android - 如何从 KClass 反射进行 Kotlin 类型推断？

Question

在下面的代码中，我无法正确安排输入/输出以使 from() 和 to() 都按预期工作。我试过在属性和函数参数中切换进/出，但总是以不正确的输入错误告终。

class KStateMachine(private val states: List<StateHandler>) {

var currentState: KClass<out StateHandler>
    private set
private val handlers:HashMap<KClass<in StateHandler>, Int> = HashMap()

init {
    currentState = states[0]::class

    for (i in 0..states.size - 1) {
        handlers.put(states[i]::class, i)
    }
}

fun goto(toState: KClass<in StateHandler>) {
    var index = handlers.get(toState)
    if (index != null) {
        var oldState = currentState
        currentState = toState
        states.get(index).from(oldState)
    } else {
        throw RuntimeException("to state unknown")
    }
}

inline fun <reified T: StateHandler> goto() {
    goto(T::class)
}

abstract class StateHandler {
    abstract fun from(fromState: KClass<in StateHandler>)
}
}

Answer 1

我想您根本不需要in-KClasses 的投影:您的代码似乎没有传递StateHandler 或用 StateHandler 参数化到 KClass 的函数中。

如果变体的目的是您希望所有的 KClass 代表 StateHandler 的子类型，那么您可以使用 out -无处不在的投影:

class KStateMachine(private val states: List<StateHandler>) {

    private var currentState: KClass<out StateHandler>
    private val handlers: HashMap<KClass<out StateHandler>, Int> = HashMap()

    init {
        currentState = states[0]::class

        for (i in 0..states.size - 1) {
            handlers.put(states[i]::class, i)
        }
    }

    fun to(toState: KClass<out StateHandler>) {
        var index = handlers.get(toState)
        if (index != null) {
            var oldState = currentState
            currentState = toState
            states.get(index).from(oldState)
        } else {
            throw RuntimeException("to state unknown")
        }
    }

    abstract class StateHandler {
        abstract fun from(fromState: KClass<out StateHandler>)
    }
}