Question

当我在iOS 8.3中执行这行代码时，这一行崩溃了：

NSArray *results = [self executeFetchRequest:request inContext:context];

这是整个函数失败：

+ (id) executeFetchRequestAndReturnFirstObject:(NSFetchRequest *)request inContext:(NSManagedObjectContext *)context
{
    [request setFetchLimit:1];

    NSArray *results = [self executeFetchRequest:request inContext:context];
    if ([results count] == 0)
    {
        return nil;
    }
    return [results objectAtIndex:0];
}

上述函数由：

调用

+ (id)findFirstByAttribute:(NSString *)attribute withValue:(id)searchValue inContext:(NSManagedObjectContext *)context
{   
    NSFetchRequest *request = [self requestFirstByAttribute:attribute withValue:searchValue inContext:context];
    [request setPropertiesToFetch:[NSArray arrayWithObject:attribute]];

    return [self executeFetchRequestAndReturnFirstObject:request inContext:context];
}

值得注意的是，我对iOS编程非常陌生，所以请放轻松我，问题可能不是最好的，可能没有太多支持代码，但这是由于我在iOS上缺乏知识。我的android问题通常比这更好：P如果我能够添加更多细节，我会尽可能多地添加，崩溃日志在下面

*由于未捕获的异常终止应用＆＃39; NSInvalidArgumentException＆＃39;，原因：＆＃39;错误提取请求   （NSManagedObjectResultType与内容不兼容   propertiesToFetch）＆＃39;   * 第一次抛出调用堆栈：（0 CoreFoundation 0x0000000111d7dc65 exceptionPreprocess + 165 1 libobjc.A.dylib
  0x0000000110fafbb7 objc_exception_throw + 45 2 CoreData
  0x00000001112ecb6e - [NSSQLGenerator   newSQLStatementForRequest：ignoreInheritance：countOnly：nestingLevel：] +   1646 3 CoreData 0x00000001112d8dc4    - [NSSQLAdapter _statementForFetchRequest：ignoreInheritance：countOnly：nestingLevel：] + 244 4 CoreData 0x00000001111f0e0c    - [NSSQLAdapter _newSelectStatementWithFetchRequest：ignoreInheritance：] + 316 5 CoreData 0x00000001111f0a86 - [NSSQLCore newRowsForFetchPlan：] + 118 6 CoreData 0x00000001111f033c - [NSSQLCore objectsForFetchRequest：inContext：] +   524 7 CoreData 0x00000001111efdbb    - [NSSQLCore executeRequest：withContext：error：] + 299 8 CoreData 0x00000001112caa6c __65- [NSPersistentStoreCoordinator   executeRequest：withContext：error：] _ block_invoke + 3356 9 CoreData
  0x00000001112d3c30 gutsOfBlockToNSPersistentStoreCoordinatorPerform +   192 10 libdispatch.dylib 0x0000000114e29614   _dispatch_client_callout + 8 11 libdispatch.dylib 0x0000000114e0f002 _dispatch_barrier_sync_f_invoke + 365 12 CoreData   0x00000001112c5245 _perform + 197 13 CoreData
  0x00000001111efa58 - [NSPersistentStoreCoordinator   executeRequest：withContext：error：] + 504 14 CoreData
  0x00000001111ee2ca - [NSManagedObjectContext   executeFetchRequest：error：] + 586 15 HawkExpress
  0x000000010e52438e + [NSManagedObject（MagicalRecord）   executeFetchRequest：inContext：] + 62 16 HawkExpress
  0x000000010e52446e + [NSManagedObject（MagicalRecord）   executeFetchRequestAndReturnFirstObject：inContext：] + 78 17   HawkExpress 0x000000010e5261fc   + [NSManagedObject（MagicalRecord）findFirstByAttribute：withValue：inContext：] + 140 18 HawkExpress
  0x000000010e526274 + [NSManagedObject（MagicalRecord）   findFirstByAttribute：withValue：] + 100 19 HawkExpress
  0x000000010e52aa54 + [FavouritesManager doesFavouriteExist：] + 84 20   HawkExpress 0x000000010e4de4a7    - [BookCabViewController tableView：cellForRowAtIndexPath：] + 2087 21 UIKit 0x00000001124b9a28 - [UITableView   _createPreparedCellForGlobalRow：withIndexPath：willDisplay：] + 508 22 UIKit 0x0000000112498248 - [UITableView   _updateVisibleCellsNow：isRecursive：] + 2853 23 UIKit 0x00000001124ae8a9 - [UITableView layoutSubviews] + 210 24 UIKit
  0x0000000112438a2b - [UIView（CALayerDelegate）layoutSublayersOfLayer：]   + 536 25 QuartzCore 0x000000010fdfbec2 - [CALayer layoutSublayers] + 146 26 QuartzCore 0x000000010fdf06d6 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE +   380 27 QuartzCore 0x000000010fdf0546   _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24 28 QuartzCore 0x000000010fd5c886   _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 242 29 QuartzCore 0x000000010fd5da3a   _ZN2CA11Transaction6commitEv + 462 30 QuartzCore 0x000000010fd5e0eb   _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 89 31 CoreFoundation 0x0000000111cb0ca7   __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION + 23 32 CoreFoundation 0x0000000111cb0c00   __CFRunLoopDoObservers + 368 33 CoreFoundation 0x0000000111ca6a33 __CFRunLoopRun + 1123 34 CoreFoundation
  0x0000000111ca6366 CFRunLoopRunSpecific + 470 35图形服务
  0x0000000114a34a3e GSEventRunModal + 161 36 UIKit
  0x00000001123b8900 UIApplicationMain + 1282 37 HawkExpress
  0x000000010e4baa23 main + 99 38 libdyld.dylib
  0x0000000114e5d145 start + 1）libc ++ abi.dylib：终止于   NSException（lldb）
类型的未捕获异常

