Android - Kotlin Handler cancel postDelayed task-CodePudding

I have the code that is attached below. The purpose is just to test canceling the scheduled task created with Handler. Inside the onCreate function I defined runnable, which I passed as an argument to both schedule and cancel function. My goal is to schedule the function, but cancel it before it comes to its execution. I am trying to cancel the scheduled task with removeCallbacks function. I also did try using function removeCallbacksAndMessages passing null as an argument, as well as passing Integer value as a token, which I passed as well inside the postDelay function. None of the mentioned did not cancelled the scheduled task function. Many thanks for any of your help.

class MyFragment: Fragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val runnable = Runnable {
            task()
        }
        this.schedule(runnable)
        this.cancelSchedule(runnable)
    }

    fun schedule(runable: Runnable) {
        Log.d("Schedule", "schedule")
        Handler(Looper.getMainLooper()).postDelayed(runable, 5000)
    }

    fun cancelSchedule(runable: Runnable) {
        Log.d("Cancel", "cancele")
        Handler(Looper.getMainLooper()).removeCallbacksAndMessages(runable)
    }

    fun task(){
        Log.d("TASK", "run")
    }
}

CodePudding user response：

Every Handler instance has its own message queue. Since you keep creating new Handlers in both your schedule and cancelSchedule functions, you are not working with the same queue.

You need a single Handler instance to be able to do this, so you should store it in a property.

class MyFragment: Fragment() {
    private val handler = Handler(Looper.getMainLooper())

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val runnable = Runnable {
            task()
        }
        this.schedule(runnable)
        this.cancelSchedule(runnable)
    }

    fun schedule(runable: Runnable) {
        Log.d("Schedule", "schedule")
        handler.postDelayed(runable, 5000)
    }

    fun cancelSchedule(runable: Runnable) {
        Log.d("Cancel", "cancele")
        handler.removeCallbacksAndMessages(runable)
    }

    fun task(){
        Log.d("TASK", "run")
    }
}