Coredata fetchrequest 谓词没有显示正确的东西

Posted 2023-03-13

【中文标题】Coredata fetchrequest 谓词没有显示正确的东西

【英文标题】：Coredata fetchrequest predicate doesn't show the right things

【发布时间】：2016-04-22 12:25:39

【问题描述】：

我是 swift 新手，我尝试使用 CoreData 制作应用程序，但谓词没有显示正确的结果。似乎程序忽略了谓词，因为没有谓词它显示相同的东西。 这是我的代码：

import UIKit

class UebungenAnzeigenTableViewController: UITableViewController 

var mgdContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

var uebungen = [Uebung]()

override func viewDidLoad() 
    super.viewDidLoad()



override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
    if let uvc = segue.destinationViewController as? UebungenAnzeigenViewController 
        if let identifier = segue.identifier
            switch identifier
                case "Brust":
                    let request = NSFetchRequest(entityName: "Uebung")

                    request.predicate = NSPredicate(format: "muskel == %@", "Brust")
                    do
                        try uebungen = mgdContext.executeFetchRequest(request) as! [Uebung]
                    
                    catch
                            print("Abfrage fehlgeschlagen!")
                    
                case "Ruecken":
                    break
                case "Beine":
                    break
                case "Schulter":
                    break
                case "Bizeps":
                    break
                case "Trizeps":
                    break
                case "Nacken":
                    break
                case "Unterarm":
                    break
            default:
                break
            
        
    

这里是应该展示练习的地方：

import UIKit

class UebungenAnzeigenViewController: UIViewController, UITableViewDelegate, UITableViewDataSource 

var mgdContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
@IBOutlet weak var tableView: UITableView!

var uebungen = [Uebung]()
    didSet
        self.tableView.reloadData()
    


override func viewDidLoad() 
    super.viewDidLoad()

    loadUebungen()




func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell 
    let cell = tableView.dequeueReusableCellWithIdentifier("UebungCell", forIndexPath: indexPath)
    let uebung = uebungen[indexPath.row]
    cell.textLabel!.text = uebung.name!
    cell.textLabel?.textAlignment = .Center
    return cell


func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int 
    return uebungen.count


func loadUebungen()
    let request = NSFetchRequest(entityName: "Uebung")
    do
        try uebungen = mgdContext.executeFetchRequest(request) as! [Uebung]
    
    catch
        print(error)
    




override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
    if segue.identifier == "neueUebung" 
        let ctrl = segue.destinationViewController as! UebungSaveViewController
        ctrl.saveDelegate = 
            (newUebung, newMuskelgruppe) in

            let neueUebung = NSEntityDescription.insertNewObjectForEntityForName("Uebung", inManagedObjectContext: self.mgdContext) as! Uebung
            neueUebung.name = newUebung
            neueUebung.muskel = newMuskelgruppe

            do
                try self.mgdContext.save()
            
            catch
                print("speichern fehlgeschlagen")
            
            self.loadUebungen()
            self.navigationController?.popViewControllerAnimated(true)
        
    

.. 我在这里保存了练习：

import UIKit

class UebungSaveViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource

var muskelgruppen = ["Brust", "Rücken", "Beine", "Schultern", "Bizeps", "Trizeps", "Nacken", "Unterarme"]
var saveDelegate: ((String, String) ->())?
var selectedMuskelgruppe = "Brust"

@IBOutlet weak var pickerView: UIPickerView!

@IBOutlet weak var nameTextField: UITextField!

@IBAction func saveUebungAction(sender: UIButton) 
    let neueUebung = nameTextField.text
    if saveDelegate != nil && neueUebung != nil 

        saveDelegate!(neueUebung!, selectedMuskelgruppe)

        
    


override func viewDidLoad() 
    super.viewDidLoad()
    self.pickerView.dataSource = self
    self.pickerView.delegate = self
    self.hideKeyboardWhenTappedAround()


func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int 
    return muskelgruppen.count


func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? 
    return muskelgruppen[row]


func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int 
    return 1


func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) 
    switch row
        case 0:
            selectedMuskelgruppe = "Brust"
        case 1:
            selectedMuskelgruppe = "Rücken"
        case 2:
            selectedMuskelgruppe = "Beine"
        case 3:
            selectedMuskelgruppe = "Schultern"
        case 4:
            selectedMuskelgruppe = "Bizeps"
        case 5:
            selectedMuskelgruppe = "Trizeps"
        case 6:
            selectedMuskelgruppe = "Nacken"
        case 7:
            selectedMuskelgruppe = "Unterarm"
    default:
        break
    

有人知道为什么这不起作用吗？我是 swift 新手，我尝试了很多东西，但我不明白..

【参考方案1】：

那是因为您似乎没有谓词：

func loadUebungen()
    let request = NSFetchRequest(entityName: "Uebung")
    do
        try uebungen = mgdContext.executeFetchRequest(request) as! [Uebung]
    
    catch
        print(error)
    

您确实有一个谓词的地方与实际填充表格的代码断开了连接，因此您获得了一个过滤列表，并且在 segue 方法（在前一个视图控制器中）中什么都不做，但随后没有应用谓词你真正需要它的地方（loadUebungen）。