Kotlin 创建一个 class 的实例并在一行代码中实现回调

Question

我是 Kotlin 的新手，我已经设法修改了我的 Java 计时器 class 以便我可以用两行代码实现它。

请问有没有办法修改一下，一行代码实现？感谢您的任何建议。

两行实现：

fun testTimer() {
    var tmr = MyTimer(1000, true)
    tmr.onTimer = { doSometing() }
}

计时器class

class MyTimer {
    private var running = false
    private var repeatDelayMS: Int = 0
    private val handler = Handler()
    var onTimer:()-> Unit = {}

    private val runnable = object : Runnable {
        override fun run() {
            if (running) {
                onTimer()
                if (repeatDelayMS > 0)
                    handler.postDelayed(this, repeatDelayMS.toLong())
                else
                    stop()
            }
        }
    }

    constructor(repeatDelayMS: Int, runOnCreate: Boolean) {
        this.repeatDelayMS = repeatDelayMS
        if (runOnCreate)
            start()
    }

    fun start() {
        running = true
        handler.postDelayed(runnable, repeatDelayMS.toLong())
    }


    fun stop() {
        running = false
        handler.removeCallbacks(runnable)
    }
}

Answer 1

鉴于您的接口，您可能可以将属性声明移至主构造函数，并将 start() 移至 init 块。

另请注意 val 超过 var 会得到 immutable/read-only properties

// this is not one line now, but just for formatting purposes ;)
fun testTimer() {
    val timer = MyTimer(
            repeatDelayMS = 1000,
            runOnCreate = true,
            onTimer = { doSomething() }
    )
}

class MyTimer(
        private var running: Boolean = false,
        private val runOnCreate: Boolean,
        private val repeatDelayMS: Int = 0,
        private val handler: Handler = Handler(),
        private val onTimer: () -> Unit = {}
) {

    init {
        if (runOnCreate) {
            start()
        }
    }

    // the rest is the same
}

Answer 2

你可以

val tmr = MyTimer(1000, true).apply {
    onTimer = { doSomething() }
}

Kotlin 创建一个 class 的实例并在一行代码中实现回调

Kotlin make an instance of a class and implement a callback in one line of code

lambda

callback

kotlin

simplify