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[譯]Swift 2：可以使用 @NSManage 標(biāo)記自動(dòng)生成方法
原文鏈接
作者：Tomasz Szulc
原文日期：2015/08/06
譯者：mmoaay；校對(duì)：numbbbbb；定稿：shanks
Xcode 7 beta 5 中的 Swift 2 擁有另外一個(gè)特性：當(dāng)使用一對(duì)多關(guān)系時(shí)我們可以用
@NSManaged來(lái)聲明自動(dòng)生成方法。
這個(gè)技巧非常有用。假設(shè)你有一個(gè) Library 和多個(gè) Book 實(shí)體對(duì)象。且 Library 和 books 是一對(duì)多的關(guān)系。那么使用最新的 Xcode 和 @NSManaged 就可以在 Library 實(shí)體對(duì)象內(nèi)（手動(dòng)）聲明自動(dòng)生成方法。
就像下面這樣：
class Library: NSManagedObject {
@NSManaged func addBooksObject(book: Book)
@NSManaged func removeBooksObject(book: Book)
@NSManaged func addBooks(books: Set<Book>)
@NSManaged func removeBooks(books: Set<Book>)
}天哪，這種實(shí)現(xiàn)方式竟然如此優(yōu)雅！就在幾天前我還不得不從零開(kāi)始寫(xiě)這些方法。
但我發(fā)現(xiàn)一個(gè)問(wèn)題。我們確實(shí)可以像這樣聲明方法，但是問(wèn)題的關(guān)鍵是如何在任意位置生成它們并放入到 Entity+CoreDataProperties.swift 文件中？生成 Objective-C 子類時(shí)這些方法都會(huì)繼承，甚至在 Swift 項(xiàng)目中也是如此。然而，生成 Swift 語(yǔ)言時(shí)——這些方法竟然不見(jiàn)了！詳情參見(jiàn) rdar://22177139 。
下面的代碼是 Objective-C 生成的實(shí)體類
@interface Library (CoreDataGeneratedAccessors)
- (void)addBooksObject:(Book *)value;
- (void)removeBooksObject:(Book *)value;
- (void)addBooks:(NSSet<Book *> *)values;
- (void)removeBooks:(NSSet<Book *> *)values;
@end如果你將關(guān)系標(biāo)記為有序，就需要手動(dòng)聲明更多方法
- (void)insertObject:(Book *)value inBooksAtIndex:(NSUInteger)idx;
- (void)removeObjectFromBooksAtIndex:(NSUInteger)idx;
- (void)insertBooks:(NSArray<Book *> *)value atIndexes:(NSIndexSet *)indexes;
- (void)removeBooksAtIndexes:(NSIndexSet *)indexes;
- (void)replaceObjectInBooksAtIndex:(NSUInteger)idx withObject:(Book *)value;
- (void)replaceBooksAtIndexes:(NSIndexSet *)indexes withBooks:(NSArray<Book *> *)values;
- (void)addBooksObject:(Book *)value;
- (void)removeBooksObject:(Book *)value;
- (void)addBooks:(NSOrderedSet<Book *> *)values;
- (void)removeBooks:(NSOrderedSet<Book *> *)values;這樣寫(xiě)好麻煩啊……希望他們盡快修復(fù)這個(gè)問(wèn)題 :)
另一個(gè)等待 Apple 修復(fù)的問(wèn)題是：有序的一對(duì)多關(guān)系及其自動(dòng)生成的方法。這個(gè)問(wèn)題存在已久。但不知道是否有對(duì)應(yīng)的錯(cuò)誤報(bào)告。我認(rèn)為這個(gè)問(wèn)題發(fā)生在 Core Data 和下面這個(gè)方法第一次被釋放時(shí)。假設(shè)我們想給 Library 添加一些 Book
let ctx = self.managedObjectContext
let library = NSEntityDescription.insertNewObjectForEntityForName("Library", inManagedObjectContext: ctx) as! Library
let book1 = NSEntityDescription.insertNewObjectForEntityForName("Book", inManagedObjectContext: ctx) as! Book
library.addBooksObject(book1)結(jié)果是根本運(yùn)行不起來(lái)。
2015-08-06 23:14:18.541 NewNSManagedExample[54727:3677632] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSSet intersectsSet:]: set argument is not an NSSet'
*** First throw call stack:
(
0 CoreFoundation 0x00ea83b4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x005cde02 objc_exception_throw + 50
2 CoreFoundation 0x00dfc574 -[NSSet intersectsSet:] + 260
3 Foundation 0x00214756 NSKeyValueWillChangeBySetMutation + 153
4 Foundation 0x0017c4c7 NSKeyValueWillChange + 394
5 Foundation 0x0021466a -[NSObject(NSKeyValueObserverNotification) willChangeValueForKey:withSetMutation:usingObjects:] + 630
6 CoreData 0x00a981c6 _sharedIMPL_addObjectToSet_core + 182
7 CoreData 0x00a99189 __generateAccessor_block_invoke_2 + 41
8 NewNSManagedExample 0x000f0e80 _TFC19NewNSManagedExample11AppDelegate11applicationfS0_FTCSo13UIApplication29didFinishLaunchingWithOptionsGSqGVSs10DictionaryCSo8NSObjectPSs9AnyObject____Sb + 720
9 NewNSManagedExample 0x000f10c7 _TToFC19NewNSManagedExample11AppDelegate11applicationfS0_FTCSo13UIApplication29didFinishLaunchingWithOptionsGSqGVSs10DictionaryCSo8NSObjectPSs9AnyObject____Sb + 199
10 UIKit 0x0122e1c6 -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 337
11 UIKit 0x0122f56c -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 3727
12 UIKit 0x01236929 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1976
13 UIKit 0x01259af6 __84-[UIApplication _handleApplicationActivationWithScene:transitionContext:completion:]_block_invoke3142 + 68
14 UIKit 0x012336a6 -[UIApplication workspaceDidEndTransaction:] + 163
15 FrontBoardServices 0x03ff9ccc __37-[FBSWorkspace clientEndTransaction:]_block_invoke_2 + 71
16 FrontBoardServices 0x03ff97a3 __40-[FBSWorkspace _performDelegateCallOut:]_block_invoke + 54
17 FrontBoardServices 0x040171cb -[FBSSerialQueue _performNext] + 184
18 FrontBoardServices 0x04017602 -[FBSSerialQueue _performNextFromRunLoopSource] + 52
19 FrontBoardServices 0x040168fe FBSSerialQueueRunLoopSourceHandler + 33
20 CoreFoundation 0x00dc27af __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
21 CoreFoundation 0x00db843b __CFRunLoopDoSources0 + 523
22 CoreFoundation 0x00db7858 __CFRunLoopRun + 1032
23 CoreFoundation 0x00db7196 CFRunLoopRunSpecific + 470
24 CoreFoundation 0x00db6fab CFRunLoopRunInMode + 123
25 UIKit 0x01232f8f -[UIApplication _run] + 540
26 UIKit 0x01238724 UIApplicationMain + 160
27 NewNSManagedExample 0x000f24dc main + 140
28 libdyld.dylib 0x039afa21 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException這個(gè)問(wèn)題唯一的解決辦法就是重新實(shí)現(xiàn)那些方法。 詳情參見(jiàn)rdar://22177512——希望他們?cè)缛招迯?fù)這個(gè)問(wèn)題。
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