Answer 1

在进行计数之前，您需要检查NSArray结果是否为零。

if (array != nil) {
    NSUInteger count = [array count]; // May be 0 if the object has been deleted.
    //
}
else {
    // Deal with error.
}

请参阅https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html

Answer 2

尝试将[request setPropertiesToFetch:[NSArray arrayWithObject:attribute]];行注释掉？

'错误提取请求（NSManagedObjectResultType与propertiesToFetch的内容不兼容）'表示您似乎期望默认NSFetchRequestResultType（NSManagedObjectResultType）。但是你要求不要获取完整的实体，而只是 ONE 属性（为什么，顺便提一下？你的方法提供了一个期望的值，只提供了一个属性来获取）。

我的解决方案：

- (id)findEntityNamed:(NSString*)entity withKeyPath:(NSString*)path equalTo:(id)value
{
    NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setEntity:[NSEntityDescription entityForName:entity
                                    inManagedObjectContext:context]];

    NSPredicate* predicate = 
    [NSComparisonPredicate predicateWithLeftExpression:[NSExpression expressionForKeyPath:path]
                                   rightExpression:[NSExpression expressionForConstantValue:value]
                                          modifier:NSDirectPredicateModifier
                                              type:NSEqualToPredicateOperatorType
                                           options:0];

    [fetchRequest setPredicate:predicate];
    [fetchRequest setFetchLimit:1];            // ONLY 1 OBJECT IS FETCHED!

    NSError* err = nil;
    NSArray* results = [context executeFetchRequest:fetchRequest error:&err];
    [fetchRequest release];

    if( err )
    {
        // do logging stuff etc.
    }

    if( [results count] < 1 )
        return nil;

    return [results lastObject];
}

你可以尝试这个，并告诉你这是否更像你正在寻找

Answer 3

您的NSFetchRequest对象可能未正确构造。

这是一个有效的NSFetchRequest示例。通过googling＆＃34; NSFetchRequest示例＆＃34;找到更多信息。

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == %@", aTitle]; //<----- (a)
[request setEntity:[NSEntityDescription entityForName:@"Person" inManagedObjectContext:moc]]; 
[request setPredicate:predicate];

注意（a），字符串必须严格遵循谓词格式字符串模式（请参阅NSPrediate类引用），name必须是托管对象模型中Person实体的属性

问题在于这部分

NSFetchRequest *request = [self requestFirstByAttribute:attribute withValue:searchValue inContext:context]; 
[request setPropertiesToFetch:[NSArray arrayWithObject:attribute]];

所以，如果仍未解决，请发布方法[self requestFirstByAttribute ...]的代码。

iOS崩溃与核心数据

3 个答案: