android-Kotlin：不可变类型对可变类型内部变量的只读访问

在Android中学习ViewModels时,出现了一个问题,感觉像是要解决Kotlin.在下面的代码中,我们可以看到MutableLiveData值正在用于编辑值和指标.但是,我们不希望这些可变值暴露给其他任何事物,特别是Android生命周期的成员.我们确实希望Android Lifecycle成员有权读取值,但不能设置它们.因此,下面显示的3个公开功能是LiveData的功能.不变类型.

有没有更简单或更简洁的方法来公开可以在内部编辑的只读值？这似乎是Kotlin要避免的事情：样板冗长.

class HomeListViewModel: ViewModel(){
    //Private mutable data
    private val repositories = MutableLiveData<List<Repo>>()
    private val repoLoadError = MutableLiveData<Boolean>()
    private val loading = MutableLiveData<Boolean>()


    //Exposed uneditable LIveData
    fun getRepositories():LiveData<List<Repo>> = repositories
    fun getLoadError(): LiveData<Boolean> = repoLoadError
    fun getLoadingStatuses(): LiveData<Boolean> = loading

    init{...//Do some stuff to MutableLiveData<>

    }
}

可能类似的非Android场景是：

class ImmutableAccessExample{

    private val theThingToBeEditedInternally = mutableListOf<String>()

    fun theThingToBeAccessedPublicly(): List<String> = theThingToBeEditedInternally

    init {
        theThingToBeEditedInternally.add(0, "something")
    }

}

解决方法:

我不知道是否有可能避免冗长.但是,我之前已经看到过,通常将其声明为属性.

private val _repositories = MutableLiveData<List<Repo>>()
val repositories : LiveData<List<Repo>> 
    get() = _repositories

这是约定,请参阅名称中的the doc here作为后备属性

If a class has two properties which are conceptually the same but one is part of a public API and another is an implementation detail, use an underscore as the prefix for the name of the private property:

标签：kotlin,android-viewmodel,android
来源： https://codeday.me/bug/20191110/2013459.html