使用反应性可可检查 nil 模型？

Question

我想知道用反应可可检查 nil 值的方法是什么。

我假设我可以创建这样的信号。

// Turn state check into a signal to activate the rest
RACSignal* modelSignal = [self checkIfModelIsValid:self.model];

[[modelSignal then:^RACSignal *{
        return [self obtainImageSignal];
        // Always need to lazy call these functions
    }]
    subscribeNext:^(id x) {
        NSLog(@"It worked out! giving you null for fun though feel free to chain it? %@",x);
    }
    error:^(NSError *error) {
        // Replace with real ns error
        NSLog(@"Model or picture is nil: %@",error);
    } 
    completed:^{
        NSLog(@"Model this event started it all");
    }];

-(RACSignal *)obtainImageSignal {
    @weakify(self)
    RACSignal* imageSignal = [[NetworkManager sharedInstance] getImageWithImagePath:self.model.fullSizedPicture];

    // Processes that image signal
    [[imageSignal deliverOn:[RACScheduler mainThreadScheduler]]
         subscribeNext:^(UIImage* image) {
             @strongify(self)
             self.imageView.image = image;
             [self setUpTitle:self.model.title];
             [self setUpDescription:self.model.imageDescription];
         }
         error:^(NSError* error) {
             NSLog(@"Error: %@",[error description]);
         }
         completed:^{
             NSLog(@"Completed Operation: Image Retrieval Operation");
         }];

    return imageSignal;
}


-(RACSignal *) checkIfModelIsValid:(PhotoModel*) model {
    // Using then on this signal will force the image signal to handle the errors.?
    return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {

        if (self.model == nil || self.model.fullSizedPicture == nil) {
            [subscriber sendError:nil];
        }
        else {
            [subscriber sendNext:[NSNumber numberWithBool:YES]];
            [subscriber sendCompleted];
            // send complete for fun and see what it does
        }

        return nil;
    }];
}

或者是健全性检查不适用于反应函数式编程的情况？

Answer 1

只是为其他查看者举个例子，一种确保您没有从nil 模型中获取任何图像的方法 - 可以执行以下操作：

    RAC(self.someImageView, image) = [[RACObserve(self, model)
        filter:^BOOL(PhotoModel *currentModel) {
            return currentModel != nil;
        }]
        map:^id(PhotoModel *currentModel) {
            return [self someMethodToDownloadImageFromModel:currentModel];
        }];

请注意我是如何尝试避免在我的 RAC 块中使用 self 并避免注入在使用 subscribeNext:^、then:^ 等时发生的副作用。这样一来，您的代码就更易于管理，而且 RAC 更高。