FetchRequest在後續執行中返回重複結果

我在tabbarcontroller的第二個選項卡上設置了以下代碼。我第一次進入標籤時，正如我們所料，我的數據被正確提取。但是，如果我離開選項卡並返回，則獲取請求返回的array包含條目的兩倍。它返回的每個對象都是重複的。如果我離開選項卡並再次返回，則條目會再次複製，每個條目都有3個。我的請求有什麼問題會導致這種情況發生？FetchRequest在後續執行中返回重複結果

- (void)viewWillAppear:(BOOL)animated { 
    AppDelegate *delegate = (AppDelegate *)[[UIApplication sharedApplication] delegate]; 

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"EntityName" inManagedObjectContext:delegate.managedObjectContext]; 
    [fetchRequest setEntity:entity]; 

    // sort the results, since we want the most recent entry first 
    NSSortDescriptor *dateSort = [[NSSortDescriptor alloc] initWithKey:@"key" ascending:NO]; 
    NSArray *sortDescriptors = [NSArray arrayWithObject:dateSort]; 
    [fetchRequest setSortDescriptors:sortDescriptors]; 

    NSError *error; 
    NSMutableArray *array = [[delegate.managedObjectContext executeFetchRequest:fetchRequest error:&error] mutableCopy]; 
    NSLog(@"error %@",[error localizedDescription]); 
    self.fetchedObjects = [array copy]; 
    [array removeAllObjects]; 

    [self.tableView reloadData]; 
}

更新：我切換到NSFetchedResultsController這個固定我的問題。

來源

2012-08-05 Adam Johnson