Make width of horizontal recycler view items 70% of screen width

If you want the first item to be left-aligned (i.e., reproduce what’s in the screenshot), subclass LinearLayoutManager and override the three generate*LayoutParams methods. Here’s how I did it: https://gist.github.com/bolot/6f1838d29d5b8a87b5fcadbeb53fb6f0.

class PeekingLinearLayoutManager : LinearLayoutManager {
    @JvmOverloads
    constructor(context: Context?, @RecyclerView.Orientation orientation: Int = RecyclerView.VERTICAL, reverseLayout: Boolean = false) : super(context, orientation, reverseLayout)

    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)

    override fun generateDefaultLayoutParams() =
        scaledLayoutParams(super.generateDefaultLayoutParams())

    override fun generateLayoutParams(lp: ViewGroup.LayoutParams?) =
        scaledLayoutParams(super.generateLayoutParams(lp))

    override fun generateLayoutParams(c: Context?, attrs: AttributeSet?) =
        scaledLayoutParams(super.generateLayoutParams(c, attrs))

    private fun scaledLayoutParams(layoutParams: RecyclerView.LayoutParams) =
        layoutParams.apply {
            when(orientation) {
                HORIZONTAL -> width = (horizontalSpace * ratio).toInt()
                VERTICAL -> height = (verticalSpace * ratio).toInt()
            }
        }

    private val horizontalSpace get() = width - paddingStart - paddingEnd

    private val verticalSpace get() = height - paddingTop - paddingBottom

    private val ratio = 0.9f // change to 0.7f for 70%
}

This solution is based on/inspired by the spanning (i.e., fit all items to screen) linear layout manager https://gist.github.com/heinrichreimer/39f9d2f9023a184d96f8.

Btw, if you just want to show the items to the left and to the right, while the current item is centered, you can add padding to the recycler view and set clipToPadding to false. In this case you don’t even need a custom layout manager.

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recycler_view"
    android:paddingStart="16dp"
    android:paddingEnd="16dp"
    android:clipToPadding="false"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager">