respondsToSelector 和 instancesRespondToSelector是兩個常用的方法,我們經常使用 someObject respondsToSelector,但是對于它和instancesRespondToSelector之間有什么區別?
首先先看兩個方法的聲明
@interface NSObject <NSObject>
+ (BOOL)instancesRespondToSelector:(SEL)aSelector;
@end
@protocol NSObject
- (BOOL)respondsToSelector:(SEL)aSelector;
@end
我們可以以UIScreen來進行說明
@interface UIScreen : NSObject <UITraitEnvironment>
+ (UIScreen *)mainScreen;
@property(nullable,nonatomic,strong) UIScreenMode *currentMode
@end
測試代碼
UIScreen *screens = [UIScreen mainScreen];
if ([screens.class instancesRespondToSelector:@selector(currentMode)]){
NSLog(@"[screens.class instancesRespondToSelector:@selector(currentMode)]能響應");
}
if ([screens respondsToSelector:@selector(currentMode)]){
NSLog(@"[screens respondsToSelector:@selector(currentMode)]能響應");
}
if ([screens.class respondsToSelector:@selector(currentMode)]){
NSLog(@"[screens.class respondsToSelector:@selector(currentMode)]能響應");
}
if ([UIScreen instancesRespondToSelector:@selector(currentMode)]){
NSLog(@"[UIScreen instancesRespondToSelector:@selector(currentMode)]能響應");
}
if ([UIScreen respondsToSelector:@selector(currentMode)]){
NSLog(@"[UIScreen respondsToSelector:@selector(currentMode)]能響應");
}
輸出
2016-06-30 16:17:24.501 TestNSlog[84989:2019395] [screens.class instancesRespondToSelector:@selector(currentMode)]能響應
2016-06-30 16:17:24.501 TestNSlog[84989:2019395] [screens respondsToSelector:@selector(currentMode)]能響應
2016-06-30 16:17:24.502 TestNSlog[84989:2019395] [screens.class respondsToSelector:@selector(currentMode)]不能響應
2016-06-30 16:17:26.181 TestNSlog[84989:2019395] [UIScreen instancesRespondToSelector:@selector(currentMode)]能響應
2016-06-30 16:17:26.181 TestNSlog[84989:2019395] [UIScreen respondsToSelector:@selector(currentMode)]不能響應
說明: instancesRespondToSelector是一個類方法,用來判斷該類的的實例(即對象)是否響應某個方法
respondsToSelector 是一個實例(對象)方法,用來判斷該實例(對象)是否響應某個方法
從定義看,UIScreenMode *currentMode是一個實例屬性
所以[screens.class instancesRespondToSelector:@selector(currentMode)] 是能夠響應的!!
[screens respondsToSelector:@selector(currentMode)] 能響應
[screens.class respondsToSelector:@selector(currentMode)],由于screens.class得到的是 類本身,所以當然不能響應實例方法了
同理[UIScreen respondsToSelector:@selector(currentMode)]不能響應!!!
測試代碼
if ([screens.class instancesRespondToSelector:@selector(mainScreen)]){
NSLog(@"[screens.class instancesRespondToSelector:@selector(mainScreen)]能響應");
}
else{
NSLog(@"[screens.class instancesRespondToSelector:@selector(mainScreen)]不能響應");
}
if ([screens respondsToSelector:@selector(mainScreen)]){
NSLog(@"[screens respondsToSelector:@selector(mainScreen)]能響應");
}
else{
NSLog(@"[screens respondsToSelector:@selector(mainScreen)]不能響應");
}
if ([screens.class respondsToSelector:@selector(mainScreen)]){
NSLog(@"[screens.class respondsToSelector:@selector(mainScreen)]能響應");
}
else{
NSLog(@"[screens.class respondsToSelector:@selector(mainScreen)]不能響應");
}
if ([UIScreen instancesRespondToSelector:@selector(mainScreen)]){
NSLog(@"[UIScreen instancesRespondToSelector:@selector(mainScreen)]能響應");
}
else{
NSLog(@"[UIScreen instancesRespondToSelector:@selector(mainScreen)]不能響應");
}
if ([UIScreen respondsToSelector:@selector(mainScreen)]){
NSLog(@"[UIScreen respondsToSelector:@selector(mainScreen)]能響應");
}
else{
NSLog(@"[UIScreen respondsToSelector:@selector(mainScreen)]不能響應");
}
輸出
2016-06-30 16:27:44.244 TestNSlog[85085:2029436] [screens.class instancesRespondToSelector:@selector(mainScreen)]不能響應
2016-06-30 16:27:45.876 TestNSlog[85085:2029436] [screens respondsToSelector:@selector(mainScreen)]不能響應
2016-06-30 16:27:47.364 TestNSlog[85085:2029436] [screens.class respondsToSelector:@selector(mainScreen)]能響應
2016-06-30 16:27:51.156 TestNSlog[85085:2029436] [UIScreen instancesRespondToSelector:@selector(mainScreen)]不能響應
2016-06-30 16:27:53.372 TestNSlog[85085:2029436] [UIScreen respondsToSelector:@selector(mainScreen)]能響應
[screens.class instancesRespondToSelector:@selector(mainScreen)],由于mainScreen是類方法,這里判斷實例是否響應,當然是不能響應!!
[screens respondsToSelector:@selector(mainScreen)],screens是一個實例(對象),這里判斷它是否響應一個類方法,當然不能響應
[screens.class respondsToSelector:@selector(mainScreen)],screens.class是類本身,當然可以響應
我們從中應該知道, 類 其實 也是一個兌現哥只是,是一個特殊對象!
