如何有条件地缓冲RACSignal值？

Question

我正在研究一些通过websockets与远程API交互的代码.我的数据层负责建立和监控websocket连接.它还包含应用程序可用于排队要发送的websocket消息的方法.应用程序代码不应该负责检查websocket连接的状态,即"即发即忘".

理想情况下,我希望数据层的功能如下:

• 当数据层没有与websocket endpoint(self.isConnected == NO)的连接时,消息在内部缓冲.
• 当连接变为可用(self.isConnected == YES)时,立即发送缓冲的消息,并立即发送任何后续消息.

这是我能够提出的:

#import "RACSignal+Buffering.h"

@implementation RACSignal (Buffering)

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

        RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable];

        NSMutableArray* bufferedValues = [[NSMutableArray alloc] init];
        __block BOOL buffering = NO;

        void (^bufferHandler)() = ^{
            if (!buffering)
            {
                for (id val in bufferedValues)
                {
                    [subscriber sendNext:val];
                }

                [bufferedValues removeAllObjects];
            }
        };

        RACDisposable* bufferDisposable = [shouldBuffer subscribeNext:^(NSNumber* shouldBuffer) {

            buffering = shouldBuffer.boolValue;
            bufferHandler();

        }];

        if (bufferDisposable)
        {
            [disposable addDisposable:bufferDisposable];
        }

        RACDisposable* valueDisposable = [self subscribeNext:^(id x) {

            [bufferedValues addObject:x];
            bufferHandler();

        } error:^(NSError *error) {
            [subscriber sendError:error];
        } completed:^{
            [subscriber sendCompleted];
        }];

        if (valueDisposable)
        {
            [disposable addDisposable:valueDisposable];
        }

        return disposable;
    }];
}

@end

最后,这是如何使用它的伪代码:

@interface APIManager ()

@property (nonatomic) RACSubject* requests;

@end

@implementation WebsocketDataLayer

- (id)init
{
    self = [super init];

    if (self) {

        RACSignal* connectedSignal = RACObserve(self, connected);

        self.requests = [[RACSubject alloc] init];

        RACSignal* bufferedApiRequests = [self.requests bufferWithSignal:connectedSignal];

        [self rac_liftSelector:@selector(sendRequest:) withSignalsFromArray:@[bufferedApiRequests]];
    }
    return self;
}

- (void)enqueueRequest:(NSString*)request
{
    [self.requests sendNext:request];
}

- (void)sendRequest:(NSString*)request
{
    DebugLog(@"Making websocket request: %@", request);
}

@end

我的问题是:这是缓冲价值的正确方法吗？是否有更惯用的RAC处理方式？

Answer 1

缓冲可以被认为是适用于单个请求的东西,这导致使用-flattenMap:和自然实现RACObserve:

@weakify(self);
RACSignal *bufferedRequests = [self.requests flattenMap:^(NSString *request) {
    @strongify(self);

    // Waits for self.connected to be YES, or checks that it already is,
    // then forwards the request.
    return [[[[RACObserve(self, connected)
        ignore:@NO]
        take:1]
        // Replace the property value with our request.
        mapReplace:request];
}];

如果订购很重要,您可以-flattenMap:使用-map:plus 替换-concat.这些实现避免了对任何自定义操作符的需要,并且无需手动订阅(这是众所周知的混乱).