如何在 android 应用程序中共享 LiveData 的实例? [英] How to share an instance of LiveData in android app?

问题描述

简单用例

我正在使用 MVVM 架构和 Android 架构组件 在我的应用中.

I am using MVVM architecture and Android Architecture Components in my app.

用户登录后，我正在获取多个网络数据并希望从不同的ViewModels 附加到不同的 Activity 生命周期.

After user logs in, I am fetching multiple network data and want to have access to it from different ViewModels attached to different Activities lifecycle.

我不想在我的应用中使用 Room Persistence Library.

I don't want to use Room Persistence Library in my app.

我看到了一些关于在 Activity 之间共享 ViewModel 或使用 LiveData 作为静态成员，但我认为大多数情况下我们需要在多个屏幕中访问相同的数据.

I have seen some question about sharing a ViewModel between Activities or using a LiveData as static member, but I think most of the cases we need to access the same data in multiple screens.

我想分享一个解决方案，但如果有更好的解决方案或有问题，请发表您的想法.

I want to share a solution, but if there is better one or there is an issue with this, please post your thoughts.

推荐答案

这个想法是有一个 Singleton 存储库，在使用者(ViewModels)之间共享一个LiveData.

The idea is to have a Singleton Repository, which shares a LiveData between consumers (ViewModels).

class SharedLiveDataRepository(val dataSource: MyDataSource) {

    // This LiveData is shared across consumers
    private val result = MutableLiveData<Long>()

    fun loadData(): LiveData<Long> {
        if (result.value == null) {
            result.value = dataSource.getData()
        }
        return result
    }

}

如果出于某种原因您想刷新数据，loadItem 方法可以如下所示

If for some reason you would like to refresh the data, the loadItem method can look like this

  fun loadData(refresh: Boolean = false): LiveData<Long> {
        if (refresh == true) {
            result.value = null
        } 
        if (result.value == null) {
            result.value = dataSource.getData()
        }
        return result
    }

请注意:刷新数据可能会出现故障.

Please Note: For refreshing the data it is possible to see a glitch.

想象一个场景，两个 Activity 之间有转换，第一个是观察 LiveData，第二个开始刷新它.

Imagine a scenario when there is transition between two activities and first one is observing the LiveData and the second one starting refreshing it.

我认为上述问题的解决方案是在第一个活动中进行刷新，然后导航到下一个活动.

I think the solution for the above issue is to do the refresh in first activity and then navigate to the next one.

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