从 ViewModel 观察 LiveData [英] Observing LiveData from ViewModel

问题描述

我有一个单独的类，我在其中处理数据获取(特别是 Firebase)，我通常从中返回 LiveData 对象并异步更新它们.现在我想将返回的数据存储在 ViewModel 中，但问题是为了获得所述值，我需要观察从我的数据获取类返回的 LiveData 对象.observe 方法需要 LifecycleOwner 对象作为第一个参数，但我的 ViewModel 中显然没有这个对象，而且我知道我不应该在 ViewModel 中保留对 Activity/Fragment 的引用.我该怎么办?

I have a separate class in which I handle data fetching (specifically Firebase) and I usually return LiveData objects from it and update them asynchronously. Now I want to have the returned data stored in a ViewModel, but the problem is that in order to get said value, I need to observe the LiveData object returned from my data fetching class. The observe method required a LifecycleOwner object as the first parameter, but I obviously don't have that inside of my ViewModel and I know I am not supposed to keep a reference to the Activity/Fragment inside of the ViewModel. What should I do?

推荐答案

在 这篇博文 由 Google 开发人员 Jose Alcérreca 撰写，建议在这种情况下使用转换(请参阅存储库中的 LiveData"段落)，因为 ViewModel 不应包含任何与 View(活动、上下文等)相关的参考，因为它很难测试.

In this blog post by Google developer Jose Alcérreca it is recommended to use a transformation in this case (see the "LiveData in repositories" paragraph) because ViewModel shouldn't hold any reference related to View (Activity, Context etc) because it made it hard to test.

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