properly calculate scrollbar height

app/build.gradle

@@ -43,5 +43,5 @@ android {
 }
 
 dependencies {
-    implementation 'com.github.SimpleMobileTools:Simple-Commons:8b339d6e4b'
+    implementation 'com.github.SimpleMobileTools:Simple-Commons:01841778a4'
 }

app/src/main/AndroidManifest.xml

@@ -32,6 +32,7 @@
 
         <activity
             android:name=".activities.MainActivity"
+            android:configChanges="orientation|keyboardHidden|screenSize"
             android:exported="true"
             android:theme="@style/LauncherTheme" />
 

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

@@ -5,6 +5,7 @@ import android.content.Context
 import android.content.Intent
 import android.content.pm.LauncherApps
 import android.content.pm.PackageManager
+import android.content.res.Configuration
 import android.graphics.Color
 import android.graphics.drawable.Drawable
 import android.os.Bundle
@@ -17,6 +18,7 @@ import com.simplemobiletools.commons.views.MyGridLayoutManager
 import com.simplemobiletools.launcher.BuildConfig
 import com.simplemobiletools.launcher.R
 import com.simplemobiletools.launcher.adapters.LaunchersAdapter
+import com.simplemobiletools.launcher.extensions.getColumnCount
 import com.simplemobiletools.launcher.models.AppLauncher
 import kotlinx.android.synthetic.main.activity_main.*
 
@@ -40,6 +42,18 @@ class MainActivity : SimpleActivity() {
         setupNavigationBar()
     }
 
+    override fun onConfigurationChanged(newConfig: Configuration) {
+        super.onConfigurationChanged(newConfig)
+        launchers_grid.scrollToPosition(0)
+        launchers_fastscroller.resetManualScrolling()
+        setupNavigationBar()
+
+        val layoutManager = launchers_grid.layoutManager as MyGridLayoutManager
+        layoutManager.spanCount = getColumnCount()
+        val launchers = (launchers_grid.adapter as LaunchersAdapter).launchers
+        setupAdapter(launchers)
+    }
+
     @SuppressLint("WrongConstant")
     private fun getLaunchers() {
         val allApps = ArrayList<AppLauncher>()
@@ -79,17 +93,12 @@ class MainActivity : SimpleActivity() {
         launchers.sortBy { it.title.toLowerCase() }
 
         val layoutManager = launchers_grid.layoutManager as MyGridLayoutManager
-        layoutManager.spanCount = if (portrait) {
-            resources.getInteger(R.integer.portrait_column_count)
-        } else {
-            resources.getInteger(R.integer.landscape_column_count)
-        }
-
+        layoutManager.spanCount = getColumnCount()
         setupAdapter(launchers)
     }
 
     private fun setupAdapter(launchers: ArrayList<AppLauncher>) {
-        LaunchersAdapter(this, launchers) {
+        LaunchersAdapter(this, launchers, launchers_fastscroller) {
 
         }.apply {
             launchers_grid.adapter = this

app/src/main/kotlin/com/simplemobiletools/launcher/adapters/LaunchersAdapter.kt

@@ -3,6 +3,7 @@ package com.simplemobiletools.launcher.adapters
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.view.ViewTreeObserver
 import androidx.recyclerview.widget.RecyclerView
 import com.qtalk.recyclerviewfastscroller.RecyclerViewFastScroller
 import com.simplemobiletools.commons.extensions.getProperTextColor
@@ -10,16 +11,20 @@ import com.simplemobiletools.commons.extensions.portrait
 import com.simplemobiletools.commons.extensions.realScreenSize
 import com.simplemobiletools.launcher.R
 import com.simplemobiletools.launcher.activities.SimpleActivity
+import com.simplemobiletools.launcher.extensions.getColumnCount
 import com.simplemobiletools.launcher.models.AppLauncher
 import kotlinx.android.synthetic.main.item_launcher_label.view.*
 
 class LaunchersAdapter(
     val activity: SimpleActivity,
     val launchers: ArrayList<AppLauncher>,
+    val fastScroller: RecyclerViewFastScroller,
     val itemClick: (Any) -> Unit
 ) : RecyclerView.Adapter<LaunchersAdapter.ViewHolder>(), RecyclerViewFastScroller.OnPopupTextUpdate {
+
     private var textColor = activity.getProperTextColor()
     private var iconPadding = 0
+    private var wasManualScrollPositionSet = false
 
     init {
         calculateIconWidth()
@@ -57,6 +62,19 @@ class LaunchersAdapter(
                 setOnClickListener { itemClick(launcher) }
             }
 
+            if (!wasManualScrollPositionSet) {
+                itemView.launcher_holder.viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
+                    override fun onGlobalLayout() {
+                        itemView.launcher_holder.viewTreeObserver.removeOnGlobalLayoutListener(this)
+                        if (!wasManualScrollPositionSet) {
+                            val rowCount = Math.ceil(launchers.size / activity.getColumnCount().toDouble()).toInt()
+                            fastScroller.fullContentHeight = rowCount * itemView.height
+                            fastScroller.calculateScrollPositionManually = true
+                        }
+                    }
+                })
+            }
+
             return itemView
         }
     }

app/src/main/kotlin/com/simplemobiletools/launcher/extensions/Context.kt

@@ -1,6 +1,16 @@
 package com.simplemobiletools.launcher.extensions
 
 import android.content.Context
+import com.simplemobiletools.commons.extensions.portrait
+import com.simplemobiletools.launcher.R
 import com.simplemobiletools.launcher.helpers.Config
 
 val Context.config: Config get() = Config.newInstance(applicationContext)
+
+fun Context.getColumnCount(): Int {
+    return if (portrait) {
+        resources.getInteger(R.integer.portrait_column_count)
+    } else {
+        resources.getInteger(R.integer.landscape_column_count)
+    }
+}