分段控制中的 NSArray 问题

发布于 2024-12-19 14:28:12 字数 1174 浏览 3 评论 0原文

我使用此示例来创建分段视图。在我的 viewDidLoad 方法中，我收到警告并且代码崩溃。

- (void)viewDidLoad {
    [super viewDidLoad];

    self.segmentedViewControllers = [self segmentedViewControllerContent];

    NSArray * segmentTitles = [self.segmentedViewControllers arrayByPerformingSelector:@selector(title)];

    self.segmentedControl = [[UISegmentedControl alloc] initWithItems:segmentTitles];
    self.segmentedControl.selectedSegmentIndex = 0;
    self.segmentedControl.segmentedControlStyle = UISegmentedControlStyleBar;

    [self.segmentedControl addTarget:self
                              action:@selector(didChangeSegmentControl:)
                    forControlEvents:UIControlEventValueChanged];

    self.navigationItem.titleView = self.segmentedControl;
    [self.segmentedControl release];

    [self didChangeSegmentControl:self.segmentedControl]; 
}

我在这一行收到警告：

NSArray * segmentTitles = [self.segmentedViewControllers arrayByPerformingSelector:@selector(title)];

NSArray 可能不会响应 arrayByPerformingSelector。

原文

I used this example to create a segmented view. In my viewDidLoad method I am getting a warning and code crashes.

- (void)viewDidLoad {
    [super viewDidLoad];

    self.segmentedViewControllers = [self segmentedViewControllerContent];

    NSArray * segmentTitles = [self.segmentedViewControllers arrayByPerformingSelector:@selector(title)];

    self.segmentedControl = [[UISegmentedControl alloc] initWithItems:segmentTitles];
    self.segmentedControl.selectedSegmentIndex = 0;
    self.segmentedControl.segmentedControlStyle = UISegmentedControlStyleBar;

    [self.segmentedControl addTarget:self
                              action:@selector(didChangeSegmentControl:)
                    forControlEvents:UIControlEventValueChanged];

    self.navigationItem.titleView = self.segmentedControl;
    [self.segmentedControl release];

    [self didChangeSegmentControl:self.segmentedControl]; 
}

I am getting a warning in this line:

NSArray * segmentTitles = [self.segmentedViewControllers arrayByPerformingSelector:@selector(title)];

that NSArray may not respond to arrayByPerformingSelector.

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

挽袖吟 2024-12-26 14:28:12

arrayByPerformingSelector: 不是发送到 NSArray 的有效消息。该方法可能位于原始代码使用的 NSArray 类别扩展之一中。检查您所关注的原始示例，并尝试查找 arrayByPerformingSelector: 的定义位置，然后在代码中#import 该文件。

回复收藏 0 原文

初见你 2024-12-26 14:28:12

arrayByPerformingSelector: 是有人编写的一种便利方法，以避免这样做：

NSMutableArray * tempArray = [NSMutableArray array];

for (id thing in things)
{
     [tempArray addObject:thing.name];
}
NSArray * namesOfthings = [tempArray copy];

但是，iOS 堆栈中已经有一些东西可以免费执行此操作！

NSArray * namesOfthings = [things valueForKeyPath:@"unionOfObjects.name"];

您可以在NSHipsters 博客文章中阅读有关 KVC 收集操作的更多信息。对于一个不起眼的 API 来说，它实际上非常有用。我很遗憾我花了这么长时间才找到它。

arrayByPerformingSelector: is a connivence method someone has written to avoid doing this:

NSMutableArray * tempArray = [NSMutableArray array];

for (id thing in things)
{
     [tempArray addObject:thing.name];
}
NSArray * namesOfthings = [tempArray copy];

However, there is already something in the iOS stack that will do this for free!

NSArray * namesOfthings = [things valueForKeyPath:@"unionOfObjects.name"];

You can read more about KVC collection operations in NSHipsters blog post. For an obscure API it's actually really useful. I am sad it took me this long to find it.

回复收藏 0 原文

~没有更多了~