在代码中，lambda的类型不匹配，它是如何工作的?

Question

我在Android上使用Epoxy library

我好奇的是为什么lambda expression的parameter在类型不匹配时不会得到错误。

listener是一个以Int type为参数的lambda expression。

但listener(addDetailClicked)工作正常

不应该是listener(Int)吗?或listener({ i -> addDetailClicked(i) }).

实际上，我不知道为什么在我写完代码后它还能工作。

这怎么可能?

@EpoxyModelClass(layout = R.layout.item_routine)
abstract class EpoxyRoutineModel() : EpoxyModelWithHolder<EpoxyRoutineModel.Holder>() {
@EpoxyAttribute
var workout: String = "see"
@EpoxyAttribute
var curPos: Int = 0
@EpoxyAttribute
lateinit var listener: (Int) -> Unit // this
override fun bind(holder: Holder) {
holder.workout.text = workout
holder.add_btn.setOnClickListener {
listener(curPos)
}
}
}

控制器

class RoutineItemController(
private val addDetailClicked: (Int) -> Unit)
: EpoxyController() {
private var routineItem : List<RoutineItem>? = emptyList()
override fun buildModels() {
var i:Int =0
routineItem?.forEach {
when(it) {
is RoutineItem.RoutineModel ->
EpoxyRoutineModel_()
.id(i++)
.curPos(i++)
.workout("d")
.listener(addDetailClicked) // why? listener(Int) or listener({ i -> addDetailClicked(i) })
.addTo(this)
}
}
}
}

class WriteRoutineFragment : Fragment() {
private var _binding : FragmentWriteRoutineBinding? = null
private val binding get() = _binding!!
private lateinit var epoxyController : RoutineItemController
private val vm : WriteRoutineViewModel by viewModels { WriteRoutineViewModelFactory() }
override fun onCreateView(inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?): View? {
_binding = FragmentWriteRoutineBinding.inflate(inflater, container, false)
epoxyController = RoutineItemController(::addDetail)
binding.rv.adapter = epoxyController.adapter
binding.rv.itemAnimator = null
return binding.root
}
private fun addDetail(pos: Int) {
vm.addDetail2(pos)
}
}

Answer 1

我相信您错过了EpoxyRoutineModel_包含EpoxyRoutineModel中发现的数据类型的设置器的事实。例如，EpoxyRoutineModel.curPos的类型是Int，因此EpoxyRoutineModel_.curPos()是一个声明为:

的函数:

fun curPos(Int): EpoxyRoutineModel_

(或相似的)同样，EpoxyRoutineModel.listener类型为(Int) -> Unit，因此EpoxyRoutineModel_.listener()声明为:

fun listener((Int) -> Unit): EpoxyRoutineModel_

所以listener()是一个接收另一个函数(它自己接收Int)的函数。所以我们可以在这里提供addDetailClicked。