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在 Android 的 MVVM 中将 ViewModel State 保存在哪里？

[英]Where to Save ViewModel State in Android's MVVM?

原文 2020-12-20 05:09:51 6 1 java/ android/ kotlin/ mvvm/ viewmodel

As a beginner to Android development, I am trying to clean up my codebase from my first app by converting it to the recommended MVVM structure.作为 Android 开发的初学者，我正在尝试通过将我的第一个应用程序转换为推荐的 MVVM 结构来清理我的代码库。 What I am currently stuck on, is trying to figure out the best way to store my view model's state.我目前坚持的是试图找出存储我的视图模型 state 的最佳方法。

In this example, the state I need to store is simply an ArrayList of strings (indicating which checkboxes in a recyclerview are checked).在这个例子中，我需要存储的 state 只是一个 ArrayList 字符串（表示选中了回收视图中的哪些复选框）。 I am currently storing this ArrayList inside of my ViewModel as a field, wrapped inside of a MutableLivedata object, which my activity observes.我目前将这个 ArrayList 作为一个字段存储在我的 ViewModel 中，包裹在我的活动观察到的 MutableLivedata object 中。 This method of storing the ViewModel state as a field does not seem viable in the long run.从长远来看，这种将 ViewModel state 存储为字段的方法似乎不可行。 I can imagine as my app grows my ViewModel classes would get quite bloated and messy.我可以想象随着我的应用程序的增长，我的 ViewModel 类会变得非常臃肿和混乱。

I currently use a Firebase Realtime Database to store my data that I need persisted, accessed through a repository just as Android Architecture recommends.我目前使用 Firebase 实时数据库来存储我需要持久化的数据，就像 Android 架构建议的那样，通过存储库访问。 My ViewModel's state, however, does not need to be persisted after the app closes, so it would definitely not make sense to make network calls to my Firebase Database for it.然而，我的 ViewModel 的 state 不需要在应用程序关闭后持久化，因此对我的 Firebase 数据库进行网络调用绝对没有意义。

My question is: Where would make the most sense to save my ViewModel's state?我的问题是：在哪里保存 ViewModel 的 state 最有意义？ The semi-sensible options I see in front of me are saving it as fields in my ViewModel class (my current approach), saving it in a Room database (and resetting the database each time the app is killed), or saving it as fields in my repository class (doesn't seem right).我在我面前看到的半明智选项是将其保存为 ViewModel class 中的字段（我当前的方法），将其保存在 Room 数据库中（并在每次应用程序被终止时重置数据库），或将其保存为字段在我的存储库 class 中（似乎不对）。 I'm open to suggestions!我愿意接受建议！

1 个解决方案

It depends on your needs:这取决于您的需求：

If you want to keep state just for configuration changes, you do not need to do anything more.如果您只想保留 state 以进行配置更改，则无需再进行任何操作。 ViewModel will handle it for you. ViewModel 将为您处理它。
If you want to see the same state when you come back to that screen after closing it, then I would recommend to use a local cache solution such as Room.如果您想在关闭屏幕后返回该屏幕时看到相同的 state，那么我建议您使用本地缓存解决方案，例如 Room。 You can create a repository on top of room and inject it into your Viewmodel.您可以在房间顶部创建一个存储库并将其注入您的 Viewmodel。
If you want to keep state until application closes, you can also create an in-memory repository (a singleton repo with the state).如果您想在应用程序关闭之前保留 state，您还可以创建一个内存存储库（带有状态的 singleton 存储库）。 When application is killed that memory will be reclaimed by the OS so that they will be cleared.当应用程序被杀死时，操作系统将回收 memory 以便清除它们。

In any case storing data remotely does not seem to be the the solution that you are looking for.在任何情况下，远程存储数据似乎都不是您正在寻找的解决方案。

I would also not rely on memory cache solution because of Android system memory reclaim situations.我也不会依赖 memory 缓存解决方案，因为 Android 系统 memory 回收情况。

You can go with the cache solution and clear your cache when you open the app again.您可以使用缓存解决方案 go 并在再次打开应用程序时清除缓存。