根据Dart / Flutter中的过滤器更新流 [英] Update streams based on filters in Dart/Flutter

问题描述

我有一个BLoC，它消耗原始输入 Stream （产生JSON对象列表），并使用 StreamTransformer将其转换为可用对象。 UI将显示该列表。用户可以应用过滤器（本身就是流到BLoC中的流），以便BLoC用相应的 where（...）语句更新输入流转换器。

I have a BLoC that consumes a raw input Stream (that yields a list of JSON objects) and transforms it to usable objects using a StreamTransformer. The UI shows that list. The user can apply a filter (itself a stream into the BLoC), such that the BLoC updates the input stream transformer with respective where(...) statements.

问题是：当过滤器更改时，UI不会更新，因为输出流取决于JSON输入流的事件，而不是过滤器流。我的假设是我需要创建自己的流，将输入事件和过滤器事件都转发到该流中，或者我需要在转换后的输入流上重复最后一个事件，以便转换器有机会将其拾取。如何正确完成？一个例子会很有帮助！

The question is: When the filter changes, the UI is not updated because the output stream depends on events of the JSON input stream, not the filter stream. My assumption is I need to either create my own stream into which I forward both input events and filter events, or I need to repeat on the transformed input stream the last event, such that the transformer has a chance to pick it up. How is this done properly? An example would help a lot!

推荐答案

您的假设是正确的。您需要创建第三个流，同时接收JSON流和Filter流，并将两者组合成自定义结果。

Your assumption is correct. You need to create a third steam that takes both your JSON and Filter streams and combine both into a custom result.

通常这是通过Stream转换器完成的。使用 myStream.transform 方法。但这有点复杂。

This is usually done with a Stream transformer. Using myStream.transform method. But this is kinda complicated.

为了使事情变得更加简单，有一个名为 rxdart 基本上是 Stream 的子类，并添加了一些常见的转换器。

To make things far easier, there's a package called rxdart which basically subclass Stream and adds a few common transformers.

使用rxdart，您可以使用 combineLatest 运算符

Using rxdart, you could create this third stream by using combineLatest operator

Observable<List<String>> list;
Observable<String> filter;

final output = Observable.combineLatest2(filter, list, (String filter, List<String> list) {
  return list.where((str) => str.startsWith(filter));
});

更多有关reactx运算符的信息此处

More informations on reactivex operators here

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