ios - 我从核心数据填充 PickerView 并得到错误 Index Out Of Range Swift 5

Question

我对 swift 非常陌生，我试图了解使用 CoreData 填充 UIPickerView。在观看了有关使用 UITableView 执行此操作的视频后，我为 UIPickerView 实现了相同的代码。代码工作正常，直到我从 CoreData 中删除所有内容，然后它因错误索引超出范围而崩溃。

我知道它崩溃的代码行，但我知道如何修复它。我在这里阅读了很多关于索引超出范围的问题，但我看不到任何相同的东西。

这是代码，表格 View 代码来自视频，我理解其中的 80%。

代码的崩溃行就在底部

import UIKit

import CoreData

// Global Variables and Constants

let appDelegate = UIApplication.shared.delegate as? AppDelegate

class ViewController: UIViewController {


    // Outlets
    @IBOutlet weak var tv: UITableView!

    @IBOutlet weak var pickerView: UIPickerView!

    // Varables
    var taskArray = [Task]()


    // Constants
    let cellid = "CellId"

    func randomNumber(num: Int) -> Int{
          return Int(arc4random_uniform(UInt32(num)))
    }

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


        callDelegates()
    }

    override func viewWillAppear(_ animated: Bool) {
        fetchyData()
        tv.reloadData()
        pickerView.reloadAllComponents()

    }

    func fetchyData(){
        fetchData { (done) in
            if done {
                if taskArray.count > 0 {
                    tv.isHidden = false
                    pickerView.isHidden = false
                } else {
                    tv.isHidden = true
                    pickerView.isHidden = true
                }
            }
        }
    }



    func callDelegates(){
        tv.delegate = self
        tv.dataSource = self
        tv.isHidden = true
        pickerView.dataSource = self
        pickerView.delegate = self
        pickerView.isHidden = self
    }



    @IBAction func btnPressedButton(_ sender: Any) {
                  //textLbl.text = "\(items)"
        pickerView.selectRow(randomNumber(num: 1000), inComponent: 0, animated: true)

    }

}

extension ViewController: UITableViewDataSource, UITableViewDelegate {

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return taskArray.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: cellid, for: indexPath) as! TableViewCell
        let task = taskArray[indexPath.row]
        cell.taskLbl.text = task.taskDescription
        if task.taskStatus == true {
            cell.backgroundColor = #colorLiteral(red: 0.3411764801, green: 0.6235294342, blue: 0.1686274558, alpha: 1)
            cell.taskLbl.textColor = #colorLiteral(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
        }

        return cell

    }
    func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        return true
    }

    func tableView(_ tableView: UITableView, editingStyleForRowAt indexPath: IndexPath) -> UITableViewCell.EditingStyle {
        return .none
    }
    func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath) -> [UITableViewRowAction]? {
        let deleteAction = UITableViewRowAction(style: .destructive, title: "Delete") { (action, indexPath) in
            self.deleteData(indexPath: indexPath)
            self.fetchyData()
            tableView.deleteRows(at: [indexPath], with: .automatic)
        }

        let taskStatusAction = UITableViewRowAction(style: .normal, title: "Completed") { (action, indexPath) in
            self.updateTaskStatus(indexPath: indexPath)
            self.fetchyData()
            tableView.reloadRows(at: [indexPath], with: .automatic)
        }
        taskStatusAction.backgroundColor = #colorLiteral(red: 0.7254902124, green: 0.4784313738, blue: 0.09803921729, alpha: 1)
        deleteAction.backgroundColor = #colorLiteral(red: 0.7450980544, green: 0.1568627506, blue: 0.07450980693, alpha: 1)

        return [deleteAction, taskStatusAction]
    }



}

extension ViewController {

    func fetchData(completion: (_ complete: Bool) -> ()) {
         guard let managedContext = appDelegate?.persistentContainer.viewContext else { return }
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Task")
        do {
            taskArray = try  managedContext.fetch(request) as! [Task]
            print("Data fetched, no issues")
            completion(true)
        } catch {
            print("Unable to fetch data: ", error.localizedDescription)
            completion(false)
        }

    }

    func deleteData(indexPath: IndexPath) {
         guard let managedContext = appDelegate?.persistentContainer.viewContext else { return }
        managedContext.delete(taskArray[indexPath.row])
        do {
            try managedContext.save()
            print("Data Deleted")

        } catch {
            print("Failed to delete data: ", error.localizedDescription)

        }
    }

    func updateTaskStatus(indexPath: IndexPath) {
        guard let managedContext = appDelegate?.persistentContainer.viewContext else { return }
        let task = taskArray[indexPath.row]
        if task.taskStatus == true {
            task.taskStatus = false
        } else {
            task.taskStatus = true
        }
        do {
            try managedContext.save()
            print("Data updated")

        } catch {
            print("Failed to update data: ", error.localizedDescription)

        }

    }

}
extension ViewController: UIPickerViewDelegate, UIPickerViewDataSource {


   func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {

        self.fetchyData()
        return taskArray.count
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {

        self.fetchyData()
        return taskArray[row].taskDescription.  //THE ERROR IS ON THIS LINE . Index Out OF Range//

    }

}

Answer 1

如果您遇到 outOfIndex 崩溃，请在访问数组中的元素之前检查
Swift 中的一个很好的方法:

 let isIndexValid = taskArray.indices.contains(row) 

  if isIndexValid {
   return taskArray[row].taskDescription

   } else {
       return "default text"
   }