ios – 了解RACSignal错误

我目前正在Reactive Cocoa中迈出第一步,并且我经历了一些陡峭的学习曲线来理解这些原理.

无论如何这里是我已经提出的.

我将NSArray属性绑定到RACSignal,以便能够通过网络对传入的JSON数据做出反应.

- (void)updateRandomUserData 
{
    @weakify(self);
    RAC(self, users) = [[self fetchRandomUserData] doNext:^(NSDictionary *json){
    @strongify(self);
    NSMutableArray *randomUsers = [NSMutableArray array];
        for (NSDictionary *dict in json[@"data"]) {
           BKRandomUser *randomUser = [MTLJSONAdapter modelOfClass:[BKRandomUser class] fromJSONDictionary:dict error:nil];
           [randomUsers addObject:randomUser];
        }

        self.users = randomUsers;
    }];
}

信号创建如下所示：

- (RACSignal *)fetchRandomUserData
{

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

      NSURLRequest *request = [NSURLRequest requestWithURL:url];

      AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
      [subscriber sendNext:JSON];
      } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON, NSError *error) {
        [subscriber sendError:error];
      }];

      [operation start];

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

      }] doError:^(NSError *error) {
        NSLog(@"error: %@", [error description]);
    }];

}

现在,当Web服务不提供任何我希望对此做出反应的数据时.现在应用程序崩溃了以下声明,我真的不明白：

* Terminating app due to uncaught exception ‘NSInternalInconsistencyException’, reason: ‘Received error from name: [[+createSignal:] -doError:] -doNext: in binding for key path “users” on : (null)’

我在这里错过了什么？

谢谢！

接受的答案将解决问题,但有一个更惯用,更优雅的方式来处理这个问题：

首先,使用-map：而不是使用-doNext：将JSON转换为用户数组：

RAC(self, users) = [[self fetchRandomUserData] map:^(NSDictionary *json){
    NSMutableArray *randomUsers = [NSMutableArray array];
    for (NSDictionary *dict in json[@"data"]) {
       BKRandomUser *randomUser = [MTLJSONAdapter modelOfClass:[BKRandomUser class] fromJSONDictionary:dict error:nil];
       [randomUsers addObject:randomUser];
    }

    return randomUsers;
}];

然后,要处理错误,您可以使用-catch ::

RAC(self, users) = [[[self fetchRandomUserData] map:^(NSDictionary *json){
    NSMutableArray *randomUsers = [NSMutableArray array];
    for (NSDictionary *dict in json[@"data"]) {
       BKRandomUser *randomUser = [MTLJSONAdapter modelOfClass:[BKRandomUser class] fromJSONDictionary:dict error:nil];
       [randomUsers addObject:randomUser];
    }

    return randomUsers;
}] catch:^(NSError *error) {
    return [RACSignal return:@[]];
}];

在此示例中,如果发生错误,我们会捕获它并将其替换为空数组.你可以做任何你想做的事.如果您只想忽略整个事情,请将其替换为nil或[RACSignal empty].或者调用另一个返回RACSignal *的方法.