respondsToSelector和 instancesRespondToSelector的理解
2016-07-01 11:15
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respondsToSelector 和 instancesRespondToSelector是两个常用的方法,我们经常使用 someObject respondsToSelector,但是对于它和instancesRespondToSelector之间有什么区别?
首先先看两个方法的声明
我们可以以UIScreen来进行说明
测试代码
输出
说明:
从定义看,UIScreenMode *currentMode是一个实例属性
所以
同理
测试代码
输出
我们从中应该知道, 类 其实 也是一个兑现哥只是,是一个特殊对象!
首先先看两个方法的声明
@interface NSObject <NSObject> + (BOOL)instancesRespondToSelector:(SEL)aSelector; @end @protocol NSObject - (BOOL)respondsToSelector:(SEL)aSelector; @end
我们可以以UIScreen来进行说明
@interface UIScreen : NSObject <UITraitEnvironment> + (UIScreen *)mainScreen; @property(nullable,nonatomic,strong) UIScreenMode *currentMode @end
测试代码
UIScreen *screens = [UIScreen mainScreen]; if ([screens.class instancesRespondToSelector:@selector(currentMode)]){ NSLog(@"[screens.class instancesRespondToSelector:@selector(currentMode)]能响应"); } if ([screens respondsToSelector:@selector(currentMode)]){ NSLog(@"[screens respondsToSelector:@selector(currentMode)]能响应"); } if ([screens.class respondsToSelector:@selector(currentMode)]){ NSLog(@"[screens.class respondsToSelector:@selector(currentMode)]能响应"); } if ([UIScreen instancesRespondToSelector:@selector(currentMode)]){ NSLog(@"[UIScreen instancesRespondToSelector:@selector(currentMode)]能响应"); } if ([UIScreen respondsToSelector:@selector(currentMode)]){ NSLog(@"[UIScreen respondsToSelector:@selector(currentMode)]能响应"); }
输出
2016-06-30 16:17:24.501 TestNSlog[84989:2019395] [screens.class instancesRespondToSelector:@selector(currentMode)]能响应 2016-06-30 16:17:24.501 TestNSlog[84989:2019395] [screens respondsToSelector:@selector(currentMode)]能响应 2016-06-30 16:17:24.502 TestNSlog[84989:2019395] [screens.class respondsToSelector:@selector(currentMode)]不能响应 2016-06-30 16:17:26.181 TestNSlog[84989:2019395] [UIScreen instancesRespondToSelector:@selector(currentMode)]能响应 2016-06-30 16:17:26.181 TestNSlog[84989:2019395] [UIScreen respondsToSelector:@selector(currentMode)]不能响应
说明:
instancesRespondToSelector是一个类方法,用来判断该类的的实例(即对象)是否响应某个方法
respondsToSelector是一个实例(对象)方法,用来判断该实例(对象)是否响应某个方法
从定义看,UIScreenMode *currentMode是一个实例属性
所以
[screens.class instancesRespondToSelector:@selector(currentMode)]是能够响应的!!
[screens respondsToSelector:@selector(currentMode)]能响应
[screens.class respondsToSelector:@selector(currentMode)],由于screens.class得到的是 类本身,所以当然不能响应实例方法了
同理
[UIScreen respondsToSelector:@selector(currentMode)]不能响应!!!
测试代码
if ([screens.class instancesRespondToSelector:@selector(mainScreen)]){ NSLog(@"[screens.class instancesRespondToSelector:@selector(mainScreen)]能响应"); } else{ NSLog(@"[screens.class instancesRespondToSelector:@selector(mainScreen)]不能响应"); } if ([screens respondsToSelector:@selector(mainScreen)]){ NSLog(@"[screens respondsToSelector:@selector(mainScreen)]能响应"); } else{ NSLog(@"[screens respondsToSelector:@selector(mainScreen)]不能响应"); } if ([screens.class respondsToSelector:@selector(mainScreen)]){ NSLog(@"[screens.class respondsToSelector:@selector(mainScreen)]能响应"); } else{ NSLog(@"[screens.class respondsToSelector:@selector(mainScreen)]不能响应"); } if ([UIScreen instancesRespondToSelector:@selector(mainScreen)]){ NSLog(@"[UIScreen instancesRespondToSelector:@selector(mainScreen)]能响应"); } else{ NSLog(@"[UIScreen instancesRespondToSelector:@selector(mainScreen)]不能响应"); } if ([UIScreen respondsToSelector:@selector(mainScreen)]){ NSLog(@"[UIScreen respondsToSelector:@selector(mainScreen)]能响应"); } else{ NSLog(@"[UIScreen respondsToSelector:@selector(mainScreen)]不能响应"); }
输出
2016-06-30 16:27:44.244 TestNSlog[85085:2029436] [screens.class instancesRespondToSelector:@selector(mainScreen)]不能响应 2016-06-30 16:27:45.876 TestNSlog[85085:2029436] [screens respondsToSelector:@selector(mainScreen)]不能响应 2016-06-30 16:27:47.364 TestNSlog[85085:2029436] [screens.class respondsToSelector:@selector(mainScreen)]能响应 2016-06-30 16:27:51.156 TestNSlog[85085:2029436] [UIScreen instancesRespondToSelector:@selector(mainScreen)]不能响应 2016-06-30 16:27:53.372 TestNSlog[85085:2029436] [UIScreen respondsToSelector:@selector(mainScreen)]能响应
[screens.class instancesRespondToSelector:@selector(mainScreen)],由于mainScreen是类方法,这里判断实例是否响应,当然是不能响应!!
[screens respondsToSelector:@selector(mainScreen)],screens是一个实例(对象),这里判断它是否响应一个类方法,当然不能响应
[screens.class respondsToSelector:@selector(mainScreen)],screens.class是类本身,当然可以响应
我们从中应该知道, 类 其实 也是一个兑现哥只是,是一个特殊对象!
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