ios - 为什么信号在 ReactiveCocoa 中被调用两次？

Question

我正在用 https://github.com/ReactiveCocoa/ReactiveCocoa 实现我的第一个代码.

用于登录用户。 [subscriber sendNext:user]; 行被调用了两次，但我希望只有一次。并且根本不调用 map (因此从不调用自动登录)

这是我的实现:

-(RACSignal *) login:(NSString *)email pwd:(NSString *)pwd
{
    DDLogInfo(@"Login user %@", email);

    RACSignal *login = [RACSignal createSignal:^ RACDisposable *(id<RACSubscriber> subscriber)
    {        
        [PFUser logInWithUsernameInBackground:email password:pwd block:^(PFUser *user, NSError *error) {

            if (error) {
                [subscriber sendError:error];
            } else {
                [subscriber sendNext:user];

                [subscriber sendCompleted];
            }
        }];

        return nil;
    }];

    [login map:^(PFUser *user) {
        return [self autoLogin:user];
    }];

    return login;
}

这样调用:

NSString *email = data[@"email"];
NSString *pwd = data[@"pwd"];
[SVProgressHUD showWithMaskType:SVProgressHUDMaskTypeBlack];

RACSignal *login = [[SyncEngine server] login:email pwd:pwd];

[login
 subscribeCompleted:^
{
    [[NSNotificationCenter defaultCenter]
     postNotificationName:NOTIFY_LOGIN_CHANGED
     object:self];

     [SVProgressHUD showSuccessWithStatus:LOC_OK];


     [self cancelForm];
}];

[login
 subscribeError:^(NSError *error)
{
    [SVProgressHUD dismiss];

    [AppUrls alertError:LOC_ERROR_LOGING msg:error.userInfo[@"error"]];
}];

Answer 1

发生这种情况是因为传递给 +[RACSignal createSignal:] 的 block 会在订阅信号时执行，并且您的代码会创建两个单独的订阅:

[login subscribeCompleted:^{ ... }];

[login subscribeError:^(NSError *error) { ... }];

如果只想创建单个订阅，请使用方法 -[RACSignal subscribeError:completed:]:

[login subscribeError:^(NSError *error) {
        [SVProgressHUD dismiss];

        [AppUrls alertError:LOC_ERROR_LOGING msg:error.userInfo[@"error"]];
    }
    completed:^{
        [[NSNotificationCenter defaultCenter]
         postNotificationName:NOTIFY_LOGIN_CHANGED
         object:self];

         [SVProgressHUD showSuccessWithStatus:LOC_OK];


         [self cancelForm];
    }];