Kotlin 类属性不变

Question

我想要一个 kotlin 类来管理一些练习的当前目标。为此有两个主要函数，updateTarget()，它转到列表中的下一个目标，currentTarget()，它只是返回当前目标。

但是，目标从未真正改变过。 x 始终为 0。

我对此有两个问题。首先，为什么属性没有变化？其次，我是否缺少另一种更适合我的目标的设计模式？

class Targets(private val targets: ArrayList<Target>)
{
    init {
        require(targets.size > 1) {"There must be more than one target in targets"}
    }

    // Keeps track of current index of target. Has a range of 0 to targets.size-1
    private var x = 0

    /**
     * Returns the current exercise target
     */
    fun currentTarget() : Target {
        return targets[x]
    }

    /**
     * Updates the current exercise target to the next target in the list
     *
     * Returns true if a repetition has been made.
     */
    fun updateTarget() : Boolean {
        x += 1
        x %= targets.size
        return x == 0
    }
}

代码调用者：

if (target.isMetBy(value)) {
    val repetitionMade = currentExercise.targets.updateTarget()
    target = currentExercise.targets.currentTarget()
    if (repetitionMade) {
        numberRepetitions += 1
    }
}

实际上，目标永远不会改变，即使价值达到了目标。

Answer 1

对我来说，您的代码运行良好。 （Java 11 AdoptOpenJDK 上的 Kotlin 1.3.50）

这样运行：

class TargetApp {}
fun main() {
    val targets = Targets(arrayListOf(Target("one"), Target("two"), Target("three")))

    var numberRepetitions = 0;
    for(i in 1..10){
        val current = targets.currentTarget()
        val repetitionMade = targets.updateTarget()
        if(repetitionMade){
            numberRepetitions += 1
        }
        println("Index $i with current target '${current.name}' and $numberRepetitions repetitions")
    }
}

与目标

data class Target(
    val name: String
)

和“目标”

class Targets(private val targets: ArrayList<Target>) {
    init {
        require(targets.size > 1) { "There must be more than one target in targets" }
    }

    private var x = 0

    fun currentTarget(): Target {
        return targets[x]
    }

    fun updateTarget(): Boolean {
        x += 1
        x %= targets.size
        return x == 0
    }
}

输出：

Index 1 with current target 'one' and 0 repetitions
Index 2 with current target 'two' and 0 repetitions
Index 3 with current target 'three' and 1 repetitions
Index 4 with current target 'one' and 1 repetitions
Index 5 with current target 'two' and 1 repetitions
Index 6 with current target 'three' and 2 repetitions
Index 7 with current target 'one' and 2 repetitions
Index 8 with current target 'two' and 2 repetitions
Index 9 with current target 'three' and 3 repetitions
Index 10 with current target 'one' and 3 repetitions

我猜你的问题出在其他地方。

（我交换了 currentTarget 和 updateTarget 的调用，否则你的第一个“当前”目标将来自索引 1，因此跳过索引 0。）