How to pass function as parameter from java to kotlin method?

Question

I have a Kotlin Code:

fun showAdWithCallback(callback:() -> Unit) {
    if (AdsPrefs.shouldShowInterstitialAd()) {
        mInterstitialAd.show()
        this.callback = callback
    } else {
        callback()
    }
}

Now I want to call this method from a Java Class. I am confused about how to call this. Here is what I tried

  showAdWithCallback(() -> {
        return null;
    });

But it shows following error.

how about https://stackoverflow.com/questions/37828790/why-do-i-have-to-return-unit-instance-when-implementing-in-java-a-kotlin-functio — P.Juni, Jul 30 '19 at 07:02
Check out here https://stackoverflow.com/questions/16120697/kotlin-how-to-pass-a-function-as-parameter-to-another — Vipul Prajapati, Jul 30 '19 at 07:07
@P.Juni The reference you gave has a callback that accept one argument, but I have a callback without any parameters. So that doesn't solve the problem. — Prajeet Shrestha, Jul 30 '19 at 07:10
@VipulPrajapati The reference you gave has examples of passing function from a kotlin code to kotlin functions, what I want here is to let my java class use function in kotlin class (which accepts function as a argument) — Prajeet Shrestha, Jul 30 '19 at 07:13
https://stackoverflow.com/questions/4685563/how-to-pass-a-function-as-a-parameter-in-java — P.Juni, Jul 30 '19 at 07:15
@PrajeetShrestha please share the code before your `showAdWithCallback` — Bartek Lipinski, Jul 30 '19 at 07:15
@BartekLipinski. Oh u got me........I had return statement just before showAdWithCallback. I was randomly embedding showAdWithCallback to tryout, overlooked the return statement. Thank u so much. You can put it as a answer I will accept and upvote. — Prajeet Shrestha, Jul 30 '19 at 07:24

score 13 · Accepted Answer · answered Jul 30 '19 at 08:04

13

The error message is caused by the code before your:

showAdWithCallback(() -> {
        return null;
});

answered Jul 30 '19 at 08:04

Bartek Lipinski

30,698
10
94
132

score 1 · Answer 2 · answered Jul 30 '19 at 07:48

1

Call kotlin object and call function

kotlinobject.INSTANCE.showAdWithCallback(()->{
    return null;
})

answered Jul 30 '19 at 07:48

Yogesh Bangar

480
4
12

score 0 · Answer 3 · answered Jul 30 '19 at 07:44

0

callback:() -> Unit

It's a typically runnable - zero arguments, without return value

answered Jul 30 '19 at 07:44

tragos777

1
1

How to pass function as parameter from java to kotlin method?

3 Answers3