Objective-C NSMutableArray removeObjectAtIndex : crashes

Question

我有一个带有表格 View 的 View Controller ，您可以在其中删除单元格。我有另一个处理称为书签的类，该类称为 BookmarkHandler .有一些方法可以上传书签、获取整个书签数组和删除书签。下面是这个类:

+ (NSMutableArray *)bookmarkCollection {

NSMutableArray *bookmarkCollection = [[NSUserDefaults standardUserDefaults] objectForKey: @"bookmarks"];

if (!bookmarkCollection) {

    bookmarkCollection = [[NSMutableArray alloc] init];
}

return bookmarkCollection;
}

+ (void)deleteBookmark: (NSIndexPath *)indexPath {

    NSMutableArray *bookmarkCollection = [[NSUserDefaults standardUserDefaults] objectForKey: @"bookmarks"];

    [bookmarkCollection removeObjectAtIndex: indexPath.row];

    [[NSUserDefaults standardUserDefaults] setObject:bookmarkCollection forKey: @"bookmarks"];

    [[NSUserDefaults standardUserDefaults] synchronize];

}
+ (void)uploadBookmark:(NSDictionary *)singleBookmark {

    NSMutableArray *bookmarkCollection = [[NSUserDefaults standardUserDefaults] objectForKey: @"bookmarks"];


if (!bookmarkCollection) {

    bookmarkCollection = [[NSMutableArray alloc] init];
} 

NSMutableDictionary *bookmark1 = [[NSMutableDictionary alloc] initWithDictionary: singleBookmark];

NSMutableDictionary *bookmark2 = [[NSMutableDictionary alloc] initWithDictionary: singleBookmark];


NSNumber *number1 = [[NSNumber alloc] initWithInt: 1];
NSNumber *number2 = [[NSNumber alloc] initWithInt: 2];

[bookmark1 setObject:number1 forKey: @"bookmarkTag"];
[bookmark2 setObject:number2 forKey: @"bookmarkTag"];

[bookmarkCollection addObject: bookmark1];
[bookmarkCollection addObject: bookmark2];

[[NSUserDefaults standardUserDefaults] setObject:bookmarkCollection forKey: @"bookmarks"];

[[NSUserDefaults standardUserDefaults] synchronize];

}

书签集合是一个可变数组，由具有名称和日期对象/键的字典填充。这些名称和日期是填充另一个 View Controller 中表格 View 单元格标题的内容。表格 View 中的单元格数量由 [[BookmarkHandler bookmarkCollection] count]; 决定。

在另一个 View Controller 中，您可以删除表格 View 单元格，所以我要做的是实现委托(delegate)方法:

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {


if (editingStyle == UITableViewCellEditingStyleDelete) {

    [BookmarkHandler deleteBookmark: indexPath]; 

    [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject: indexPath] withRowAnimation:UITableViewRowAnimationLeft];
}
}

所以，当我删除一个单元格时，我会从 BookmarkHandler 中删除一个书签。调用 deleteBookmark:并从 TableView 中删除该行。但有时这条线上会出现崩溃:

        [bookmarkCollection removeObjectAtIndex: indexPath.row];

但是没有崩溃日志，我添加了一个 All Exceptions 断点。

有什么我做错了吗？感谢帮助...

Answer 1

问题在这里:

NSMutableArray *bookmarkCollection = [[NSUserDefaults standardUserDefaults] objectForKey: @"bookmarks"];

NSUserDefaults 不保存可变数组，它只是将它保存为 NSArray。
所以获取它的可变副本:

NSMutableArray *bookmarkCollection = [[[NSUserDefaults standardUserDefaults] objectForKey: @"bookmarks"] mutableCopy];