CODEWITHSUNDEEP
androidkotlin
George Udosen
George Udosen

Reputation: 936

Understanding the parts of a kotlin function

I have this kotlin function I am using to access data after making a http request using the fuel library in android, from a tutorial I am following but certain parts of this function are strange to me as I am learning kotlin:

fun search(term: String, skip: Int, take: Int, responseHandler: (result: WikiResult) -> Unit?) {
        Urls.getSearchUrl(term, skip, take).httpGet()
            .responseObject(WikipediaDataDeserializer()) { _, response, result ->
                if (response.statusCode != 200) {
                    throw Exception("Unable to get articles")
                }
                val(data, _) = result
                responseHandler.invoke(data as @ParameterName(name = "result") WikiResult)
            }
    }

These I understand so far:

but I can't understand most of this part:

.responseObject(WikipediaDataDeserializer()) { _, response, result ->
                if (response.statusCode != 200) {
                    throw Exception("Unable to get articles")
                } #<-- this I know throws an exception if the response isn't a 200
                val(data, _) = result
                responseHandler.invoke(data as @ParameterName(name = "result") WikiResult)
            }

Upvotes: 0

Views: 83

Answers (1)

a_local_nobody
a_local_nobody

Reputation: 8191

responseHandler: (result: WikiResult) -> Unit? is a callback (lambda) function.

It says that it will take in a result: WikiResult and give this to whatever is calling it.

.responseObject(WikipediaDataDeserializer()) { _, response, result ->
                if (response.statusCode != 200) {
                    throw Exception("Unable to get articles")
                } #<-- this I know throws an exception if the response isn't a 200
                val(data, _) = result
                responseHandler.invoke(data as @ParameterName(name = "result") WikiResult)
            }

here, where you are calling responseObject(WikipediaDataDeserializer()), you are specifying how to handle another lambda function.

{ _, response, result -> is simply saying that you are getting 3 values, the first one you don't care for, you're not using it, so you can rename it to _, then your response object and your result object you will be using, so they have been given those names accordingly.

Edit

you have to look at it like 2 different methods :

when you call search, you'll do this : 

search("term", 0, 0) { 
 //this is your responseHandler: (result: WikiResult) -> Unit?)
 // in here, you'll get a result: WikiResult
}

similarly, when you call this :

    Urls.getSearchUrl(term, skip, take).httpGet()
                .responseObject(WikipediaDataDeserializer()) { _, response, result -> ...

this entire chain has a callback you get back, and it gives you 3 values, as explained in my answer above.

val(data, _) = result is known as Destructuring Declarations https://kotlinlang.org/docs/reference/multi-declarations.html

but yes, you're correct in your understanding, we are using the response of this callback, destructing it and then triggering the callback with this data

Upvotes: 1

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