diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/activities/MainActivity.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/activities/MainActivity.kt
index a5b52ce0..8bbd46cd 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/activities/MainActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/activities/MainActivity.kt
@@ -218,7 +218,7 @@ class MainActivity : SimpleActivity(), RefreshContactsListener {
 
     private fun initFragments() {
         viewpager.adapter = ViewPagerAdapter(this)
-        viewpager.setOnPageChangeListener(object : ViewPager.OnPageChangeListener {
+        viewpager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
             override fun onPageScrollStateChanged(state: Int) {
                 if (isSearchOpen) {
                     getCurrentFragment().onSearchQueryChanged("")
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/ContactsAdapter.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/ContactsAdapter.kt
index e2514ef6..fc72ab44 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/ContactsAdapter.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/ContactsAdapter.kt
@@ -27,8 +27,8 @@ import com.simplemobiletools.contacts.models.Contact
 import kotlinx.android.synthetic.main.item_contact_with_number.view.*
 import java.util.*
 
-class ContactsAdapter(activity: SimpleActivity, var contactItems: MutableList<Contact>, val listener: RefreshContactsListener?,
-                      val isFavoritesFragment: Boolean, recyclerView: MyRecyclerView, fastScroller: FastScroller, itemClick: (Any) -> Unit) :
+class ContactsAdapter(activity: SimpleActivity, var contactItems: MutableList<Contact>, private val listener: RefreshContactsListener?,
+                      private val isFavoritesFragment: Boolean, recyclerView: MyRecyclerView, fastScroller: FastScroller, itemClick: (Any) -> Unit) :
         MyRecyclerViewAdapter(activity, recyclerView, fastScroller, itemClick) {
 
     private lateinit var contactDrawable: Drawable
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/FilterContactSourcesAdapter.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/FilterContactSourcesAdapter.kt
index 115eee3e..05bb831a 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/FilterContactSourcesAdapter.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/FilterContactSourcesAdapter.kt
@@ -12,7 +12,7 @@ import com.simplemobiletools.contacts.extensions.config
 import kotlinx.android.synthetic.main.item_filter_contact_source.view.*
 import java.util.*
 
-class FilterContactSourcesAdapter(val activity: SimpleActivity, val contactSources: List<String>, val displayContactSources: Set<String>) :
+class FilterContactSourcesAdapter(val activity: SimpleActivity, private val contactSources: List<String>, private val displayContactSources: Set<String>) :
         RecyclerView.Adapter<FilterContactSourcesAdapter.ViewHolder>() {
     private val itemViews = SparseArray<View>()
     private val selectedPositions = HashSet<Int>()
@@ -66,7 +66,7 @@ class FilterContactSourcesAdapter(val activity: SimpleActivity, val contactSourc
 
     override fun getItemCount() = contactSources.size
 
-    class ViewHolder(view: View, val adapterListener: MyAdapterListener, val activity: SimpleActivity) : RecyclerView.ViewHolder(view) {
+    class ViewHolder(view: View, private val adapterListener: MyAdapterListener, val activity: SimpleActivity) : RecyclerView.ViewHolder(view) {
         fun bindView(contactSource: String): View {
             itemView.apply {
                 filter_contact_source_checkbox.setColors(activity.config.textColor, activity.getAdjustedPrimaryColor(), activity.config.backgroundColor)
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/SelectContactsAdapter.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/SelectContactsAdapter.kt
index 68145cca..cc2d5058 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/SelectContactsAdapter.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/adapters/SelectContactsAdapter.kt
@@ -23,8 +23,8 @@ import com.simplemobiletools.contacts.models.Contact
 import kotlinx.android.synthetic.main.item_add_favorite_with_number.view.*
 import java.util.*
 
-class SelectContactsAdapter(val activity: SimpleActivity, val contacts: List<Contact>, val selectedContacts: ArrayList<String>, val allowPickMultiple: Boolean,
-                            val itemClick: ((Contact) -> Unit)? = null) : RecyclerView.Adapter<SelectContactsAdapter.ViewHolder>() {
+class SelectContactsAdapter(val activity: SimpleActivity, val contacts: List<Contact>, private val selectedContacts: ArrayList<String>, private val allowPickMultiple: Boolean,
+                            private val itemClick: ((Contact) -> Unit)? = null) : RecyclerView.Adapter<SelectContactsAdapter.ViewHolder>() {
     private val itemViews = SparseArray<View>()
     private val selectedPositions = HashSet<Int>()
     private val config = activity.config
@@ -86,8 +86,8 @@ class SelectContactsAdapter(val activity: SimpleActivity, val contacts: List<Con
 
