remember the scroll state when browsing between folders

app/src/main/kotlin/com/simplemobiletools/filemanager/Constants.kt

@@ -1,6 +1,7 @@
 package com.simplemobiletools.filemanager
 
 val PATH = "path"
+val SCROLL_STATE = "scroll_state"
 
 // shared preferences
 val PREFS_KEY = "File Manager"

app/src/main/kotlin/com/simplemobiletools/filemanager/activities/MainActivity.kt

@@ -5,11 +5,13 @@ import android.content.Intent
 import android.content.pm.PackageManager
 import android.os.Bundle
 import android.os.Handler
+import android.os.Parcelable
 import android.support.v4.app.ActivityCompat
 import android.view.Menu
 import android.view.MenuItem
 import com.simplemobiletools.filemanager.PATH
 import com.simplemobiletools.filemanager.R
+import com.simplemobiletools.filemanager.SCROLL_STATE
 import com.simplemobiletools.filemanager.fragments.ItemsFragment
 import com.simplemobiletools.filepicker.dialogs.StoragePickerDialog
 import com.simplemobiletools.filepicker.extensions.getInternalStoragePath
@@ -19,9 +21,12 @@ import com.simplemobiletools.filepicker.models.FileDirItem
 import com.simplemobiletools.filepicker.views.Breadcrumbs
 import kotlinx.android.synthetic.main.activity_main.*
 import java.io.File
+import java.util.*
 
 class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Breadcrumbs.BreadcrumbsListener {
     var mBasePath = getInternalStoragePath()
+    var latestFragment: ItemsFragment? = null
+    var mScrollStates = HashMap<String, Parcelable>()
 
     companion object {
         private val STORAGE_PERMISSION = 1
@@ -59,10 +64,18 @@ class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Br
         val bundle = Bundle()
         bundle.putString(PATH, path)
 
-        val fragment = ItemsFragment()
-        fragment.arguments = bundle
-        fragment.setListener(this)
-        supportFragmentManager.beginTransaction().replace(R.id.fragment_holder, fragment).addToBackStack(path).commitAllowingStateLoss()
+        if (mScrollStates.containsKey(path.trimEnd('/'))) {
+            bundle.putParcelable(SCROLL_STATE, mScrollStates[path.trimEnd('/')])
+        }
+
+        if (latestFragment != null) {
+            mScrollStates.put(latestFragment!!.mPath.trimEnd('/'), latestFragment!!.getScrollState())
+        }
+
+        latestFragment = ItemsFragment()
+        latestFragment!!.arguments = bundle
+        latestFragment!!.setListener(this)
+        supportFragmentManager.beginTransaction().replace(R.id.fragment_holder, latestFragment).addToBackStack(path).commitAllowingStateLoss()
     }
 
     override fun onCreateOptionsMenu(menu: Menu): Boolean {

app/src/main/kotlin/com/simplemobiletools/filemanager/fragments/ItemsFragment.kt

@@ -5,7 +5,9 @@ import android.content.Intent
 import android.graphics.Color
 import android.net.Uri
 import android.os.Bundle
+import android.os.Parcelable
 import android.support.design.widget.Snackbar
+import android.support.v7.widget.LinearLayoutManager
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
@@ -13,6 +15,7 @@ import android.webkit.MimeTypeMap
 import com.simplemobiletools.filemanager.Config
 import com.simplemobiletools.filemanager.PATH
 import com.simplemobiletools.filemanager.R
+import com.simplemobiletools.filemanager.SCROLL_STATE
 import com.simplemobiletools.filemanager.activities.SimpleActivity
 import com.simplemobiletools.filemanager.adapters.ItemsAdapter
 import com.simplemobiletools.filemanager.dialogs.CreateNewItemDialog
@@ -31,8 +34,8 @@ class ItemsFragment : android.support.v4.app.Fragment(), ItemsAdapter.ItemOperat
     lateinit var mConfig: Config
     lateinit var mToBeDeleted: MutableList<String>
 
-    private var mPath = ""
     private var mShowHidden = false
+    var mPath = ""
 
     override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?) =
             inflater!!.inflate(R.layout.items_fragment, container, false)!!
@@ -87,8 +90,14 @@ class ItemsFragment : android.support.v4.app.Fragment(), ItemsAdapter.ItemOperat
         } else {
             (currAdapter as ItemsAdapter).updateItems(mItems)
         }
+
+        getRecyclerLayoutManager().onRestoreInstanceState(arguments.getParcelable<Parcelable>(SCROLL_STATE))
     }
 
+    fun getRecyclerLayoutManager() = (items_list.layoutManager as LinearLayoutManager)
+
+    fun getScrollState() = getRecyclerLayoutManager().onSaveInstanceState()
+
     fun setListener(listener: ItemInteractionListener) {
         mListener = listener
     }