        let B3 = Cell(name: "B3", sheet: "", value: Double(B3TextField.text!)!)
        print(B3)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

    }

}

struct Cell {

    var name: String = ""
    var sheet: String = ""
    var value: Double = 0

    init(name: String, sheet: String, value: Double) {
        self.name = name
        self.sheet = sheet
        self.value = value
    }

}

Answer 1

当 Controller 弹出或推送时，它们的临时属性值或对象不能保存到其他 Controller ，即使在本身 Controller 中，当推送和返回时，它们是初始值，如果你想在页面切换时保存值，建议这些解决办法:

<强>1。传递抛出属性值(一=>二)

OneViewController:

let storyboard = UIStoryboard(name: "Main", bundle: nil)
 let twoVC = storyboard.instantiateViewController(withIdentifier: "TwoViewControllerID") as! twoViewController
 twoVC.myStr="Controller one to controller two!" 
 self.present(twoVC, animated: true, completion: nil)

TwoViewController

 var myStr=String()
  override func viewDidLoad() {
     super.viewDidLoad()
     print("get value：\(myStr)"

}

2、使用NSUerDfault保存并获取

设置值:

let userDefault = UserDefaults.standard
userDefault.set(name, forKey: "name")
userDefault.synchronize()

获取值:

let userDefault = UserDefaults.standard
let name = userDefault.object(forKey: "name") as? String

3,storybord传递值(一=>二)

override func prepare(for segue: UIStoryboardSegue, sender: Any?) { 
let theSegue=segue.destination as! twoViewController theSegue.myStr="other pass way" }

4,委托(delegate)传递值(二=>一)基于唐回到首页

TwoViewController:

//(1)create a delegate before class 
protocol FTVCdelegte : NSObjectProtocol{ 
//define method
// one method
 func change(title:String) 
 //two method
 func ChangeColoer (Coloer:UIColor)
 //three method
 func ChangSucces(YON:Bool) 
 } 

 //(2)create delegate object。 
var delegate_zsj:FTVCdelegte? 

//(3)click back button
 @IBAction func backBtnAction(_ sender: UIButton) { 
 delegate_zsj?.change(title: "main page") 
 delegate_zsj?.ChangeColoer(Coloer: UIColor.red) 
 delegate_zsj?.ChangSucces(YON: true) 
 self.navigationController?.popViewController(animated: true)
 }

OneViewController

//(4)inherit delegate： 
class SecondViewController: UIViewController,FTVCdelegte,ChangeBtnDelege{
...
//(5)imple delegate method 

 func change(title: String) { self.title = title } 

 func ChangeColoer(Coloer: UIColor) { self.view.backgroundColor = Coloer } 

 func ChangSucces(YON: Bool) { print(YON) } 

 //(6)when pop page use
 @IBAction func tiaozhuanBtnAction(_ sender: Any) { 
 let storyboard = UIStoryboard(name: "Main", bundle: nil)
 let oneVC = storyboard.instantiateViewController(withIdentifier:   "OneViewControllerID") as! oneViewController 
 oneVC.delegate_zsj = self 
 self.navigationController?.pushViewController(oneVC, animated: true) 
 }

5,区 block 传递值(二=>一)基于唐回到首页

TwoViewController:

//(1)define a block method：
var bbchange:((_ title:String,_ myColor:UIColor)->Void)? 

//(2)back to front page：
@IBAction func backBtnAction(_ sender: UIButton) { 
bbchange?("document",UIColor.green) 
self.navigationController?.popViewController(animated: true)

}

OneViewController

//(3)next page invoke block  method
@IBAction func tiaozhuanBtnAction(_ sender: Any) { 
let storyboard = UIStoryboard(name: "Main", bundle: nil) 
let threeVC = storyboard.instantiateViewController(withIdentifier:    "twoViewControllerID") as! twoViewController 
twoVC.bbchange=
{ 
  ( title:String,myColor:UIColor) in 
  self.title=title 
  self.view.backgroundColor=myColor
} 
self.navigationController?.pushViewController(twoVC, animated: true)
}