Kotlin RecyclerView Adapter multiple callback functions

June 3, 2022

How do I have multiple callback function back to the Activity/Fragment of a RecyclerView?

I have multiple options for each item in the RecyclerView (Edit, Delete, CheckedAsComplete, View) and I would like to have callback function for each of them in the Activity/Fragment of the RecyclerView.

Here is a link of how I got one callback in the Adapter: https://www.geeksforgeeks.org/kotlin-lambda-functions-for-recyclerview-adapter-callbacks-in-android/

I just need to know if it is possible to have multiple callbacks in the adapter and if so, how do I implement it?

My Activity’s Adapter Code:

val adapter = ProductAdapter(this) {
    deleteProduct(it),
    editProduct(it),
    viewProduct(it),
    checkAsComplete(it)
}

Here is my Adapter’s Constructor:

class ProductAdapter(
    private var context: Context,
    private val deleteProduct: (ItemTable) -> Unit,
    private val editProduct: (ItemTable) -> Unit,
    private val viewProduct: (ItemTable) -> Unit,
    private val checkedAsComplete: (ItemTable) -> Unit
): RecyclerView.Adapter<ProductAdapter.ItemProductViewHolder>() {
    // Rest of RecyclerView Adapter Code
}

I’m pretty new to kotlin so I would really appreciate your help!

>Solution :

You can use curly braces out only for the last callback of the list.

Assuming you declared the following methods in your activity :

fun deleteProduct(itemTable: ItemTable)
fun editProduct(itemTable: ItemTable)
fun checkAsComplete(itemTable: ItemTable)
fun viewProduct(itemTable: ItemTable)

You can use named parameters and you have two choices

With method reference

val adapter = ProductAdapter(
    context = this,
    deleteProduct = ::deleteProduct,
    editProduct  = ::editProduct,
    viewProduct = ::viewProduct,
    checkAsComplete = ::checkAsComplete
)

With lambda

val adapter = ProductAdapter(
    context = this,
    deleteProduct = { deleteProduct(it) },
    editProduct  = { editProduct(it) },
    viewProduct = { viewProduct(it) },
    checkAsComplete = { checkAsComplete(it) }
)