来自 rac_sequance 的 RACSignal 未正确传递信号

Question

我正在玩一些关于 Reactive Cocoa 的书中的代码，我被这本书困住了：这是我的照片导入程序代码：

+ (RACSignal *)importPhotos {
    NSURLRequest *request = [self popularURLRequest];

    return [[[[[[NSURLConnection rac_sendAsynchronousRequest:request] map:^id(RACTuple *value) {
        return [value second];
    }] deliverOn:[RACScheduler mainThreadScheduler]]
            map:^id(NSData *value) {
                id result = [NSJSONSerialization JSONObjectWithData:value
                                                            options:0
                                                              error:nil];
                return [[[result[@"photos"] rac_sequence] map:^id(NSDictionary *photoDictionary) {
                    FRPPhotoModel *photoModel = [FRPPhotoModel new];
                    [self configurePhotoModel:photoModel withDict:photoDictionary];
                    [self downloadThumbnailForPhotoModel:photoModel];

                    return photoModel;

                }] array];

            }] publish] autoconnect];
}

+ (void)configurePhotoModel:(FRPPhotoModel *)photoModel withDict:(NSDictionary *)dict {
    photoModel.photoName = dict[@"name"];
    photoModel.identifier = dict[@"id"];
    photoModel.photographerName = dict[@"user"][@"username"];
    photoModel.rating = dict[@"rating"];
    [[self urlForImageSize:3 inArray:dict[@"images"]] subscribeNext:^(id x) {
        photoModel.thumbnailURL = x;
    }];
 }

+ (RACSignal *)urlForImageSize:(NSInteger)size inArray:(NSArray *)array {
    return [[[[array rac_sequence] filter:^BOOL(NSDictionary *value) {
        return [value[@"size"] integerValue] == size;
    }] map:^id(NSDictionary *value) {
        return value[@"url"];
    }] signal];
}

+ (void)downloadThumbnailForPhotoModel:(FRPPhotoModel *)photoModel {
        [[RACObserve(photoModel, thumbnailURL) flattenMap:^RACStream *(id value) {
            return [self download:value];
        }] subscribeNext:^(id x) {
            photoModel.thumbnailData = x;
        }];
}
+ (RACSignal *)download:(NSString *)urlString {
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]];

    return [[NSURLConnection rac_sendAsynchronousRequest:request] map:^id(RACTuple *value) {
        return [value second];
    }];
}

和UI更新如下：

RAC(self.imageView, image) = [[RACObserve(self, photoModel.thumbnailData) filter:^BOOL(id value) {
    return value != nil;
}] map:^id(id value) {
    return [UIImage imageWithData:value];
}];

你能解释一下为什么我的 UI 没有更新或错误地更新了新的 UI 我从那个 NSData 对象获得的图像。

Answer 1

所以第一个问题是 flattenMap 在一些后台 RACScheduler 上交付。改为：

[[[[RACObserve(photoModel, thumbnailURL) ignore:nil] flattenMap:^RACStream *(id value) {
    return [self download:value];
}] deliverOn:[RACScheduler mainThreadScheduler]] subscribeNext:^(id x) {
    photoModel.thumbnailData = x;
}];

另一个问题是 download:nil 抛出一个错误，该错误没有被订阅者捕获，因此终止了提供观察值的信号。添加 ignore:nil 已修复的问题。

来自 rac_sequance 的 RACSignal 未正确传递信号

RACSignal from rac_sequance is not delivering signals correctly

objective-c

ios

reactive-cocoa