ios - Segue 标识符崩溃问题

Question

这是我的 Storyboard和 homeSegue 标识符:



这是我返回上一个 viewController 的代码块:

-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{


    if([segue.identifier isEqualToString:@"homeSegue"]){
        ProductScannerViewController *product_scannerViewController = segue.destinationViewController;
        product_scannerViewController.delegate=self;

    }

    if([segue.identifier isEqualToString:@"scanSegue"]){

        [self.navigationController popToRootViewControllerAnimated:YES];

    }

}

它让我回到 ScanProductViewController。但是，当我尝试再次从 ScanProductViewController 中单击搜索按钮时，出现以下异常:

 2014-05-03 16:05:51.349 Spisrett[5239:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Product''
*** First throw call stack:
(
    0   CoreFoundation                      0x021d71e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib   

请建议我如何返回 ScanViewController 而不改变它以前的行为。

谢谢

这是它崩溃的方法..请建议:

-(void) configureFetchedResultsController:(NSString *) tableType;
 {
  //NSLog(@"This is the table tyoe");
  //NSLog(tableType);

tableType=@"Product";
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription 
                               entityForName:tableType inManagedObjectContext:self.context];
[fetchRequest setEntity:entity];
//Sorted by -Ishtiak
NSString *sortColumn=@"productTitle";



//actual sort.....  decidedShortingColumn


NSSortDescriptor *sort = [[NSSortDescriptor alloc]
                          initWithKey:sortColumn ascending:YES];


[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
[fetchRequest setFetchBatchSize:20];

NSFetchedResultsController *theFetchedResultsController = 
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                        managedObjectContext:self.context
                                        sectionNameKeyPath:nil 
                                               cacheName:nil];

fetchedResultsController = theFetchedResultsController;
fetchedResultsController.delegate = self;

}

Answer 1

奇怪的是，您使用 push segue 到 popToRootViewController。它不需要 segue 弹出或返回到以前的 View Controller 。