从ViewModel观察LiveData [英] Observing LiveData from ViewModel

问题描述

我有一个单独的类，负责处理数据提取(特别是Firebase)，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，但是问题是，为了获取所述值，我需要观察从数据获取类返回的LiveData对象.观察方法要求将LifecycleOwner对象作为第一个参数，但是我显然不在ViewModel中拥有该对象，并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

在此博客文章，在这种情况下，建议使用转换(请参见存储库中的LiveData"段落)，因为不应保留 ViewModel 与View相关的任何引用(活动，上下文等)，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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