// - weak & strong #define myWeakify(VAR) / try {} @finally {} / __weak __typeof__(VAR) VAR##_myWeak_ = (VAR)  #define myStrongify(VAR) / try {} @finally {} / __strong __typeof__(VAR) VAR = VAR##_myWeak_  #define myStrongifyRetVIfNil(VAR, RET) / try {} @finally {} / __strong __typeof__(VAR) VAR = VAR##_myWeak_;/ if(VAR == nil) return RET  #define myStrongifyRetNIfNil(VAR) / try {} @finally {} / __strong __typeof__(VAR) VAR = VAR##_myWeak_;/ if(VAR == nil) return 

- (void)handleFromVC {   NSArray *viewControllers = self.navigationController.viewControllers;   @myWeakify(self);   [viewControllers enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {     @myStrongifyRetNIfNil(self);     //代碼   }]; }