Question

I m a newbie to ObjC/Cocoa and Mac development in general, and toying with the basics.

狮子角的Xcode 4.2中新的可可应用的模拟缺省模板就是这样:

// AppDelegate.h
#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate>

@property (assign) IBOutlet NSWindow *window;

@end



// Appdelegate.m
#import "AppDelegate.h"

@implementation AppDelegate

@synthesize window = _window;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
}

@end

我先把这一基础作为各种实验的基础。阅读自动参考数字(该项目将使用)——,例如我假定,也许甚至可以(should)。替换<代码>assign <代码>NSWindow*window with weak,但似乎没有。

服用的是罚款,但在开张时用<条码>hang。图1:方案收到信号:“EXC_BAD_INSTRUCTION”,载于AppDelegate.m,其行文为@synthesizewindow;。

将限定语改为<代码>strong 进行方案工作,但我看不出从<条码>到<条码>到<条码>的意思。下面的印象是,非阿经共体/非经共体的配对物是分配/分配的,保留/保留。

一位经验更丰富的密码朋友建议,即使“weak 等成因window被过早地处理,而且有些准入尝试失败,该例外应当为EXC_BAD_ACCESS,而不是EXC_BAD_INSTRUCTION。

我在这里显然没有东西,但我不知道什么。

http://www.un.org。在对坠毁时间的 g果进行更仔细的研究之后,同一位朋友向我指出:,Mike Ash 的文章对此做了一些说明。由于我的理解之外的原因,NSWindow和其他一些高于retain和的类别。不能把提及不力作为目标。有趣的是,将财产申报改为这项工作:



@property (unsafe_unretained) IBOutlet NSWindow *window;

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/ chapters/ocProperties.html 申报不动产的 Apple果文件。

With that, a REVISED QUESTION:

What would be the proper way to go here? Stick to assign despite mentions around the web that it shouldn t be used with ARC? Go for strong? Keep using unsafe_unretained since it seems to work? Something else?

Answer 1

Conceptually, weak is the correct qualifier for a top-level IBOutlet on OS X (iOS is another story). However, to create a proper weak reference that zeroes on deallocation requires cooperation from the Objective C runtime. Classes that override retain or release break this support and so you can t create a weak reference to them. UIWindow is one such class.

因此,该模板使用了分配。也许,如果能够让非洲排雷中心,它应该真正使用不安全的同义词。无论在哪一种情况下,你都有一个简单的软弱提法,但这种提法并非零。

Answer 2

Mike Ash s blog discusses the issue with some Cocoa classes.

Look for it in the middle part of the page: Friday Q&A ARC. Look/Search for the text that starts with "ARC s implementation of zeroing weak references..."

问题是,有些班级没有处理......weak带出的零点。解决办法是采用ARC正常模板提供的assign<>。

Well, to answer the second question, even Apple s templates use assign for window when using ARC. So you may be safe for now. But your mileage may vary in the future.

Answer 3

, 具体地说是并不支持弱小的参考资料:这显然是因为它依赖压倒性保留和自行释放。

我预计,还有几起这样的 go道分散在遗留的科拉班上,这些 t似乎还没有记录——相反,你发现有一段错误。 (我预计这一点在某个时候也会成为汇编者警告)。)

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