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How to Get Selected Index From List In Kotlin?

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Administrator

by admin , in category: Discussion , 4 months ago

To get the selected index from a list in Kotlin, you can use various methods depending on the context. Here are some common scenarios and how to handle them:


1. Getting Index Based on Value

If you have a value and you want to find its index in the list, you can use the indexOf method:

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val list = listOf("apple", "banana", "cherry")
val selectedItem = "banana"
val selectedIndex = list.indexOf(selectedItem)
println(selectedIndex)  // Output: 1

2. Getting Index in a Loop

If you are iterating through the list and need to know the index of the current item, you can use forEachIndexed:

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val list = listOf("apple", "banana", "cherry")
list.forEachIndexed { index, item ->
    if (item == "banana") {
        println("Index of banana is $index")  // Output: Index of banana is 1
    }
}

3. Using List with a Selection Mechanism (e.g., in a UI Component)

If you are working with a UI component like a RecyclerView or ListView, the selection index is typically handled by the component's adapter. Here’s an example using a RecyclerView:

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class MyAdapter(private val itemList: List<String>, private val itemClickListener: (Int) -> Unit) : RecyclerView.Adapter<MyAdapter.ViewHolder>() {


    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val textView: TextView = itemView.findViewById(R.id.textView)
        
        init {
            itemView.setOnClickListener {
                itemClickListener(adapterPosition)
            }
        }
    }


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_layout, parent, false)
        return ViewHolder(view)
    }


    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.textView.text = itemList[position]
    }


    override fun getItemCount(): Int {
        return itemList.size
    }
}


// Usage in an Activity or Fragment
val myAdapter = MyAdapter(listOf("apple", "banana", "cherry")) { selectedIndex ->
    println("Selected index: $selectedIndex")  // Handle selected index here
}

4. Finding Index with a Condition

If you need to find the index based on a specific condition, you can use indexOfFirst:

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val list = listOf("apple", "banana", "cherry")
val selectedIndex = list.indexOfFirst { it.startsWith("b") }
println(selectedIndex)  // Output: 1

Summary

  • indexOf: Finds the index of a specific item.
  • forEachIndexed: Iterates through the list with access to both item and index.
  • RecyclerView Adapter: Handles index through item click listeners.
  • indexOfFirst: Finds the index based on a condition.

Choose the method that best fits your specific use case.

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