Question

我想在我的RSS阅读器中创建一个“收藏夹”。我的RSS解析器正在解析NSMutableArray的RSS提要，然后从我的部分rss（选定的帖子）创建对象“item”。我的代码：

//Creating mutable array and adding items:

    - (void)viewDidLoad {
        if (favoritedAlready == nil) {
            favoritedAlready = [[NSMutableArray alloc] init];
            [[NSUserDefaults standardUserDefaults] setObject:favoritedAlready forKey:@"favorites"];
            [[NSUserDefaults standardUserDefaults] synchronize];
            NSLog(@"избранное с нуля");
        }
    }
    - (void) addToFavorites {
        NSMutableArray* favoritedAlready = [[NSUserDefaults standardUserDefaults] objectForKey:@"favorites"];
        [favoritedAlready addObject: item];
        [[NSUserDefaults standardUserDefaults] setObject:favoritedAlready forKey:@"favorites"];
        [[NSUserDefaults standardUserDefaults] synchronize];

        NSLog(@"Добавлено в избранное. В избранном %i статей", [favoritedAlready count]);
    }

    //Removing items (another View)
    - (void)viewWillAppear:(BOOL)animated {
        [super viewWillAppear:animated];
        rssItems = [[NSUserDefaults standardUserDefaults] objectForKey:@"favorites"];
        [self.tableView reloadData];
        NSLog(@"Загрузилось избранное, %i избранных статей", [rssItems count]);
    }
    - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
        NSLog(@"Номерок строчки в которой удаляемый объект %i", indexPath.row+1);
        [rssItems removeObjectAtIndex:indexPath.row];
        [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];

        [[NSUserDefaults standardUserDefaults] setObject:rssItems forKey:@"favorites"];
        [[NSUserDefaults standardUserDefaults] synchronize];
    }

最初效果很好，但是当我添加和删除项目时，它开始崩溃。崩溃日志：我将对象添加到收藏夹并将其删除：

2011-09-25 20:14:44.534 ARSSReader[36211:11303] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x015505a9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x016a4313 objc_exception_throw + 44
    2   CoreFoundation                      0x01508ef8 +[NSException raise:format:arguments:] + 136
    3   CoreFoundation                      0x01508e6a +[NSException raise:format:] + 58
    4   CoreFoundation                      0x01547dd1 -[__NSCFArray removeObjectAtIndex:] + 193
    5   ARSSReader                          0x000a0ced -[FavoritesView tableView:commitEditingStyle:forRowAtIndexPath:] + 173
    6   UIKit                               0x00876037 -[UITableView(UITableViewInternal) animateDeletionOfRowWithCell:] + 101
    7   UIKit                               0x0080b4fd -[UIApplication sendAction:to:from:forEvent:] + 119
    8   UIKit                               0x0089b799 -[UIControl sendAction:to:forEvent:] + 67
    9   UIKit                               0x0089dc2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
    10  UIKit                               0x0089c7d8 -[UIControl touchesEnded:withEvent:] + 458
    11  UIKit                               0x0082fded -[UIWindow _sendTouchesForEvent:] + 567
    12  UIKit                               0x00810c37 -[UIApplication sendEvent:] + 447
    13  UIKit                               0x00815f2e _UIApplicationHandleEvent + 7576
    14  GraphicsServices                    0x01c91992 PurpleEventCallback + 1550
    15  CoreFoundation                      0x01531944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    16  CoreFoundation                      0x01491cf7 __CFRunLoopDoSource1 + 215
    17  CoreFoundation                      0x0148ef83 __CFRunLoopRun + 979
    18  CoreFoundation                      0x0148e840 CFRunLoopRunSpecific + 208
    19  CoreFoundation                      0x0148e761 CFRunLoopRunInMode + 97
    20  GraphicsServices                    0x01c901c4 GSEventRunModal + 217
    21  GraphicsServices                    0x01c90289 GSEventRun + 115
    22  UIKit                               0x00819c93 UIApplicationMain + 1160
    23  ARSSReader                          0x00001e79 main + 121
    24  ARSSReader                          0x00001df5 start + 53
)
terminate called throwing an exception(gdb)

