-respondsToSelector:方法会查询消息的接收者所属的类是否有某消息的实现:
- 不论是否有声明
- 不论是它自己的, 还是它所继承的
因此, 它适用于检查一个类是否实现了其所遵守的协议所声明的
optional方法.
1 -respondsToSelector:仅关心某方法是否有实现, 而不关心它是否有声明
// MyClass.h
@interface MyClass : NSObject
- (void)aMethodWithDeclAndImpl;
- (void)aMethodWithDeclButWithoutImpl;
//- (void)aMethodWithoutDeclButWithImpl;
//- (void)aMethodWithoutDeclOrImpl;
@end
// MyClass.m
- (void)aMethodWithDeclAndImpl {
}
- (void)aMethodWithoutDeclButWithImpl {
}
@end
// main.m
int main(int argc, const char * argv[]) {
@autoreleasepool {
MyClass *instanceOfMyClass = [[MyClass alloc] init];
// 考察"声明的有无"和"实现的有无"对`-respondsToSelector:`返回结果的影响.
NSLog(@"can instance of MyClass respond to selector \"-aMethodWithDeclAndImpl\"?\t\t%@", [instanceOfMyClass respondsToSelector:@selector(aMethodWithDeclAndImpl)] ? @"YES" : @"NO");
NSLog(@"can instance of MyClass respond to selector \"-aMethodWithDeclButWithoutImpl\"?\t\t%@", [instanceOfMyClass respondsToSelector:@selector(aMethodWithDeclButWithoutImpl)] ? @"YES" : @"NO");
NSLog(@"can instance of MyClass respond to selector \"-aMethodWithoutDeclButWithImpl\"?\t\t%@", [instanceOfMyClass respondsToSelector:@selector(aMethodWithoutDeclButWithImpl)] ? @"YES" : @"NO");
NSLog(@"can instance of MyClass respond to selector \"-aMethodWithoutDeclOrImpl\"?\t\t%@", [instanceOfMyClass respondsToSelector:@selector(aMethodWithoutDeclOrImpl)] ? @"YES" : @"NO");
}
return 0;
}
输出结果:
can instance of MyClass respond to selector "-aMethodWithDeclAndImpl"? YES
can instance of MyClass respond to selector "-aMethodWithDeclButWithoutImpl"? NO
can instance of MyClass respond to selector "-aMethodWithoutDeclButWithImpl"? YES
can instance of MyClass respond to selector "-aMethodWithoutDeclOrImpl"? NO
即, 只要有实现, 不论是否有声明,
-respondsToSelector:都会返回YES.
2 -respondsToSelector:仅关心某方法是否有实现, 而不关心实现是来自于自己这个类型, 还是来自于继承
// BaseClass.h
@interface BaseClass : NSObject
- (void)aMethodLeftUnimplemented;
- (void)aMethodImplementedByBaseClass;
- (void)aMethodImplementedByBaseClassAndOverwrittenByDerivedClass;
@end
// BaseClass.m
@implementation BaseClass
- (void)aMethodImplementedByBaseClass {
}
- (void)aMethodImplementedByBaseClassAndOverwrittenByDerivedClass {
}
@end
// DerivedClass.h
@interface DerivedClass : BaseClass
- (void)aMethodImplementedByDerivedClass;
@end
// DerivedClass.m
@implementation DerivedClass
- (void)aMethodImplementedByBaseClassAndOverwrittenByDerivedClass {
}
- (void)aMethodImplementedByDerivedClass {
}
@end
// main.m
int main(int argc, const char * argv[]) {
@autoreleasepool {
DerivedClass *instanceOfDerivedClass = [[DerivedClass alloc] init];
NSLog(@"can instance of DerivedClass respond to selector \"-aMethodLeftUnimplemented\"?\t\t%@", [instanceOfDerivedClass respondsToSelector:@selector(aMethodLeftUnimplemented)] ? @"YES" : @"NO");
NSLog(@"can instance of DerivedClass respond to selector \"-aMethodImplementedByBaseClass\"?\t\t%@", [instanceOfDerivedClass respondsToSelector:@selector(aMethodImplementedByBaseClass)] ? @"YES" : @"NO");
NSLog(@"can instance of DerivedClass respond to selector \"-aMethodImplementedByBaseClassAndOverwrittenByDerivedClass\"?\t\t%@", [instanceOfDerivedClass respondsToSelector:@selector(aMethodImplementedByBaseClassAndOverwrittenByDerivedClass)] ? @"YES" : @"NO");
NSLog(@"can instance of DerivedClass respond to selector \"-aMethodImplementedByDerivedClass\"?\t\t%@", [instanceOfDerivedClass respondsToSelector:@selector(aMethodImplementedByDerivedClass)] ? @"YES" : @"NO");
}
return 0;
}
输出结果:
can instance of DerivedClass respond to selector "-aMethodLeftUnimplemented"? NO
can instance of DerivedClass respond to selector "-aMethodImplementedByBaseClass"? YES
can instance of DerivedClass respond to selector "-aMethodImplementedByBaseClassAndOverwrittenByDerivedClass"? YES
can instance of DerivedClass respond to selector "-aMethodImplementedByDerivedClass"? YES
即, 只要有实现, 不论是自己的实现还是继承得来的实现,
-respondsToSelector:都会返回YES.
