复制NSMutableArray项

//copy players' info into playerList from a dictionary
playerList = [[NSMutableArray alloc] initWithArray:[params objectForKey:@"p"] copyItems:YES];

数组中的项实现copyWithZone,如下所示:

- (id)copyWithZone:(NSZone *)zone
{
   PlayerInfo* copy = [[[self class] allocWithZone:zone] init];
   [copy setNick:[self nick]];
   ...
   [copy setIsChallengedByMe:[self isChallengedByMe]];

   return copy;
}

然而,playerList似乎只有“超出范围”的对象。我做错什么了?