创建一个元素比原始元素更多的 ReactiveUI 派生集合 [英] Creating a ReactiveUI derived collection with more elements than the original

问题描述

是否可以创建一个包含比原始元素更多的 ReactiveUI 派生集合?

Is it possible to create a ReactiveUI derived collection that has more elements in it than the original?

我已经看到有一种过滤集合和选择单个属性的方法，但我正在寻找的是等效于可枚举的 SelectMany 操作.

I've seen that there is a way of filtering a collection, and selecting single properties, but what I'm looking for is the equivalent of the SelectMany operation for enumerables.

举个例子，想象一下试图获得一个派生集合，代表每一个陷入交通拥堵的乘客.

To illustrate, imagine trying to get a derived collection representing every passenger stuck in a traffic jam.

class Car 
{
    ReactiveCollection<Passenger> Passengers;
}

var TrafficJam=new ReactiveCollection<Car>();
EveryPassengerInTheTrafficJam=Cars.CreateDerivedCollection(c=>c.Passengers);

以上不起作用，我认为错误是 IEnumerable> can't be cast to ReactiveCollection - 或者其他什么在任何情况下，都要处理类型.

The above doesn't work, I think the error was IEnumerable<ReactiveCollection<Passenger>> can't be cast to ReactiveCollection<Passenger> - or something up with the types, in any case.

我无法找出这种扁平化的正确方法 - 诚然，我在这里可能完全错误的树，所以请告诉我是否有更好的方法来实现同样的目标！

I can't figure out the right approach for this flattening - admittedly I may be barking up completely the wrong tree here, so please let me know if there's a better way of achieving the same thing!

推荐答案

目前，CreateDerivedCollection 不支持 SelectMany 作为转换，这太棘手了手柄移除.如果你没有很多项目，你可以每次都重新生成集合:

At the moment, CreateDerivedCollection doesn't support SelectMany as a transformation, it gets too Tricky to handle removes. If you don't have many items, you can just regenerate the collection every time:

cars.Changed
    .Select(_ => cars.SelectMany(x => x.Passengers).ToList())
    .ToProperty(this, x => x.Passengers);

好的，我们开始:

var whenCarsOrPassengersInThoseCarsChange = Observable.Merge(
    cars.Changed
        .SelectMany(_ =>
            cars.Select(x => x.Passengers.Changed).Merge())
        .Select(_ => Unit.Default),
    cars.Changed.Select(_ => Unit.Default));

whenCarsOrPassengersInThoseCarsChange.StartWith(Unit.Default)
    .Select(_ => cars.SelectMany(x => x.Passengers).ToList())
    .ToProperty(this, x => x.Passengers);

因此，我们的想法是，当我们想要重新评估乘客列表时，有两种主要情况:

So, the idea is that we've got two main situations when we want to reevaluate the passengers list:

1. 当其中一名乘客换车时
2. 当其中一辆车发生变化时

然而，棘手的部分是，我们只想观察集合中汽车的乘客(即，如果汽车被移除，我们不再关心它的乘客).

However, the tricky part is, we only want to watch passengers for cars in the collection (i.e. if a car is removed, we no longer care about its passengers).

所以，那个奇怪的 SelectMany 中的想法是，每次汽车列表发生变化时，构建一个新的 Observable 列表来表示乘客集合何时发生变化，并将它们合并在一起".

So, the idea in that weird SelectMany is, "Every time the car list changes, build a new list of Observables that represent when the passenger collection changes, and merge them all together".

但是，如果我们只有有那个声明，我们将不得不等待添加一辆车并且它的乘客改变，然后我们才能获得新的乘客名单，所以当汽车列表也发生变化时，我们也必须更新.

However, if we only had that statement, we would have to wait for a car to be added and its passengers change before we got a new passenger list, so we also have to update when the list of cars change too.

在这种情况下，我实际上并不关心这些 Observable 输出的值，只是当它们发生时.Unit"是 void 的 Rx 版本，它只有一个值，Unit.Default".当你只关心事情发生的时候，你会使用它，而不是它的价值是什么.

In this case, I actually don't care about the values that these Observables put out, just when they happen. "Unit" is the Rx version of void, it only has a single value, "Unit.Default". You use it when you only care when something happens, not what the value of it is.

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