Handler post is not working in Kotlin Android

Question

Could someone show me what is wrong?

I try to use a Handler post a Runnable but it's not execute

var mHandler: Handler? = null

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    mHandler = Handler()
    var runnable = Runnable {
        Log.d("TEST", "++++ runable")
        Log.d("TEST", "++++ come end")
    }
    Log.d("TEST", "++++ runnable" + runnable)
    Log.d("TEST", "++++ handle" + mHandler)
    mHandler!!.post { runnable }
}

This is output

09-21 00:56:04.067 4419-4419/? D/TEST: ++++ runnablecom.vpioneer.activity.MainActivity$onCreate$runnable$1@529b8fb4 09-21 00:56:04.067 4419-4419/? D/TEST: ++++ handleHandler (android.os.Handler) {529b8cb4}

I would recommend changing your first line to `lateinit var mHandler: Handler` since you are creating it `onCreate`. Then you don't need to worry about the nullability concerns. — Ruckus T-Boom, Sep 21 '17 at 14:38

score 22 · Accepted Answer · edited Sep 21 '17 at 08:48

22

First at all, don't use !! operator, it is a very bad practice (from the doc). With ? you will reach the same behaviour but checking if the instance became null before executing it.

Saying this, using:

mHandler?.post { runnable }

You are actually creating a new lambda containing runnable line. see here below in a more readable way:

mHandler?.post { 
   runnable 
}

This is the equivalent in Java:

mHandler.post(new Runnable(){
    public void run(){
        runnable;
    }
});

To solve this:

Option 1: getting rid of the runnable declaration

mHandler?.post { /*the content of your runnable*/ }

Option 2: using your runnable instance

mHandler?.post(runnable) // normal parentheses

Option 3: crazy way

mHandler?.post { runnable.run() }

edited Sep 21 '17 at 08:48

Willi Mentzel

27,862
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answered Sep 21 '17 at 08:34

crgarridos

8,758
3
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Thank you very much, My big mistake – songoku1610 Sep 21 '17 at 08:39
I made the same mistake. Thank you sir for pointing that out. – Mauker May 24 '18 at 04:10
!! is not necessarily bad practice if something absolutely shouldn't be null. Otherwise problem might be masked. On the other hand ?. will suffice and be preferred for most situations. – JohnyTex Feb 01 '22 at 11:59

score 3 · Answer 2 · answered Apr 17 '18 at 08:31

3

Try this code, I hope this is working

   Handler().postDelayed({
            // You code and delay time
   }, 1000L)

answered Apr 17 '18 at 08:31

Najib.Nj

3,706
1
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1

Thx @NajibAhmedPuthawala , Upvoted for saving my day – Ravi Vaniya May 01 '19 at 12:12

score 1 · Answer 3 · answered Sep 21 '17 at 08:26

1

You are not starting runnbale. Try this:

mHandler!!.post { runnable.run() }

This is also valid:

mHandler!!.post { 
    Log.d("TEST", "++++ runable")
    Log.d("TEST", "++++ come end")
}

answered Sep 21 '17 at 08:26

Aleksander Mielczarek

2,787
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I get an error: **java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()** – IgorGanapolsky Dec 06 '17 at 19:06

Handler post is not working in Kotlin Android

3 Answers3