观察RACSequence中的每一项 [英] Observe every item in RACSequence

问题描述

我在 ParentViewModel 上有一个方法，它返回 ViewModel 对象的 RACSequence，如下所示:

I have a method on ParentViewModel which returns an RACSequence of ViewModel objects like so:

- (RACSequence *) viewModels
{
    return [self.models.rac_sequence map:^id(Model *model) {
        return [[ViewModel alloc] initWithModel: model];
    }];
}

每个 ViewModel 都有一个 state 属性，该属性是一个枚举并具有 3 个状态:NotStarted、InProgress 和 Completed.当我序列中的所有 ViewModel 都具有 Completed 状态时，我知道 ParentViewModel 是有效的.我在 ParentViewModel 上有一个 validSignal，我想从 viewModels 序列中推导出有效的事实.目前我有这个代码:

Each of the ViewModels has a state property on which is an enum and has 3 states: NotStarted, InProgress and Completed. When all the ViewModels in my sequence have the state Completed I know ParentViewModel is valid. I have a validSignal on the ParentViewModel which I want to derive the fact that is valid from the viewModels sequence. At the moment I have this code:

BOOL valid = [[self viewModels] all:^BOOL(ViewModel *vm) {
        return vm.state == Completed;
    }];

如果序列中的所有 ViewModel 都有效，它会给我一个指示.然后，我如何将其转换为 RACSignal，每当其中一个 ViewModel 上的 state 属性发生更改时，该 RACSignal 都会更新?

Which gives me an indicator if all ViewModels in the sequence are valid. How can I then turn this into a RACSignal which will update every time the state property on one of the ViewModels changes?

推荐答案

您首先需要将 state 转换为 RACSignal，然后一切就变得简单了.

You need first to turn state into a RACSignal, and then everything is easy from that point.

最终代码如下:

RACSignal *valid = [[RACSignal combineLatest:
                     [[self viewModels] map:^id(ViewModel *viewModel) {
                       return RACAbleWithStart(viewModel, state);
                     }]
                    ]
                    map:^(RACTuple *states) {
                      return @([states.rac_sequence all:^BOOL(NSNumber *state) {
                        return state.unsignedIntegerValue == Completed;
                      }]);
                    }
                   ];

第一个块将您的每个视图模型映射到一个信号，该信号观察 state 属性(将起始值作为信号的第一个值).

The first block maps each of your view models into a signal that observes the state property (with the starting value as first value of the signal).

combineLatest: 将采用 RACSignals 的集合，并创建一个新信号，每当其中一个底层信号发生变化时都会触发该信号，并发送一个 RACTuple 与每个信号的值.

combineLatest: will take a collection of RACSignals and will create a new signal that fires everytime one of the underlaying signals changes, and sends a RACTuple with the value of each signal.

那个RACTuple然后被转换成一个RACSequence，我们可以生成一个@YES或@NO的值code> 取决于所有值是否Completed.

That RACTuple is then converted into a RACSequence, and we can generate a value of @YES or @NO depending if all the values are Completed or not.

我认为结果就是您正在寻找的信号.

I think the result is the signal you were looking for.

(免责声明:我是 ReactiveCocoa 的新手，所以可能有更简单的方法).

(Disclaimer: I’m new to ReactiveCocoa, so there may be an easier way).

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