【发布时间】：2016-03-25 16:12:36
【问题描述】：
下面附上我的代码。
给我带来问题的行是 let fetchRequest = try moc.executeFetchRequest(fetchRequest) as! [AppSettings] 似乎是异步加载，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，因为当我不断启动和停止程序时，它大约有 80% 的时间会找到实体，而随机有 20% 的时间不会。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），因此代码异步运行是有道理的，所以当我使用命令时
guard let appSettingsArrayItem = fetchRequest.first where fetchRequest.count>0 else {
print ("no entities found...")
return false
}
它有时会找不到任何实体。
查看登录功能
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)")
}
}
}
}
有时可能发生的实体和控制台错误的图像参考
实体和控制台大部分时间找到实体时的图像参考
【问题讨论】：
-
基本上强烈建议不要为结果提供与获取请求相同的变量名称。
executeFetchRequest确实同步工作。 -
它是同步的。如果不是，会有一些机制让您知道它何时完成（委托、阻止、通知......）。
-
任何想法为什么它有时会得到实体，有时如果它是同步的，有时不会？真的很困惑可能是什么原因造成的。
-
@vadian 我什至没有注意到我使用了相同的变量名很好的捕获，想知道这是否会导致任何奇怪的错误，只是为了更好的形式而改变。
标签： ios core-data asynchronous swift2 synchronous