How to call a function after delay in Kotlin?

Question

As the title, is there any way to call a function after delay (1 second for example) in Kotlin?

Answer 1

There is also an option to use Handler -> postDelayed

 Handler().postDelayed({
                    //doSomethingHere()
                }, 1000)

Answer 2

Many Ways

1. Using Handler class

Handler().postDelayed({
    TODO("Do something")
    }, 2000)

2. Using Timer class

Timer().schedule(object : TimerTask() {
    override fun run() {
        TODO("Do something")
    }
}, 2000)

// Shorter

Timer().schedule(timerTask {
    TODO("Do something")
}, 2000)


// Shortest

Timer().schedule(2000) {
    TODO("Do something")
}

3. Using Executors class

Executors.newSingleThreadScheduledExecutor().schedule({
    TODO("Do something")
}, 2, TimeUnit.SECONDS)

Answer 3

You can use Schedule

inline fun Timer.schedule(
    delay: Long, 
    crossinline action: TimerTask.() -> Unit
): TimerTask (source)

example (thanks @Nguyen Minh Binh - found it here: http://jamie.mccrindle.org/2013/02/exploring-kotlin-standard-library-part-3.html)

import java.util.Timer
import kotlin.concurrent.schedule

Timer("SettingUp", false).schedule(500) { 
   doSomething()
}

Answer 4

You could launch a coroutine, delay it and then call the function:

 /*GlobalScope.*/launch {
   delay(1000)
   yourFn()
 }

If you are outside of a class or object prepend GlobalScope to let the coroutine run there, otherwise it is recommended to implement the CoroutineScope in the surrounding class, which allows to cancel all coroutines associated to that scope if necessary.

Answer 5

You have to import the following two libraries:

import java.util.*
import kotlin.concurrent.schedule

and after that use it in this way:

Timer().schedule(10000){
    //do something
}

Answer 6

val timer = Timer()
timer.schedule(timerTask { nextScreen() }, 3000)

Answer 7

If you're using more recent Android APIs the Handler empty constructor has been deprecated and you should include a Looper. You can easily get one through Looper.getMainLooper().

    Handler(Looper.getMainLooper()).postDelayed({
        //Your code
    }, 2000) //millis

Answer 8

If you are in a fragment with viewModel scope you can use Kotlin coroutines:

    myViewModel.viewModelScope.launch {
        delay(2000)
        // DoSomething()
    }

Answer 9

A simple example to show a toast after 3 seconds :

fun onBtnClick() {
    val handler = Handler()
    handler.postDelayed({ showToast() }, 3000)
}

fun showToast(){
    Toast.makeText(context, "Its toast!", Toast.LENGTH_SHORT).show()
}

Answer 10

If you are looking for generic usage, here is my suggestion:

Create a class named as Run:

class Run {
    companion object {
        fun after(delay: Long, process: () -> Unit) {
            Handler().postDelayed({
                process()
            }, delay)
        }
    }
}

And use like this:

Run.after(1000, {
    // print something useful etc.
})

Answer 11

i suggest to use kotlin coroutine and if you want to cancel it. its simple and light weight.

fun repeatFun(): Job {
    return coroutineScope.launch {  
        while(isActive) {
            //do your work here
            delay(1000)
        }
    }
}

//start the loop
val repeatFun = repeatRequest()

//Cancel the loop
repeatFun.cancel()

Answer 12

I recommended using SingleThread because you do not have to kill it after using. Also, "stop()" method is deprecated in Kotlin language.

private fun mDoThisJob(){

    Executors.newSingleThreadScheduledExecutor().scheduleAtFixedRate({
        //TODO: You can write your periodical job here..!

    }, 1, 1, TimeUnit.SECONDS)
}

Moreover, you can use it for periodical job. It is very useful. If you would like to do job for each second, you can set because parameters of it:

Executors.newSingleThreadScheduledExecutor().scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit);

TimeUnit values are: NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS, MINUTES, HOURS, DAYS.

Answer 13

I use the following function(s):

fun <T> delayedAsyncTask(delayMs: Long = 0, task: () -> T): ScheduledFuture<T> {
    return Executors
        .newSingleThreadScheduledExecutor()
        .schedule(Callable<T> { task() }, delayMs, TimeUnit.MILLISECONDS)
}

fun <T> asyncTask(task: () -> T) = delayedAsyncTask(0, task)

Here's a unit test for the delayed function. Use of the returned future is optional of course.

    @Test
    fun `delayed task work correctly`() {
        val future = delayedAsyncTask(1000) {
            "lambda returns hello world"
        }
        assertEquals(false, future.isDone)
        Thread.sleep(1100)
        assertEquals(true, future.isDone)
        assertEquals("lambda returns hello world", future.get())
    }

Answer 14

Another way to create a redundant job other than this; that does not require the function to be suspend.

   val repeatableJob = CoroutineScope(Dispatchers.IO).launch {
        while (true) {
            delay(1000)
        }
    }

Cancel when you are done - repeatableJob.cancel()

Answer 15

if you are call function in UI.

Timer().schedule(1000) {
  activity?.runOnUiThread {
    doSomething()
  }
}