     override fun getItemCount() = contacts.size
 
-    class ViewHolder(view: View, val adapterListener: MyAdapterListener, val activity: SimpleActivity, val showCheckbox: Boolean,
-                     val itemClick: ((Contact) -> Unit)?) : RecyclerView.ViewHolder(view) {
+    class ViewHolder(view: View, private val adapterListener: MyAdapterListener, val activity: SimpleActivity, private val showCheckbox: Boolean,
+                     private val itemClick: ((Contact) -> Unit)?) : RecyclerView.ViewHolder(view) {
         fun bindView(contact: Contact, startNameWithSurname: Boolean, contactDrawable: Drawable, config: Config, showContactThumbnails: Boolean,
                      smallPadding: Int, bigPadding: Int): View {
             itemView.apply {
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/AddFavoritesDialog.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/AddFavoritesDialog.kt
index 884c8be9..c846d0fc 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/AddFavoritesDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/AddFavoritesDialog.kt
@@ -11,7 +11,7 @@ import com.simplemobiletools.contacts.helpers.ContactsHelper
 import com.simplemobiletools.contacts.models.Contact
 import kotlinx.android.synthetic.main.layout_select_contact.view.*
 
-class AddFavoritesDialog(val activity: SimpleActivity, val callback: () -> Unit) {
+class AddFavoritesDialog(val activity: SimpleActivity, private val callback: () -> Unit) {
     private var dialog: AlertDialog? = null
     private var view = activity.layoutInflater.inflate(R.layout.layout_select_contact, null)
     private val config = activity.config
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ChangeSortingDialog.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ChangeSortingDialog.kt
index c791ca61..22a63539 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ChangeSortingDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ChangeSortingDialog.kt
@@ -11,7 +11,7 @@ import com.simplemobiletools.contacts.R
 import com.simplemobiletools.contacts.extensions.config
 import kotlinx.android.synthetic.main.dialog_change_sorting.view.*
 
-class ChangeSortingDialog(val activity: BaseSimpleActivity, val callback: () -> Unit) {
+class ChangeSortingDialog(val activity: BaseSimpleActivity, private val callback: () -> Unit) {
     private var currSorting = 0
     private var config = activity.config
     private var view = activity.layoutInflater.inflate(R.layout.dialog_change_sorting, null)
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ExportContactsDialog.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ExportContactsDialog.kt
index 1df75ded..494ddf1a 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ExportContactsDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ExportContactsDialog.kt
@@ -11,7 +11,7 @@ import com.simplemobiletools.contacts.helpers.ContactsHelper
 import kotlinx.android.synthetic.main.dialog_export_contacts.view.*
 import java.io.File
 
-class ExportContactsDialog(val activity: SimpleActivity, val path: String, val callback: (file: File, contactSources: HashSet<String>) -> Unit) {
+class ExportContactsDialog(val activity: SimpleActivity, val path: String, private val callback: (file: File, contactSources: HashSet<String>) -> Unit) {
 
     init {
         val view = (activity.layoutInflater.inflate(R.layout.dialog_export_contacts, null) as ViewGroup).apply {
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/FilterContactSourcesDialog.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/FilterContactSourcesDialog.kt
index c3f2d5c5..6a516e01 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/FilterContactSourcesDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/FilterContactSourcesDialog.kt
@@ -9,7 +9,7 @@ import com.simplemobiletools.contacts.extensions.config
 import com.simplemobiletools.contacts.helpers.ContactsHelper
 import kotlinx.android.synthetic.main.dialog_filter_contact_sources.view.*
 
-class FilterContactSourcesDialog(val activity: SimpleActivity, val callback: () -> Unit) {
+class FilterContactSourcesDialog(val activity: SimpleActivity, private val callback: () -> Unit) {
     private var dialog: AlertDialog? = null
     private val view = activity.layoutInflater.inflate(R.layout.dialog_filter_contact_sources, null)
 
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ImportContactsDialog.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ImportContactsDialog.kt
index fde2a6fa..a83c9f87 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ImportContactsDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/dialogs/ImportContactsDialog.kt
@@ -13,7 +13,7 @@ import com.simplemobiletools.contacts.helpers.VcfImporter
 import com.simplemobiletools.contacts.helpers.VcfImporter.ImportResult.IMPORT_FAIL
 import kotlinx.android.synthetic.main.dialog_import_contacts.view.*
 
-class ImportContactsDialog(val activity: SimpleActivity, val path: String, val callback: (refreshView: Boolean) -> Unit) {
+class ImportContactsDialog(val activity: SimpleActivity, val path: String, private val callback: (refreshView: Boolean) -> Unit) {
     init {
         val view = (activity.layoutInflater.inflate(R.layout.dialog_import_contacts, null) as ViewGroup).apply {
             import_contacts_title.text = activity.config.lastUsedContactSource
diff --git a/app/src/main/kotlin/com/simplemobiletools/contacts/helpers/Constants.kt b/app/src/main/kotlin/com/simplemobiletools/contacts/helpers/Constants.kt
index 755bfa8e..9bbcb459 100644
--- a/app/src/main/kotlin/com/simplemobiletools/contacts/helpers/Constants.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/contacts/helpers/Constants.kt
@@ -3,50 +3,50 @@ package com.simplemobiletools.contacts.helpers
 import android.provider.ContactsContract.CommonDataKinds
 
