oc methodForSelector与instanceMethodForSelector区别

- (IMP)methodForSelector:(SEL)aSelector
如果接受者是一个类对象，则返回类对象的方法；
如果接受者是一个实例对象，则返回实例对象的方法；

+ (IMP)instanceMethodForSelector:(SEL)aSelector
返回一个对应aSelector的实例方法
下面是个demo

#import <Foundation/Foundation.h>

@interface ATest : NSObject
@property (nonatomic, strong) NSDictionary *hiDIc;
- (void)sayHi;
+ (void)sayHi;
@end

#import "ATest.h"

@implementation ATest
- (void)sayHi{
    NSLog(@"instance say hi=%@;",self.hiDIc);
}
+ (void)sayHi{
    NSLog(@"class say hi");
}
@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"Hello, World!");
        ATest *test = [[ATest alloc]init];
        test.hiDIc = @{};
        SEL sel = NSSelectorFromString(@"sayHi");
        IMP mp = [test methodForSelector:sel];
        void(*mp1)(id,SEL) = (void*)mp;
        mp1(test,sel);
        
        mp = [ATest methodForSelector:sel];
        void(*mp2)(id,SEL) = (void*)mp;
        mp2(test,sel);
        
        mp = [ATest instanceMethodForSelector:sel];
        void(*mp3)(id,SEL) = (void*)mp;
        mp3(test,sel);
        
        
    }
    return 0;
}

运行结果如下：

2018-09-11 20:36:54.962026+0800 Test1[73782:1635537] Hello, World!

2018-09-11 20:36:54.962480+0800 Test1[73782:1635537] instance say hi={

};

2018-09-11 20:36:54.962941+0800 Test1[73782:1635537] class say hi

2018-09-11 20:36:54.963015+0800 Test1[73782:1635537] instance say hi={

};