ReactiveCocoa信号用于在观察认证状态时获取数据

Question

ReactiveCocoa相当新，我尝试构建一个信号，从远程API中异步获取某些资源，客户端必须首先对其进行身份验证。通过首先从API获取令牌，然后通过一些自定义HTTP头为每个后续请求传递它来处理身份验证。但是，在订阅fetchResource信号之后，可能会设置自定义标头，这在当前情况下会导致未经身份验证的请求。我想我实际上可以在self.authenticationStatus的subscribeNext块中构建请求，从而确保将设置令牌，但是我怎么能处理信号的处理呢？

- (RACSignal *)fetchResource
{
    return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        NSURLRequest *request = [self.requestSerializer
                                 requestWithMethod:@"GET"
                                 URLString:[[NSURL URLWithString:@"resource" relativeToURL:self.baseURL] absoluteString]
                                 parameters:nil error:nil];
        NSURLSessionDataTask *task = [self dataTaskWithRequest:request
                                      completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
            if (error) {
                [subscriber sendError:error];
            } else {
                [subscriber sendNext:responseObject];
                [subscriber sendCompleted];
            }
        }];

        // Actually trigger the request only once the authentication token has been fetched.
        [[self.authenticationStatus ignore:@NO] subscribeNext:^(id _) {
            [task resume];
        }];

        return [RACDisposable disposableWithBlock:^{
            [task cancel];
        }];
    }];
}

Answer 1

- (RACSignal *)fetchTokenWithCredentials:(Credentials *)credentials
{
    return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {

        // Fetch the token and send it to `subscriber`.
        Token *t = ... ;
        [subscriber sendNext:t];

        return nil;

    }];
}

- (RACSignal *)fetchResourceWithToken:(Token *)token
{
    return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {

        // Use `token` to set the request header. Then fetch
        // the resource and send it to `subscriber`. Basically
        // this part is what you already have.
        Resource *r = ... ;
        [subscriber sendNext:r];

        return nil;

    }];
}

在视图控制器中，如果您没有有效令牌，则显示模态验证对话框。当用户点击＆＃34;提交＆＃34;按钮，执行以下操作：

- (IBAction)handleAuthenticationSubmit:(id)sender
{
    Credentials *c = ... ;
    RACSignal *resourceSignal = [[[self fetchTokenWithCredentials:c]
            flattenMap:^(Token *t) {

                return [self fetchResourceWithToken:t];

            }]
            deliverOn:RACScheduler.mainThreadScheduler];

    [self rac_liftSelector:@selector(receiveResource:) withSignals:resourceSignal, nil];
}

- (void)receiveResource:(Resource *)resource
{
    [self.delegate authenticationController:self didReceiveResource:resource];
}