 // shared prefs
-val CALL_CONTACT_ON_CLICK = "call_contact_on_click"
-val SHOW_CONTACT_THUMBNAILS = "show_contact_thumbnails"
-val SHOW_PHONE_NUMBERS = "show_phone_numbers"
-val DISPLAY_CONTACT_SOURCES = "display_contact_sources"
-val START_NAME_WITH_SURNAME = "start_name_with_surname"
-val LAST_USED_CONTACT_SOURCE = "last_used_contact_source"
-val LAST_USED_VIEW_PAGER_PAGE = "last_used_view_pager_page"
+const val CALL_CONTACT_ON_CLICK = "call_contact_on_click"
+const val SHOW_CONTACT_THUMBNAILS = "show_contact_thumbnails"
+const val SHOW_PHONE_NUMBERS = "show_phone_numbers"
+const val DISPLAY_CONTACT_SOURCES = "display_contact_sources"
+const val START_NAME_WITH_SURNAME = "start_name_with_surname"
+const val LAST_USED_CONTACT_SOURCE = "last_used_contact_source"
+const val LAST_USED_VIEW_PAGER_PAGE = "last_used_view_pager_page"
 
-val CONTACT_ID = "contact_id"
+const val CONTACT_ID = "contact_id"
 
 // contact photo changes
-val PHOTO_ADDED = 1
-val PHOTO_REMOVED = 2
-val PHOTO_CHANGED = 3
-val PHOTO_UNCHANGED = 4
+const val PHOTO_ADDED = 1
+const val PHOTO_REMOVED = 2
+const val PHOTO_CHANGED = 3
+const val PHOTO_UNCHANGED = 4
 
 // default contact values
-val DEFAULT_EMAIL_TYPE = CommonDataKinds.Email.TYPE_HOME
-val DEFAULT_PHONE_NUMBER_TYPE = CommonDataKinds.Phone.TYPE_MOBILE
-val DEFAULT_EVENT_TYPE = CommonDataKinds.Event.TYPE_BIRTHDAY
+const val DEFAULT_EMAIL_TYPE = CommonDataKinds.Email.TYPE_HOME
+const val DEFAULT_PHONE_NUMBER_TYPE = CommonDataKinds.Phone.TYPE_MOBILE
+const val DEFAULT_EVENT_TYPE = CommonDataKinds.Event.TYPE_BIRTHDAY
 
 // export/import
-val BEGIN_VCARD = "BEGIN:VCARD"
-val END_VCARD = "END:VCARD"
-val N = "N:"
-val TEL = "TEL"
-val BDAY = "BDAY:"
-val ANNIVERSARY = "ANNIVERSARY:"
-val PHOTO = "PHOTO"
-val EMAIL = "EMAIL"
-val ENCODING = "ENCODING"
-val BASE64 = "BASE64"
-val JPEG = "JPEG"
-val VERSION_2_1 = "VERSION:2.1"
+const val BEGIN_VCARD = "BEGIN:VCARD"
+const val END_VCARD = "END:VCARD"
+const val N = "N:"
+const val TEL = "TEL"
+const val BDAY = "BDAY:"
+const val ANNIVERSARY = "ANNIVERSARY:"
+const val PHOTO = "PHOTO"
+const val EMAIL = "EMAIL"
+const val ENCODING = "ENCODING"
+const val BASE64 = "BASE64"
+const val JPEG = "JPEG"
+const val VERSION_2_1 = "VERSION:2.1"
 
 // phone number/email types
-val CELL = "CELL"
-val WORK = "WORK"
-val HOME = "HOME"
-val PREF = "PREF"
-val MAIN = "MAIN"
-val FAX = "FAX"
-val WORK_FAX = "WORK;FAX"
-val HOME_FAX = "HOME;FAX"
-val PAGER = "PAGER"
-val MOBILE = "MOBILE"
-val VOICE = "VOICE"
+const val CELL = "CELL"
+const val WORK = "WORK"
+const val HOME = "HOME"
+const val PREF = "PREF"
+const val MAIN = "MAIN"
+const val FAX = "FAX"
+const val WORK_FAX = "WORK;FAX"
+const val HOME_FAX = "HOME;FAX"
+const val PAGER = "PAGER"
+const val MOBILE = "MOBILE"
+const val VOICE = "VOICE"