Custom Spinner to differentiate between user selected and programmatically selected item in Kotlin for Android.

CustomSpinner.kt

/*
 * Copyright 2018 Andrius Baruckis www.baruckis.com
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.content.Context
import android.util.AttributeSet
import android.view.View
import android.widget.Spinner
import android.widget.AdapterView


/**
 * Custom Spinner to differentiate between user selected and programmatically selected item.
 * 
 * Call [CustomSpinner.programmaticallySetPosition] to set it programmatically.
 * Call [CustomSpinner.setSelection] to set it user selected.
 */
class CustomSpinner : Spinner, AdapterView.OnItemSelectedListener {

    private var mListener: OnItemSelectedListener? = null

    /**
     * Used to ascertain whether the user selected an item on spinner (and not programmatically).
     */
    private var mUserActionOnSpinner = true

    override fun onItemSelected(parent: AdapterView<*>, view: View, position: Int, id: Long) {

        if (mListener != null) {

            mListener!!.onItemSelected(parent, view, position, id, mUserActionOnSpinner)
        }
        // Reset variable, so that it will always be true unless tampered with.
        mUserActionOnSpinner = true
    }

    override fun onNothingSelected(parent: AdapterView<*>) {
        if (mListener != null)
            mListener!!.onNothingSelected(parent)
    }

    interface OnItemSelectedListener {
        /**
         *
         * Callback method to be invoked when an item in this view has been
         * selected. This callback is invoked only when the newly selected
         * position is different from the previously selected position or if
         * there was no selected item.
         *
         * Impelmenters can call getItemAtPosition(position) if they need to access the
         * data associated with the selected item.
         *
         * @param parent The AdapterView where the selection happened.
         * @param view The view within the AdapterView that was clicked.
         * @param position The position of the view in the adapter.
         * @param id The row id of the item that is selected.
         */
        fun onItemSelected(parent: AdapterView<*>, view: View, position: Int, id: Long, userSelected: Boolean)

        /**
         * Callback method to be invoked when the selection disappears from this
         * view. The selection can disappear for instance when touch is activated
         * or when the adapter becomes empty.
         *
         * @param parent The AdapterView that now contains no selected item.
         */
        fun onNothingSelected(parent: AdapterView<*>)
    }

    fun programmaticallySetPosition(pos: Int, animate: Boolean = true) {
        mUserActionOnSpinner = false
        setSelection(pos, animate)
    }

    fun setCustomOnItemSelectedListener(listener: OnItemSelectedListener) {
        mListener = listener
    }

    constructor(context: Context) : super(context) {
        super.setOnItemSelectedListener(this)
    }

    constructor(context: Context, mode: Int) : super(context, mode) {
        super.setOnItemSelectedListener(this)
    }

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {
        super.setOnItemSelectedListener(this)
    }

    constructor(context: Context, attrs: AttributeSet, defStyle: Int) : super(context, attrs, defStyle) {
        super.setOnItemSelectedListener(this)
    }

    constructor(context: Context, attrs: AttributeSet, defStyle: Int, mode: Int) : super(context, attrs, defStyle, mode) {
        super.setOnItemSelectedListener(this)
    }
}