ios - 如何使核心数据 ManagedObjectContext.ExecuteFetchRequest 同步而不是异步

Question

附件是我的代码。

给我问题的那一行是 let fetchRequest = try moc.executeFetchRequest(fetchRequest) as! [AppSettings] 似乎异步加载，但我希望它同步加载，以便我可以确保它正确检查用户名记录。

我该怎么做？

我知道它是异步加载的，因为当我不断地启动和停止程序时，它会在大约 80% 的时间内找到实体，而在随机的 20% 的时间内找不到实体。由于没有其他东西在改变实体(因为我只是不断地启动和停止程序)，所以当我使用命令

时，代码正在异步运行是有意义的

guard let appSettingsArrayItem = fetchRequest.first where fetchRequest.count>0 else {
                print ("no entities found...")
                return false
            }

有时找不到任何实体。

检查登录功能

func checkIfLoggedInAlready() -> Bool{
        let fetchRequest = NSFetchRequest(entityName: "AppSettings")
        //let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest) //Deletes ALL appsettings entities

        do {

            let fetchRequest = try moc.executeFetchRequest(fetchRequest) as! [AppSettings]

            guard let appSettingsArrayItem = fetchRequest.first where fetchRequest.count>0 else {
                print ("no entities found...")
                return false
            }

            guard let username = (appSettingsArrayItem as AppSettings).username else{
                print ("username not found")
                return false
            }

            print("number Of AppSetting Entities =\(fetchRequest.count)")
            print(username)

            //The following code deletes ALL the entities!
            //try moc.persistentStoreCoordinator!.executeRequest(deleteRequest, withContext: moc)

            //To delete just '1' entry use the code below.

            //moc.deleteObject(appSettingsArrayItem)
            //try moc.save()//save deletion change.

            //print("deleted particular entity item")

            return true
        } catch{
            fatalError("bad things happened \(error)")
        }


    }

整个 LoginViewController 包括检查登录功能

import UIKit
import CoreData

class LoginViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var usernameField: UITextField!
    @IBOutlet weak var passwordField: UITextField!

    var isLoggedIn = false

    let moc = DataController().managedObjectContext

    @IBAction func SignUpButtonPressed(sender: UIButton) {
        print("sign up")
    }

    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true
    }

    func textFieldShouldEndEditing(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true
    }


    override func viewDidLoad() {
        super.viewDidLoad()

        let tap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: "dismissKeyboard")
        view.addGestureRecognizer(tap)

        print("view loaded, check if already signed in here")

        let loggedIn = checkIfLoggedInAlready() //checks database to see

        if(loggedIn){
            print("was logged in!")
            isLoggedIn = true

            self.performSegueWithIdentifier("loginSegue", sender: self)
        }
    }

    func checkIfLoggedInAlready() -> Bool{
        let fetchRequest = NSFetchRequest(entityName: "AppSettings")
        //let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest) //Deletes ALL appsettings entities

        do {

            let fetchRequest = try moc.executeFetchRequest(fetchRequest) as! [AppSettings]

            guard let appSettingsArrayItem = fetchRequest.first where fetchRequest.count>0 else {
                print ("no entities found...")
                return false
            }

            guard let username = (appSettingsArrayItem as AppSettings).username else{
                print ("username not found")
                return false
            }

            print("number Of AppSetting Entities =\(fetchRequest.count)")
            print(username)

            //The following code deletes ALL the entities!
            //try moc.persistentStoreCoordinator!.executeRequest(deleteRequest, withContext: moc)

            //To delete just '1' entry use the code below.

            //moc.deleteObject(appSettingsArrayItem)
            //try moc.save()//save deletion change.

