respondsToSelector 外观代理失败

问题描述

我正在尝试通过在 [UIBarButtonItem 外观] 上运行 respondsToSelector 来检测 iOS 6 特定的外观方法.但是，无论我指定什么选择器，它总是为我返回 NO:

I’m trying to detect an iOS 6-specific appearance method, by running respondsToSelector on the [UIBarButtonItem appearance]. However, it always returns NO for me, whatever selector I specify:

// Should show NOPE in iOS 5, YEP in iOS 6. Shows NOPE always
NSLog(@"%@", [[UIBarButtonItem appearance] respondsToSelector:@selector(setBackgroundImage:forState:style:barMetrics:)] ? @"YEP" : @"NOPE"); 

// Should show YEP in both iOS 5 and iOS 6. Shows NOPE always
NSLog(@"%@", [[UIBarButtonItem appearance] respondsToSelector:@selector(setBackgroundImage:forState:barMetrics:)] ? @"YEP" : @"NOPE"); 

实际上，在它们各自的 iOS 版本上使用这些方法都可以正常工作，但我似乎无法检测到哪一个对我可用.那么我该如何正确地做到这一点呢?

Actually using those methods works fine on their respective versions of iOS, but I can’t seem to detect which one is available to me. So how do I properly do that?

推荐答案

不要检查外观代理.你永远不能依赖它，因为它是一个代理.相反，直接检查具有新方法的项目，在这种情况下，UIBarButtonItem:

Don't check the appearance proxy. You can never rely on that, since it's a proxy. Instead, directly check the item that has the new method, in this case, the UIBarButtonItem:

BOOL hasNewMethod = [UIBarButtonItem instancesRespondToSelector:@selector(setBackgroundImage:forState:style:barMetrics:)];
if( hasNewMethod )
  NSLog(@"Running iOS 6 with new method");
else
  NSLog(@"Current OS doesn't support method...");

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