Dynamic Method Resolution;动态添加方法:动态添加方法就是在消息转发前在`+ (BOOL)resolveInstanceMethod:(SEL)sel`方法中使用`class_addMethod()` 添加方法。

DynamicMethodResolution.m

void dynamicMethodIMP(id self, SEL _cmd) {
    // implementation ....
        printf("执行了dynamicMethodIMP!!!!");
}
//you can dynamically add it to a class as a method (called resolveThisMethodDynamically) using resolveInstanceMethod: like this:
@implementation MyClass
+ (BOOL)resolveInstanceMethod:(SEL)aSEL
{
    if (aSEL == @selector(resolveThisMethodDynamically)) {
          class_addMethod([self class], aSEL, (IMP) dynamicMethodIMP, "v@:");
          return YES;
    }
    return [super resolveInstanceMethod:aSEL];
}
@end
//performSelector:@selector(resolveThisMethodDynamically)];//输出:dynamicMethodIMP!!!!