            //print("deleted particular entity item")

            return true
        } catch{
            fatalError("bad things happened \(error)")
        }


    }

    func dismissKeyboard() {
        //Causes the view (or one of its embedded text fields) to resign the first responder status.
        view.endEditing(true)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
        print("prepare seque")
    }

    func displayErrorMessage(errorMessage: String){
        print("show error console with Error:"+errorMessage)
        let alert = UIAlertController(title: "Error", message: errorMessage, preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }

    override func shouldPerformSegueWithIdentifier(identifier: String, sender: AnyObject?) -> Bool {
        switch(identifier){
            case "loginSegue":
                print("Is the user already logged in?")
                if(isLoggedIn){
                    print("Detected as YES")
                    return true
                }
                print("Detected as NO, so checking username and password fields next...")

                guard let password = passwordField.text!.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet()) where !password.isEmpty else {
                    displayErrorMessage("Password can not be empty!")
                    return false
                }

                guard let username = usernameField.text!.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet()) where !username.isEmpty else{
                    displayErrorMessage("Username can not be empty!")
                    return false
                }

                let url = "http://distribution.tech/restapi/v1/userlogin?email="+username+"&password="+password
                print(url)

                let json = JSON(url:url)
                print(json)

                if(json["status"].asInt==1){

                    let entity = NSEntityDescription.insertNewObjectForEntityForName("AppSettings", inManagedObjectContext: moc) as! AppSettings

                    entity.setValue(username, forKey: "username")
                    entity.setValue(password, forKey: "password")
                    entity.setValue(json["tokenid"].asString, forKey: "token")
                    entity.setValue(json["roleid"].asInt, forKey: "roleid")
                    entity.setValue(json["role"].asString, forKey: "role")
                    entity.setValue(json["companyid"].asInt , forKey: "companyid")
                    entity.setValue(json["isdev"].asInt, forKey: "isdev")

                    //save token and other details to database.
                    do {
                        try moc.save()
                        print("saved to entity")
                    }catch{
                        fatalError("Failure to save context: \(error)")
                    }

//                    token
//                    roleid int
//                    role
//                    companyid int
//                    
//                    {
//                        "companyid": 3,
//                        "userid": 2,
//                        "tokenid": "804febae26ddbd0292b3d2c66b30afd5028d5ba9",
//                        "status": 1,
//                        "roleId": 1,
//                        "role": "super_admin",
//                        "isdev": 0
//                    }

                    //Save to disk using our own method, as COREDATA is unreliable!

                    return true //login succesfull
                }else{
                    displayErrorMessage("Incorrect Username or Email")
                    return false//failed
                }

        default:
            displayErrorMessage("Unknown Error Related To Segue Not Found")
        }
      return false //if it gets to this point assume false
    }


}

托管对象在 DataController 中创建，其文件位于下方。

import UIKit
import CoreData

class DataController: NSObject {
    var managedObjectContext: NSManagedObjectContext
    override init() {
        // This resource is the same name as your xcdatamodeld contained in your project.
        guard let modelURL = NSBundle.mainBundle().URLForResource("AppSettings", withExtension:"momd") else {
            fatalError("Error loading model from bundle")
        }
        // The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
        guard let mom = NSManagedObjectModel(contentsOfURL: modelURL) else {
            fatalError("Error initializing mom from: \(modelURL)")
        }
        let psc = NSPersistentStoreCoordinator(managedObjectModel: mom)
        self.managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
        self.managedObjectContext.persistentStoreCoordinator = psc
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {
            let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
            let docURL = urls[urls.endIndex-1]
            /* The directory the application uses to store the Core Data store file.
            This code uses a file named "DataModel.sqlite" in the application's documents directory.
            */
            let storeURL = docURL.URLByAppendingPathComponent("AppSettings.sqlite")
            do {
                try psc.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: storeURL, options: nil)
            } catch {
                fatalError("Error migrating store: \(error)")
            }
        }
    }
}

有时会发生的实体和控制台错误的图像引用

实体和控制台在大多数情况下找到实体时的图像引用

Answer 1

ManagedObjectContext.ExecuteFetchRequest 已经同步运行，但看起来您正在后台优先线程中异步设置持久存储协调器。

如果此获取请求在应用启动时立即发生，并且您一遍又一遍地执行此操作，则有时可能无法完成设置。