prebuilts/gradle/RecyclerView/kotlinApp/app/src/main/java/com/example/android/recyclerview/RecyclerViewFragment.kt

/*
* Copyright (C) 2017 The Android Open Source Project
*
* 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.
*/

package com.example.android.recyclerview

import android.os.Bundle
import android.support.v4.app.Fragment
import android.support.v7.widget.GridLayoutManager
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.RadioButton

/**
 * Demonstrates the use of [RecyclerView] with a [LinearLayoutManager] and a
 * [GridLayoutManager].
 */
class RecyclerViewFragment : Fragment() {

    private lateinit var currentLayoutManagerType: LayoutManagerType
    private lateinit var recyclerView: RecyclerView
    private lateinit var layoutManager: RecyclerView.LayoutManager
    private lateinit var dataset: Array<String>

    enum class LayoutManagerType { GRID_LAYOUT_MANAGER, LINEAR_LAYOUT_MANAGER }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // Initialize dataset, this data would usually come from a local content provider or
        // remote server.
        initDataset()
    }

    override fun onCreateView(inflater: LayoutInflater,
                              container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        val rootView = inflater.inflate(R.layout.recycler_view_frag,
                container, false).apply { tag = TAG}

        recyclerView = rootView.findViewById(R.id.recyclerView)

        // LinearLayoutManager is used here, this will layout the elements in a similar fashion
        // to the way ListView would layout elements. The RecyclerView.LayoutManager defines how
        // elements are laid out.
        layoutManager = LinearLayoutManager(activity)

        currentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER

        if (savedInstanceState != null) {
            // Restore saved layout manager type.
            currentLayoutManagerType = savedInstanceState
                    .getSerializable(KEY_LAYOUT_MANAGER) as LayoutManagerType
        }
        setRecyclerViewLayoutManager(currentLayoutManagerType)

        // Set CustomAdapter as the adapter for RecyclerView.
        recyclerView.adapter = CustomAdapter(dataset)

        rootView.findViewById<RadioButton>(R.id.linear_layout_rb).setOnClickListener{
            setRecyclerViewLayoutManager(LayoutManagerType.LINEAR_LAYOUT_MANAGER)
        }

        rootView.findViewById<RadioButton>(R.id.grid_layout_rb).setOnClickListener{
            setRecyclerViewLayoutManager(LayoutManagerType.GRID_LAYOUT_MANAGER)
        }

        return rootView
    }

    /**
     * Set RecyclerView's LayoutManager to the one given.
     *
     * @param layoutManagerType Type of layout manager to switch to.
     */
    private fun setRecyclerViewLayoutManager(layoutManagerType: LayoutManagerType) {
        var scrollPosition = 0

        // If a layout manager has already been set, get current scroll position.
        if (recyclerView.layoutManager != null) {
            scrollPosition = (recyclerView.layoutManager as LinearLayoutManager)
                    .findFirstCompletelyVisibleItemPosition()
        }

        when (layoutManagerType) {
            RecyclerViewFragment.LayoutManagerType.GRID_LAYOUT_MANAGER -> {
                layoutManager = GridLayoutManager(activity, SPAN_COUNT)
                currentLayoutManagerType = LayoutManagerType.GRID_LAYOUT_MANAGER
            }
            RecyclerViewFragment.LayoutManagerType.LINEAR_LAYOUT_MANAGER -> {
                layoutManager = LinearLayoutManager(activity)
                currentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER
            }
        }

        with(recyclerView) {
            layoutManager = this@RecyclerViewFragment.layoutManager
            scrollToPosition(scrollPosition)
        }

    }

    override fun onSaveInstanceState(savedInstanceState: Bundle) {

        // Save currently selected layout manager.
        savedInstanceState.putSerializable(KEY_LAYOUT_MANAGER, currentLayoutManagerType)
        super.onSaveInstanceState(savedInstanceState)
    }

    /**
     * Generates Strings for RecyclerView's adapter. This data would usually come
     * from a local content provider or remote server.
     */
    private fun initDataset() {
        dataset = Array(DATASET_COUNT, {i -> "This is element # $i"})
    }

    companion object {
        private val TAG = "RecyclerViewFragment"
        private val KEY_LAYOUT_MANAGER = "layoutManager"
        private val SPAN_COUNT = 2
        private val DATASET_COUNT = 60
    }
}