当按下按钮上的标签值时，发现致命的“错误：意外地发现零，同时展开可选值”按

Question

当我按下按钮时，我总是得到零值。

import UIKit 

class ViewController: UIViewController { 
//MARK: Properties 

@IBOutlet weak var txt_vrednost: UITextField! 
@IBOutlet weak var btn_dodaj: UIButton! 
@IBOutlet weak var lbl_stanje: UILabel! 
var novcanik = 0.0 

//MARK: Acttion 

@IBAction func btn_dodaj_pressed(_ sender: Any) { 

    let values = Double(txt_vrednost.text!) 
    novcanik = novcanik + values! 
    lbl_stanje.text=String(novcanik) 

} 

override func viewDidLoad() { 
    super.viewDidLoad() 

    // Do any additional setup after loading the view, typically from a nib. 
    } 
} 

Answer 1

首先确保您的所有插座都与故事板连接。你正在使用武力解开到处，这是导致崩溃：

import UIKit 

class ViewController: UIViewController { 

//MARK: Properties 

@IBOutlet weak var txt_vrednost: UITextField! 
@IBOutlet weak var btn_dodaj: UIButton! 
@IBOutlet weak var lbl_stanje: UILabel! 

var novcanik = 0.0 

//MARK: Action 

@IBAction func btn_dodaj_pressed(_ sender: Any) { 
    guard let values = txt_vrednost.text as? Double else { 
     print("not convertible") 
     return 
    } 
novcanik = novcanik + values 
lbl_stanje.text = "\(novcanik)" 
} 

override func viewDidLoad() { 
super.viewDidLoad() 

// Do any additional setup after loading the view, typically from a nib. 

} 
}