+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        SEL systemSEL = @selector(sendAction:to:forEvent:);
        SEL replaceSEL = @selector(SG_sendAction:to:forEvent:);
        Method systemMethod = class_getInstanceMethod(self, systemSEL);
        Method replaceMethod = class_getInstanceMethod(self, replaceSEL);

        BOOL isAdd = class_addMethod(self, systemSEL, method_getImplementation(replaceMethod), method_getTypeEncoding(replaceMethod));

        if (isAdd) {
            class_replaceMethod(self, replaceSEL, method_getImplementation(systemMethod), method_getTypeEncoding(systemMethod));
        } else {
            // 添加失败，说明本类中有 replaceMethod 的实现，此时只需要将 systemMethod 和 replaceMethod 的IMP互换一下即可
            method_exchangeImplementations(systemMethod, replaceMethod);
        }
    });
}