ios - 如何在展开之前分配这些对象？

Question

所以，当我从 Android 开发转向 IOS 时，我试图制作自己的计算器来娱乐，现在我尝试纠正这个错误 40 分钟，现在我放弃了，帮助我...

好吧，错误指向第二个 @IBAction 方法，该方法向方法 func add(param1, param2, param3) 传递两个可选值。所以首先我认为 viewWillAppear 是在与 UIElements 建立连接后启动的。但这意味着我必须能够访问一些可重写的方法，并且在与 UIElements 建立连接之前启动。

这是一个好方法吗？另一个解决方案是在使用选项之前测试它们，但我知道如果您确定您的选项不包含 nil 值，您可以跳过此方法。

import UIKit

class ViewController: UIViewController {
    //The memory that will be reserved for computation
    var memoryValue1: Double!, memoryValue2: Double!, memoryValue3: Double!, memoryValue4: Double!

    var firstAttempt: Bool!

    //UIElemet Outlets
    @IBOutlet weak var outPutText: UILabel!

    override func viewWillAppear(animated: Bool) {
        memoryValue1 = 0.0
        firstAttempt = true
    }

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

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

    func add(value: Double, attempt: Bool, memory: Double){
        if attempt {
            self.firstAttempt = false
            self.memoryValue1 = value
            self.outPutText.text = String(value)
        } else {
            var newValue: Double = memory
            newValue = newValue + value
            self.outPutText.text = String(newValue)
        }
    }

    @IBAction func pressedC(sender: AnyObject) {
        outPutText.text = "0.0"
    }
    @IBAction func pressed1(sender: AnyObject) {
        add(1.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed2(sender: AnyObject) {
        add(2.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed3(sender: AnyObject) {
        add(3.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed4(sender: AnyObject) {
        add(4.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed5(sender: AnyObject) {
        add(5.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed6(sender: AnyObject) {
        add(6.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed7(sender: AnyObject) {
        add(7, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed8(sender: AnyObject) {
        add(8.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed9(sender: AnyObject) {
        add(9.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
    @IBAction func pressed0(sender: AnyObject) {
        add(0.0, attempt: self.firstAttempt, memory: self.memoryValue1)
    }
}

Answer 1

var memoryValue1: Double! 不是像 Java 中那样的引用类型。如果您尝试在它为零(null)时访问它，您的应用程序将会崩溃。当相关方法尝试将 memoryValue1 中包含的值传递给 add 方法时，Access 会包含类似 self.memoryValue1 的代码。

如果您改掉在所有属性声明末尾添加 ! 的习惯，您的学习过程将会大大增加。继续为此类属性赋值或使用 ? 代替。

您可以简单地分配:

var memoryValue1: Double = 0.0