我已经建立了一个应用程序(我的第一个),它的工作方式就像我想要的一样,但后来我需要向它添加CoreData来让我的事件被保存fetched。我可以看到我的事件(添加信息到tableviewremove信息从那里)得到保存,因为我打印它,和应用程序是 "Loaded "在 "viewDidAppear".问题我认为是我保存数组,而不是NSobject。或者我是在获取数组,而不是NSobject?我相信我需要做的是将我的数组添加到一个NSManagedObject中?像这样。
var List:[MealsMenu] = [].当我这样做的时候,我得到了它的工作!这很好!但是,我有一个VC,它可以把我的数组添加到NSManagedObject中。但是,我有一个VC在UIPickerView中调用这个变量,当我把列表添加到NSManagedObject(MealsMenu,这是我在coredatamodel中的实体)时,我得到了这个错误信息。
Cannot convert return expression of type 'NSManagedObject' to return type 'String?
我已经尝试在谷歌上搜索了几天,但在我的案例中找不到任何解决方案。你们有谁知道我可以做什么吗?
我的实体(MealsMenu)有一个属性叫 "餐点",它是指字符串。
正如我所说的,如果我跳过PickerView所在的VC,我就可以让它工作了!我的实体(MealsMenu)有一个叫做 "餐点 "的属性,它是指字符串。添加和删除的事件都被保存了。
以下是我的代码:(所有写着 "List[row]"或 "List[indexPath.row]"的地方我都得到了这个错误信息)。
addViewController.tableViewController:(所有的地方都写着 "List[row]"或 "List[indexPath.row]",我得到这个错误信息)。
import UIKit
import CoreData
class addViewController: UIViewController, UITextFieldDelegate {
var context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
@IBOutlet weak var input: UITextField!
@IBAction func addToMenu(_ sender: Any) {
if input != nil{
let newMeal = NSEntityDescription.insertNewObject(forEntityName: "MealsMenu", into: context)
newMeal.setValue(self.input.text, forKey: "meals")
do {
try context.save()
print("SAVED")
}
catch{
print(error)
}
input.text = ""
}else{
print("That's not a meal!")
}
}
override func viewDidLoad() {
super.viewDidLoad()
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
self.view.endEditing(true)
}
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
input.resignFirstResponder()
return true
}
}
tableViewController:
import UIKit
import CoreData
class tableViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return (List.count)
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell(style: .default, reuseIdentifier: "cell")
cell.textLabel?.text = List[indexPath.row]
cell.textLabel?.textColor = UIColor.white
cell.backgroundColor = UIColor.clear
return(cell)
}
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
if editingStyle == UITableViewCell.EditingStyle.delete
{
List.remove(at: indexPath.row)
myTableView.reloadData()
}
}
@IBOutlet weak var myTableView: UITableView!
override func viewDidAppear(_ animated: Bool) {
myTableView.reloadData()
}
override func viewDidLoad() {
super.viewDidLoad()
coredataClass.saveItems()
coredataClass.loadData()
}
}
ViewController: tableViewController:
import UIKit
import CoreData
var List:[MealsMenu] = []
class ViewController: UIViewController {
@IBOutlet weak var monday: UITextField!
@IBOutlet weak var tuesday: UITextField!
@IBOutlet weak var wednesday: UITextField!
@IBOutlet weak var thursday: UITextField!
@IBOutlet weak var friday: UITextField!
@IBOutlet weak var saturday: UITextField!
@IBOutlet weak var sunday: UITextField!
var daysArray = [UITextField]()
let pickerView = ToolbarPickerView()
var selectedMenu : String?
override func viewDidLoad() {
super.viewDidLoad()
setupDelegateForPickerView()
setupDelegatesForTextFields()
coredataClass.loadData()
}
func setupDelegatesForTextFields() {
//appending textfields in an array
daysArray += [monday, tuesday, wednesday, thursday, friday, saturday, sunday]
//using the array to set up the delegates, inputview for pickerview and also the inputAccessoryView for the toolbar
for day in daysArray {
day.delegate = self
day.inputView = pickerView
day.inputAccessoryView = pickerView.toolbar
}
}
func setupDelegateForPickerView() {
pickerView.dataSource = self
pickerView.delegate = self
pickerView.toolbarDelegate = self
}
}
// Create an extension for textfield delegate
extension ViewController : UITextFieldDelegate {
func textFieldDidBeginEditing(_ textField: UITextField) {
self.pickerView.reloadAllComponents()
}
}
// Extension for pickerview and toolbar
extension ViewController : UIPickerViewDelegate, UIPickerViewDataSource {
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
return List.count
}
func numberOfComponents(in pickerView: UIPickerView) -> Int {
return 1
}
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
return List[row]
}
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
// Check if the textfield isFirstResponder.
if monday.isFirstResponder {
monday.text = List[row]
} else if tuesday.isFirstResponder {
tuesday.text = List[row]
} else if wednesday.isFirstResponder {
wednesday.text = List[row]
} else if thursday.isFirstResponder {
thursday.text = List[row]
} else if friday.isFirstResponder {
friday.text = List[row]
} else if saturday.isFirstResponder {
saturday.text = List[row]
} else if sunday.isFirstResponder {
sunday.text = List[row]
} else {
//log errors
}
}
}
extension ViewController: ToolbarPickerViewDelegate {
func didTapDone() {
self.view.endEditing(true)
}
func didTapCancel() {
self.view.endEditing(true)
}
}
具体来说,"ViewController "中的这些函数行会抛出这样的错误:Cannot convert return expression of type 'MealsMenu' to return type 'String'?
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
return List[row]
}
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
// Check if the textfield isFirstResponder.
if monday.isFirstResponder {
monday.text = List[row]
} else if tuesday.isFirstResponder {
tuesday.text = List[row]
} else if wednesday.isFirstResponder {
wednesday.text = List[row]
} else if thursday.isFirstResponder {
thursday.text = List[row]
} else if friday.isFirstResponder {
friday.text = List[row]
} else if saturday.isFirstResponder {
saturday.text = List[row]
} else if sunday.isFirstResponder {
sunday.text = List[row]
} else {
//log errors
}
}
而在 "tableViewController "中,这个函数也抛出了类似的错误:Cannot assign value of type 'MealsMenu' to type 'String'?
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell(style: .default, reuseIdentifier: "cell")
cell.textLabel?.text = List[indexPath.row]
cell.textLabel?.textColor = UIColor.white
cell.backgroundColor = UIColor.clear
非常感谢任何指导和帮助!
安德烈亚斯
请仔细阅读错误信息,然后看看你的设计。
您的数据源是一个数组 MealsMenu
实例的子类,它是 NSManagedObject
而返回值的类型是 String?
.
这就是错误信息的内容。你不能返回一个 MealsMenu
字符串的实例
return List[row].meals
数据源声明行有两个不好的做法。
后者会清楚地表明该变量包含多个项目,例如
var menus : [MealsMenu] = []
经过这样的改变,再加上把这一行一分为二,错误就更明显了。
let menu = menus[row]
return menu.meals
对了,命名 meals
也是很混乱的,因为它意味着是一个数组。
在 cellForRow
改行
let menu = menus[indexPath.row]
cell.textLabel?.text = menu.meals