Kotlin lambda function with arguments

Question

I am currently developing an Android application that uses the Retrofit library for REST api usage.

For instance, I have the following code from MainActivity.kt :

fun userLogin(){
    calls.userLogin() { updateUiComponents() }
    }

fun updateUiComponents(){
    Toast.makeText(applicationContext, "LAMBDA EXECUTED",Toast.LENGTH_SHORT).show()
    }

And I have in a separate file the definition of the Retrofit calls:

fun userLogin(postActionMethod: () -> Unit){
    val call = service.userLogin()
    call.enqueue(object : Callback<LoginResponse>{
        override fun onFailure(call: Call<LoginResponse>?, t: Throwable?) {
            Log.i("ERROR RUNNING CALL", t?.message.toString())
        }

        override fun onResponse(call: Call<LoginResponse>?, response: Response<LoginResponse>?) {
            postActionMethod()
        }
    })
}

After the Retrofit call is implemented and it is successful, reaching the onResponse method, I would like to send the Response object as a parameter of the lambda function back to the MainAcativity.kt. From the MainActivity.kt, the lambda function would use this information to perform some specific task.

Is that a way of defining a lambda function like this, with arguments? If it is the case, how can I pass the lambda function as a parameter like done on the following line:

calls.userLogin(body) { updateUiComponents() }

Thank u!

Alberto S. · Accepted Answer · 2018-09-25 15:17:06Z

2

I don't know if I get what your problem is but a lambda does not need to do not have any parameter. You can easily do something like

fun userLogin(postActionMethod: (Response<LoginResponse>?) -> Unit){
    val call = service.userLogin()
    call.enqueue(object : Callback<LoginResponse>{
        override fun onFailure(call: Call<LoginResponse>?, t: Throwable?) {
            Log.i("ERROR RUNNING CALL", t?.message.toString())
        }

        override fun onResponse(call: Call<LoginResponse>?, response: Response<LoginResponse>?) {
            postActionMethod(response)
        }
    })
}

so you consume it with

fun userLogin(){
    calls.userLogin() { updateUiComponents(it) }
    }

fun updateUiComponents(response: Response<LoginResponse>?){
    Toast.makeText(applicationContext, "LAMBDA EXECUTED",Toast.LENGTH_SHORT).show()
    }

answered Sep 25, 2018 at 15:17

Alberto S.

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4 Comments

Lajos Neto Over a year ago

That's exactly what I need! I tried the change you commented but it did not work. The problem is exactly at this line: calls.userLogin() { updateUiComponents(it) ... It requires that I pass the response parameter on this line and using "it" as you commented did not work :/

Alberto S. Over a year ago

You can use it to refer to the only param of a lambda. I just wrote an equivalent code and it worked for me

Lajos Neto Over a year ago

Sorry, I forgot to update the code from fun userLogin(postActionMethod: (Response<LoginResponse>?) -> Unit) . And if I want to pass more than one parameter, I can keep the same syntax, right? For example: postActionMethod(response1, response2)

Alberto S. Over a year ago

Yes, you probably want to check the Higher-Order Functions documentation. If the answer solved your problem consider marking it as correct

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