adding an initial implementation of fastscroller with letters

app/build.gradle

@@ -61,6 +61,7 @@ dependencies {
     implementation 'joda-time:joda-time:2.10.1'
     implementation 'androidx.constraintlayout:constraintlayout:2.0.0-beta2'
     implementation 'com.googlecode.ez-vcard:ez-vcard:0.10.5'
+    implementation 'com.reddit:indicator-fast-scroll:1.2.1'
 
     kapt "androidx.room:room-compiler:2.2.2"
     implementation "androidx.room:room-runtime:2.2.2"

app/src/main/kotlin/com/simplemobiletools/contacts/pro/extensions/String.kt

@@ -35,3 +35,5 @@ fun String.getDateTimeFromDateString(viewToUpdate: TextView? = null): DateTime {
 }
 
 fun String.normalizeNumber() = PhoneNumberUtils.normalizeNumber(this)
+
+fun String.areLettersOnly() = matches(Regex("[a-zA-Z]+"))

app/src/main/kotlin/com/simplemobiletools/contacts/pro/fragments/MyViewPagerFragment.kt

@@ -5,6 +5,7 @@ import android.content.Intent
 import android.util.AttributeSet
 import android.view.ViewGroup
 import androidx.coordinatorlayout.widget.CoordinatorLayout
+import com.reddit.indicatorfastscroll.FastScrollItemIndicator
 import com.simplemobiletools.commons.adapters.MyRecyclerViewAdapter
 import com.simplemobiletools.commons.extensions.*
 import com.simplemobiletools.commons.helpers.SORT_BY_FIRST_NAME
@@ -16,6 +17,7 @@ import com.simplemobiletools.contacts.pro.activities.MainActivity
 import com.simplemobiletools.contacts.pro.activities.SimpleActivity
 import com.simplemobiletools.contacts.pro.adapters.ContactsAdapter
 import com.simplemobiletools.contacts.pro.adapters.GroupsAdapter
+import com.simplemobiletools.contacts.pro.extensions.areLettersOnly
 import com.simplemobiletools.contacts.pro.extensions.config
 import com.simplemobiletools.contacts.pro.extensions.getVisibleContactSources
 import com.simplemobiletools.contacts.pro.helpers.*
@@ -23,6 +25,14 @@ import com.simplemobiletools.contacts.pro.interfaces.RefreshContactsListener
 import com.simplemobiletools.contacts.pro.models.Contact
 import com.simplemobiletools.contacts.pro.models.Group
 import kotlinx.android.synthetic.main.fragment_layout.view.*
+import kotlinx.android.synthetic.main.fragment_layout.view.fragment_fab
+import kotlinx.android.synthetic.main.fragment_layout.view.fragment_list
+import kotlinx.android.synthetic.main.fragment_layout.view.fragment_placeholder
+import kotlinx.android.synthetic.main.fragment_layout.view.fragment_placeholder_2
+import kotlinx.android.synthetic.main.fragment_layout.view.fragment_wrapper
+import kotlinx.android.synthetic.main.fragment_letters_layout.view.*
+import java.util.*
+import kotlin.collections.ArrayList
 
 abstract class MyViewPagerFragment(context: Context, attributeSet: AttributeSet) : CoordinatorLayout(context, attributeSet) {
     protected var activity: SimpleActivity? = null
@@ -35,6 +45,7 @@ abstract class MyViewPagerFragment(context: Context, attributeSet: AttributeSet)
 
     var skipHashComparing = false
     var forceListRedraw = false
+    var wasLetterFastScrollerSetup = false
 
     fun setupFragment(activity: SimpleActivity) {
         config = activity.config
@@ -139,6 +150,23 @@ abstract class MyViewPagerFragment(context: Context, attributeSet: AttributeSet)
         } else {
             setupContactsFavoritesAdapter(contacts)
             contactsIgnoringSearch = (fragment_list?.adapter as? ContactsAdapter)?.contactItems ?: ArrayList()
+
+            if (!wasLetterFastScrollerSetup) {
+                wasLetterFastScrollerSetup = true
+                letter_fastscroller.setupWithRecyclerView(fragment_list, { position ->
+                    try {
+                        val name = contacts[position].getNameToDisplay()
+                        var character = if (name.isNotEmpty()) name.substring(0, 1) else ""
+                        if (!character.areLettersOnly()) {
+                            character = "#"
+                        }
+
+                        FastScrollItemIndicator.Text(character.toUpperCase(Locale.getDefault()))
+                    } catch (e: Exception) {
+                        FastScrollItemIndicator.Text("")
+                    }
+                })
+            }
         }
     }
 

app/src/main/res/layout/fragment_letters_layout.xml

@@ -42,6 +42,13 @@
             android:scrollbars="none"
             app:layoutManager="com.simplemobiletools.commons.views.MyLinearLayoutManager"/>
 
+        <com.reddit.indicatorfastscroll.FastScrollerView
+            android:id="@+id/letter_fastscroller"
+            android:layout_width="32dp"
+            android:layout_height="match_parent"
+            android:paddingBottom="@dimen/activity_margin"
+            android:layout_alignParentEnd="true" />
+
     </RelativeLayout>
 
     <com.simplemobiletools.commons.views.MyFloatingActionButton