但是，如果我添加了项目，重新启动了应用程序，然后将其删除，则效果非常好。

我添加了商品，重新启动了应用，删除了商品，并尝试添加新商品：

2011-09-25 20:19:19.212 ARSSReader[36461:11303] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray insertObject:atIndex:]: mutating method sent to immutable object'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x015505a9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x016a4313 objc_exception_throw + 44
    2   CoreFoundation                      0x01508ef8 +[NSException raise:format:arguments:] + 136
    3   CoreFoundation                      0x01508e6a +[NSException raise:format:] + 58
    4   CoreFoundation                      0x01547cf1 -[__NSCFArray insertObject:atIndex:] + 209
    5   CoreFoundation                      0x01544c14 -[__NSCFArray addObject:] + 68
    6   ARSSReader                          0x00004b35 -[DetailsViewController addToFavorites] + 149
    7   UIKit                               0x0080b4fd -[UIApplication sendAction:to:from:forEvent:] + 119
    8   UIKit                               0x00a1dcc3 -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 156
    9   UIKit                               0x0080b4fd -[UIApplication sendAction:to:from:forEvent:] + 119
    10  UIKit                               0x0089b799 -[UIControl sendAction:to:forEvent:] + 67
    11  UIKit                               0x0089dc2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
    12  UIKit                               0x0089c7d8 -[UIControl touchesEnded:withEvent:] + 458
    13  UIKit                               0x0082fded -[UIWindow _sendTouchesForEvent:] + 567
    14  UIKit                               0x00810c37 -[UIApplication sendEvent:] + 447
    15  UIKit                               0x00815f2e _UIApplicationHandleEvent + 7576
    16  GraphicsServices                    0x01c91992 PurpleEventCallback + 1550
    17  CoreFoundation                      0x01531944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    18  CoreFoundation                      0x01491cf7 __CFRunLoopDoSource1 + 215
    19  CoreFoundation                      0x0148ef83 __CFRunLoopRun + 979
    20  CoreFoundation                      0x0148e840 CFRunLoopRunSpecific + 208
    21  CoreFoundation                      0x0148e761 CFRunLoopRunInMode + 97
    22  GraphicsServices                    0x01c901c4 GSEventRunModal + 217
    23  GraphicsServices                    0x01c90289 GSEventRun + 115
    24  UIKit                               0x00819c93 UIApplicationMain + 1160
    25  ARSSReader                          0x00001e79 main + 121
    26  ARSSReader                          0x00001df5 start + 53
)
terminate called throwing an exception(gdb)

Answer 1

在addToFavorites

NSMutableArray* favoritedAlready = [[NSUserDefaults standardUserDefaults] objectForKey:@"favorites"];

将返回一个NSArray（保存一个可变版本没有区别），而不是NSMutableArray

您需要创建一个可变版本：

NSMutableArray* favoritedAlready = [[[NSUserDefaults standardUserDefaults] objectForKey:@"favorites"] mutableCopy];

显然，您不能将项目添加到不可变数组中。同样只是将返回值强制转换为NSMutableArray是错误的，它可能有用，也可能没有，但这是无关紧要的。

Answer 2

问题是NSUserDefaults只返回不可变数组，即使你放入一个可变数组：

特别注意事项：返回的数组及其内容是不可变的，即使您最初设置的值是可变的。

因此，当您从NSUserDefaults获取数组时，您必须使用可变复制方法或使用返回的NSArray创建新的NSMutableArray来转换它。

<小时/> 您可能希望将更改合并到NSUserDefaults的更少方法调用 - 可能是批量生成，也许是在某些时间间隔。让本地数组跟踪更改，然后写出更改，而不是首先从 NSUserDefaults获取数组。这将节省一次磁盘行程，并使您的代码更高效。

NSMutableArray添加/删除对象+ NSUserDefaults

2 个答案: