Writing a timer using Handler in Kotlin

Question

I'm trying to implement an Android timer in Kotlin which will fire an event at a defined time interval. I dont want to use TimerTask due to its documented weaknesses (see here) and although there are potentially other ways to do it, I'd like to use a Handler/Runnable in a post-delayed loop. In Java this is possible since the Runnable can refer to itself in the initializer, however in Kotlin it seems this is not possible:

private fun startBoutiqueRefreshTimer(delayMs: Long) {
    val handler = Handler()
    val runnable = Runnable() {
        EventManager.post(BoutiqueRefreshTimerEvent())
        handler.postDelayed(runnable, delayMs)
    }
    handler.postDelayed(runnable, delayMs)
}

because runnable cannot be resolved in the inner postDelayed call. Kotlin apparently prevents variable references from within their own initializers.

What would be a good solution to this problem, still using the Handler/Runnable approach?

Answer 1

This will work

val updateHandler = Handler()

    val runnable = Runnable {
        updateDisplay() // some action(s)
    }

    updateHandler.postDelayed(runnable, 5000).

private fun updateDisplay() {
      Do actions
}

Or if you are not too much familiar with Kotlin, write your code and convert your android Code to Kotlin using Ctrl+Alt+Shift+K".

Answer 2

You could also use something like this:

private fun startBoutiqueRefreshTimer(delayMs: Long) {
    Handler().apply {
        val runnable = object : Runnable {
            override fun run() {
                EventManager.post(BoutiqueRefreshTimerEvent())
                postDelayed(this, delayMs)
            }
        }
        postDelayed(runnable, delayMs)
    }
}

I used here apply() function to simplify Handler variable, and object expression to allow referencing to Runnable.

As you can see, when I used object expression to initialize Runnable (instead of lambda), then I can use this to reference to Runnable object.

Answer 3

You could move the routine you want to execute periodically in a separate function:

val runnable = Runnable { doJob() }

fun doJob() {
    EventManager.post(BoutiqueRefreshTimerEvent())
    handler.postDelayed(runnable, delayMs)
}

Note that the variable runnable needs to be accessable in scope of the doJob()-function, that means it should be a class-member, if you are in a class/object.