線程1：EXC_BAD_INSTRUCTION（代碼= EXC_I386_INVOP，子碼= 0 * 0）錯誤

Question

我得到的錯誤：

1:EXC_BAD_INSTRUCTION(code=EXC_I386_INVOP,subcode=0*0)

我是新來的編碼和我下面這個視頻https://www.youtube.com/watch?v=Fv-A8lKn7VY

代碼如下：

import UIKit 
import CoreData 

class SwiftCoreDataHelper: NSObject { 

    class func directoryForDatabaseFilename()->NSString{ 
     return NSHomeDirectory().stringByAppendingString("/Library/Private Documents") 
    } 

    class func databaseFilename()->NSString{ 
     return "database.sqlite"; 
    } 

    class func managedObjectContext()->NSManagedObjectContext{ 


     do { try NSFileManager.defaultManager().createDirectoryAtPath(SwiftCoreDataHelper.directoryForDatabaseFilename() as String, withIntermediateDirectories: true, attributes: nil) } 
     catch { 
      print("Error Creating Directory for DB") 
     } 
     //  NSFileManager.defaultManager().createDirectoryAtPath(SwiftCoreDataHelper.directoryForDatabaseFilename(), withIntermediateDirectories: true, attributes: nil, error: &error) 

     let path:NSString = "\(SwiftCoreDataHelper.directoryForDatabaseFilename()) + \(SwiftCoreDataHelper.databaseFilename())" 

     let url:NSURL = NSURL(fileURLWithPath: path as String) 

     let managedModel:NSManagedObjectModel = NSManagedObjectModel.mergedModelFromBundles(nil)! 

     let storeCoordinator:NSPersistentStoreCoordinator = NSPersistentStoreCoordinator(managedObjectModel: managedModel) 

     do { 
     try storeCoordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil) 
     } 
     catch { 
      print("Error: \(error)") 
      } 

     let managedObjectContext = NSManagedObjectContext(concurrencyType: NSManagedObjectContextConcurrencyType.MainQueueConcurrencyType) 

     managedObjectContext.persistentStoreCoordinator = storeCoordinator 

     return managedObjectContext  
    } 

    class func insertManagedObject(className:NSString, managedObjectConect:NSManagedObjectContext)->AnyObject{ 

     let managedObject:NSManagedObject = NSEntityDescription.insertNewObjectForEntityForName(className as String, inManagedObjectContext: managedObjectConect) as NSManagedObject 

     return managedObject 

    } 

    class func saveManagedObjectContext(managedObjectContext:NSManagedObjectContext)->Bool{ 
     do { 
      try managedObjectContext.save() 
      return true 
     } catch _ { 
      return false 
     } 
    }  

    class func fetchEntities(className:NSString, withPredicate predicate:NSPredicate?, managedObjectContext:NSManagedObjectContext)->NSArray{ 
     let fetchRequest:NSFetchRequest = NSFetchRequest() 
     let entetyDescription:NSEntityDescription = NSEntityDescription.entityForName(className as String, inManagedObjectContext: managedObjectContext)! 

     fetchRequest.entity = entetyDescription 
     if (predicate != nil){ 
      fetchRequest.predicate = predicate! 
     } 

     fetchRequest.returnsObjectsAsFaults = false 
     var items = NSArray() 
     do { items = try managedObjectContext .executeFetchRequest(fetchRequest) 
     } catch { 
      print("Fetch Request Failed") 
     } 
     return items 
    } 
} 

在產生錯誤的代碼是：

let entetyDescription:NSEntityDescription = NSEntityDescription.entityForName(className as String, inManagedObjectContext: managedObjectContext)! 

我無法糾正錯誤。

Answer 1

entityForName返回可選值。它可能崩潰，因爲你強行解開這個操作與!

結果您可以使用可選在這種情況下，結合測試是否entityForName實際上返回一個值：

if let entityDescription = NSEntityDescription.entityForName(className as String, inManagedObjectContext: managedObjectContext) { 
    // work with entityDescription 
} else { 
    // handle the case in which entityForName returns nil 
}