Android Weekly Notes #427

2020-08-23 本文已影响0人圣骑士wind

Android Weekly Issue #427

Composite ViewModel

添加需求会让ViewModel变得越来越庞大, 所以需要拆分ViewModel.

具体做法是抽取了delegates. 每个delegate是一个mini的ViewModel.

作者还有例子.

作者的例子用了这个状态管理的库: https://github.com/beworker/knot/

首先声明Delegate的接口:

interface Delegate {
    fun CompositeKnot<State>.register()
    fun CompositeKnot<State>.onEvent(event: Event): Boolean
}

然后从构造传入ViewModel:

class CompositeBooksViewModel(
    private val delegates: List<Delegate>
) : BooksViewModel()

初始化:

init {
    for (delegate in delegates) {
        with(delegate) { knot.register() }            
    }
    knot.compose()
}

实际的逻辑处理就被放在了代理中:

class ClearButtonDelegate : Delegate {
    override fun CompositeKnot<State>.register() {
        registerDelegate<Change, Nothing> {
            changes {
                reduce<Change.Clear> { change ->
                    when (this) {
                        is State.Content -> State.Empty.only
                        is State.Empty -> only
                        else -> unexpected(change)
                    }
                }
            }
        }
    }
}