Question

我目前正在尝试使用UISearchBar和Core Data实现一个简单的搜索功能，我在此函数中遇到错误“无法分配给属性：“ ItemArray”是仅获取属性”，如果有人可以帮助解决该错误，并且还建议了另一种实现搜索的简单方法，这将非常有帮助。

func loadItems(with request: NSFetchRequest<Item>) {
    let request : NSFetchRequest<Item> = Item.fetchRequest()

    do {
        itemArray = try context.fetch(request)
    } catch {
        print("Error fetching data from context")
    }
    tableView.reloadData()
}


}

这是整个文件：

import UIKit
import CoreData



class TodoListViewController: UITableViewController {

var itemArray: [Item] { return Array(self.category.items!) as! [Item] }


let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

var category: Category!


override func viewDidLoad() {
    super.viewDidLoad()

    print(FileManager.default.urls(for: .documentDirectory, in: .userDomainMask))


}

@IBOutlet weak var todoTableView: UITableView!

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return itemArray.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCell(withIdentifier: "ToDoItemCell", for: indexPath)


    let item = itemArray[indexPath.row]

    cell.textLabel?.text = item.title

    cell.accessoryType = item.done ? .checkmark : .none

    return cell

}



override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    //print(itemArray[indexPath.row])

    itemArray[indexPath.row].done = !itemArray[indexPath.row].done

    saveItems()

    tableView.deselectRow(at: indexPath, animated: true)

}


@IBAction func addButtonPressed(_ sender: UIBarButtonItem) {

    var textField = UITextField()

    let alert = UIAlertController(title: "Add New Todoey Item", message: "", preferredStyle: .alert)

    let action = UIAlertAction(title: "Add Item", style: .default) { [weak self] (action) in
        guard let self = self else { return }

        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        let newItem = Item(context: self.context)
        newItem.title = textField.text!
        self.category.addToItems(newItem)

        self.saveItems()

    }

    alert.addTextField { (alertTextField) in
        alertTextField.placeholder = "Create new item"
        textField = alertTextField
        print(alertTextField.text)
    }


alert.addAction(action)

self.present(alert, animated: true, completion: nil)

}

func saveItems() {

    do {
       try context.save()
    } catch {
        print("Error saving context")
    }

    self.tableView.reloadData()
}

func loadItems(with request: NSFetchRequest<Item>) {
    let request : NSFetchRequest<Item> = Item.fetchRequest()

    do {
        itemArray = try context.fetch(request)
    } catch {
        print("Error fetching data from context")
    }
    tableView.reloadData()
}


}

extension TodoListViewController: UISearchBarDelegate {
    func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {

    let request : NSFetchRequest<Item> = Item.fetchRequest()
   request.predicate = NSPredicate(format: "title CONTAINS[cd] %@", searchBar.text!)


    request.sortDescriptors = [NSSortDescriptor(key: "title", ascending: true)]

    loadItems(with: request)

  tableView.reloadData()


}

Answer 1

itemArray被声明为只读属性，这正是错误所言。

一种解决方案是将属性声明为空数组

var itemArray = [Item]()

并在loadItems中呼叫viewDidLoad()

override func viewDidLoad() {
    super.viewDidLoad()
    loadItems()
    print(FileManager.default.urls(for: .documentDirectory, in: .userDomainMask))
}

loadItems中的参数没有意义，请忽略它。

func loadItems() { ... }

如果要获取特定Category的商品，请在NSPredicate中添加适当的loadItems

无法分配给属性：“ itemArray”是仅获取属性

1 个答案: