我正在设计一个应用程序，用户将在具有多个文本字段的警报视图中键入信息。然后将这些字符串组合并保存在实体（作为一个实体）的属性中。然后将其显示在表格视图中。
现在，如果用户输入错误，我将实现一种删除条目的方法。
我已经看到很多地方，他们说使用以下代码删除CoreData中的条目：
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath)
{
let managedObjectContext = coreData.persistentContainer.viewContext
if editingStyle == .delete
{
movieToDelete = fetchedResultController.object(at: indexPath)
let confirmDeleteAlertController = UIAlertController(title: "Remove Movie", message: "Are you sure you would like to delete \"\(movieToDelete!.title!)\" from your movie library?", preferredStyle: UIAlertControllerStyle.actionSheet)
let deleteAction = UIAlertAction(title: "Delete", style: UIAlertActionStyle.default, handler: { [weak self] (action: UIAlertAction) -> Void in
managedObjectContext.delete((self?.movieToDelete!)!)
self?.coreData.saveContext()
self?.movieToDelete = nil
})
let cancelAction = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.cancel, handler: { [weak self] (action: UIAlertAction) -> Void in
self?.movieToDelete = nil
})
confirmDeleteAlertController.addAction(deleteAction)
confirmDeleteAlertController.addAction(cancelAction)
present(confirmDeleteAlertController, animated: true, completion: nil)
}
}
但是，我正在关注youtube上的教程，因此我的代码中没有ManagedObjectContext来使用editingStyle.delete。现在我被困在如何删除条目上。我是否可以更改先前的代码以支持ManagedObjectContext，还是可以通过持久性容器删除条目？
这是我的viewController中的代码，我认为这对当前的问题很重要：
class ViewController: UITableViewController {
var alarmItems: [NSManagedObject] = []
let cellId = "cellId"
override func viewDidLoad() {
super.viewDidLoad()
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
let managedContext = appDelegate.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "AlarmItems")
do {
alarmItems = try managedContext.fetch(fetchRequest)
} catch let err as NSError {
print("Failed to fetch items", err)
}
}
@objc func addAlarmItem(_ sender: AnyObject) {
print("this works")
let alertController = UIAlertController(title: "Add New Item", message: "Please fill in the blanks", preferredStyle: .alert)
let saveAction = UIAlertAction(title: "Save", style: .default) { [unowned self] action in
//combined string of attributes
let myStrings: [String] = alertController.textFields!.compactMap { $0.text }
let myText = myStrings.joined(separator: ", ")
self.save(myText)
self.tableView.reloadData()
}
let cancelAction = UIAlertAction(title: "Cancel", style: .destructive, handler: nil)
alertController.addTextField { (textField) in
textField.placeholder = "Enter Name of Engineer"
}
alertController.addTextField { (textField) in
textField.placeholder = "Enter Date of Alarm in DD/MM/YYYY"
}
alertController.addTextField { (textField) in
textField.placeholder = "Enter Time of Alarm in 24h (eg: 2300)"
}
alertController.addTextField { (textField) in
textField.placeholder = "Please indicate True/False (type True or False)"
}
alertController.addTextField { (textField) in
textField.placeholder = "Insert comments (if any), or NIL"
}
alertController.addAction(saveAction)
alertController.addAction(cancelAction)
present(alertController, animated: true, completion: nil)
}
func save(_ itemName: String) {
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
let managedContext = appDelegate.persistentContainer.viewContext
let entity = NSEntityDescription.entity(forEntityName: "AlarmItems", in: managedContext)!
let item = NSManagedObject(entity: entity, insertInto: managedContext)
item.setValue(itemName, forKey: "alarmAttributes")
do {
try managedContext.save()
alarmItems.append(item)
} catch let err as NSError {
print("Failed to save an item", err)
}
}
@objc func exportCSV(_ sender: AnyObject) {
//will work on exporting csv in the future
return
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int{
return alarmItems.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath)
let alarmItem = alarmItems[indexPath.row]
cell.textLabel?.text = alarmItem.value(forKeyPath: "alarmAttributes") as? String
return cell
}
/*
//create delete feature
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath ) {
if editingStyle == UITableViewCell.EditingStyle.delete {
}
}
*/
}
答案 0 :(得分：0)
在使用NSFetchedResultsController时，删除数据源数组
var alarmItems: [NSManagedObject] = []
和alarmItems的所有其他出现。 NSFetchedResultsController实例成为数据源数组
在viewWillAppear中只是重新获取数据
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
do {
try fetchedResultsController.performFetch()
tableView.reloadData()
} catch {
print(error)
}
}
用
替换数据源和委托方法override func numberOfSections(in tableView: UITableView) -> Int {
return fetchedResultsController.sections?.count ?? 0
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let sectionInfo = fetchedResultsController.sections![section]
return sectionInfo.numberOfObjects
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath)
let alarmItem = fetchedResultsController.object(at: indexPath) as! NSManagedObject
cell.textLabel?.text = alarmItem.value(forKeyPath: "alarmAttributes") as? String
return cell
}
现在您的删除方法应该可以使用了。
注意：
我们鼓励您始终使用NSManagedObject子类AlarmItems（例如，每个Core Data记录在语义上表示一个AlarmItem）和点表示法。
let alarmItem = fetchedResultsController.object(at: indexPath) as! AlarmItem
cell.textLabel?.text = alarmItem.alarmAttributes