按下按钮时创建新数组

Question

我想每次按下按钮（ActionButton）时创建一个新数组。第一次按下此按钮时，应创建一个新数组并添加 10。当第二次按下按钮时，应创建另一个新数组并添加 20。依此类推。我还想将创建的数组保存在核心数据中。 在这种情况下，发生了指定的错误。但是当从

let

更改为

var

时，它就只有 1 个数组，并且每次都会被覆盖，对吗？ 您能否善意地告诉我哪些代码适合创建一个新数组，添加当前值并保存它。

import UIKit
import CoreData

class ViewController: UIViewController {

    var number : Double = 0
    
    //  Reference to Managed Object Context
    let context = (UIApplication.shared.delegate as!     AppDelegate).persistentContainer.viewContext

    var average : Stats?
    var array : Stats?
    
//-------------------------------------------------------------------------------------
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        fetchStats()
        
    }
//-------------------------------------------------------------------------------------
    @IBAction func ActionButton(_ sender: UIButton) {

        number += 10.0
        average?.value = number
        
        //Idea
        let newarray = [Double]()
        newarray.append(number)
        array?.new = newarray
        
        //Error message by .append:
            //Cannot use mutatingChange 'let' to 'var' to make it mutable member on                                            immutable value: 'TestArray' is a 'let' constant
            //Change 'let' to 'var' to make it mutable
        
        
        saveData()
    
    }
    
//-------------------------------------------------------------------------------------
    func fetchStats() {
        
    //Fetch the data from CoreData to display in the View
    do {
        if let found = try context.fetch(Stats.fetchRequest()).first {
            average = found
            number = found.value
            
            array = found
            newarray = found.new
            
        } else {
            average = Stats(context: context)
            average?.value = 0
            
            array = Stats(context: context)
            array?.new = []
            
            saveData()
        }
                    
    }
    catch {
        print(error)
        }
    }
//-------------------------------------------------------------------------------------
    func saveData() {
        do {
            try context.save()
        } catch {
            print(error)
        }
    }
}

Answer 1

不清楚为什么你想要多个单元素数组，但假设你有一个有效的理由......

您想使用“数组的数组”。每次点击按钮，您都会将一个新数组附加到“数组的数组”中：

class ViewContoller: UIViewController {
    
    var number : Double = 0
    var theArrays: [[Double]] = []
    
    @IBAction func ActionButton(_ sender: UIButton) {
        
        number += 10.0
        theArrays.append([number])
        
        print() // blank line

        for i in 0..<theArrays.count {
            print("Array \(i):", theArrays[i])
        }

        print() // blank line

        print("theArrays:", theArrays)

        print() // blank line
        print("-----------")
    }

}

如果点击按钮 4 次，您将在调试控制台中看到以下内容：

Array 0: [10.0]

theArrays: [[10.0]]

-----------

Array 0: [10.0]
Array 1: [20.0]

theArrays: [[10.0], [20.0]]

-----------

Array 0: [10.0]
Array 1: [20.0]
Array 2: [30.0]

theArrays: [[10.0], [20.0], [30.0]]

-----------

Array 0: [10.0]
Array 1: [20.0]
Array 2: [30.0]
Array 3: [40.0]

theArrays: [[10.0], [20.0], [30.0], [40.0]]

-----------