ReactiveCocoa捕获所有错误 - 对集合对象的异步网络操作

我刚刚开始学习reactivecocoa.我想对集合对象中的每个条目执行网络操作并解析返回结果,如果报告错误,则将该条目标记为无效.

以下示例说明了该问题.urlList数组有4个条目.2个条目生成错误(生成连接关闭和超时错误).因此不会通知所有条目的订阅块.

- (RACSignal *)processStationList
{
    NSArray *urlList = @[@"http://66.55.93.205/listen.pls",@"http://84.20.77.50:8000/listen.pls",@"http://valekalter.serverroom.us:9264/listen.pls", @"http://66.55.93.205:8080/listen.pls"];

    return [RACSignal createSignal:^RACDisposable *(id subscriber) {
        [[urlList.rac_sequence.signal flattenMap:^RACStream *(NSString *urlString) {
            NSLog(@"flatten map %@",urlString);
            return [self fetchStationURLListForStation:urlString];
        }] subscribeNext:^(id x) {
            NSLog(@"suscribe next %@",x);
            [subscriber sendNext:x];
        } error:^(NSError *error) {
            NSLog(@"suscribe error %@",error);
            [subscriber sendNext:nil];
        } completed:^{
            NSLog(@"completed");
            [subscriber sendCompleted];
        }];
        return nil;
    }];
}
    - (RACSignal *)fetchStationURLListForStation:(NSString *)urlString
    {
        NSURL *url = [NSURL URLWithString:urlString];
        NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
        return [[NSURLConnection rac_sendAsynchronousRequest:urlRequest] map:^(RACTuple *value) {

        // for simplicity i have commented the following method which parses the .pls data to extract the
       // URL List and returing hard coded URL list
       //  return [self processStationURLData:[value second]];
          return @[@"http://66.55.93.205",@"http://66.55.93.205"];
        }];
    }

输出:

2014-01-27 10:49:27.108 Playground[6566:1303] flatten map http://66.55.93.205/listen.pls
2014-01-27 10:49:27.112 Playground[6566:1303] flatten map http://84.20.77.50:8000/listen.pls
2014-01-27 10:49:27.120 Playground[6566:1303] flatten map http://valekalter.serverroom.us:9264/listen.pls
2014-01-27 10:49:27.121 Playground[6566:1303] flatten map http://66.55.93.205:8080/listen.pls
2014-01-27 10:49:27.641 Playground[6566:3603] suscribe next (
    "http://66.55.93.205:80/"
)
2014-01-27 10:49:27.641 Playground[6566:3603] suscribe next (
    "http://66.55.93.205:8080/"
)
2014-01-27 10:50:27.161 Playground[6566:4103] suscribe error Error Domain=NSURLErrorDomain Code=-1001 "The request timed out." UserInfo=0x8b6efe0 {NSErrorFailingURLStringKey=http://valekalter.serverroom.us:9264/listen.pls, NSErrorFailingURLKey=http://valekalter.serverroom.us:9264/listen.pls, NSLocalizedDescription=The request timed out., NSUnderlyingError=0x8b6e520 "The request timed out."}

我希望subscribeNext/Error块被通知集合中的所有条目,以便我可以将条目标记为有效或无效.

如何使用活性可可来实现它.

UPDATE

我试过用下面的catch块替换订阅块.它只捕获第一个错误事件.

- (RACSignal *)processStationList
{
    NSArray *urlList = @[@"http://66.55.93.205/listen.pls",@"http://84.20.77.50:8000/listen.pls",@"http://valekalter.serverroom.us:9264/listen.pls", @"http://66.55.93.205:8080/listen.pls"];

    return [RACSignal createSignal:^RACDisposable *(id subscriber) {
        [[[urlList.rac_sequence.signal flattenMap:^RACStream *(NSString *urlString) {
            NSLog(@"flatten map %@",urlString);
            return [self fetchStationURLListForStation:urlString];
        }] catch:^RACSignal *(NSError *error) {
            NSLog(@"catch %@",error);
            return [RACSignal empty];
        }] subscribeNext:^(id x) {
            NSLog(@"subscribe next %@",x);
        }];
        return nil;
    }];
}

输出:

2014-01-27 10:55:45.801 Playground[6648:1303] flatten map http://66.55.93.205/listen.pls
2014-01-27 10:55:45.806 Playground[6648:1303] flatten map http://84.20.77.50:8000/listen.pls
2014-01-27 10:55:45.814 Playground[6648:1303] flatten map http://valekalter.serverroom.us:9264/listen.pls
2014-01-27 10:55:45.814 Playground[6648:1303] flatten map http://66.55.93.205:8080/listen.pls
2014-01-27 10:55:46.401 Playground[6648:3603] subscribe next (
    "http://66.55.93.205:8080/"
)
2014-01-27 10:55:46.402 Playground[6648:3603] subscribe next (
    "http://66.55.93.205:80/"
)
2014-01-27 10:55:57.728 Playground[6648:5007] catch Error Domain=NSURLErrorDomain Code=-1004 "Could not connect to the server." UserInfo=0x8b61730 {NSErrorFailingURLStringKey=http://valekalter.serverroom.us:9264/listen.pls, NSErrorFailingURLKey=http://valekalter.serverroom.us:9264/listen.pls, NSLocalizedDescription=Could not connect to the server., NSUnderlyingError=0x8b60f70 "Could not connect to the server."}

如何捕捉所有错误？