try to save the state of the history.

app/src/main/java/me/zobrist/tichucounter/History.kt

@@ -1,8 +1,15 @@
 package me.zobrist.tichucounter
 
-class History {
+import android.os.Parcel
+import android.os.Parcelable
+
+class History() : Parcelable {
     private var scores: ArrayList<Round> = ArrayList()
 
+    constructor(parcel: Parcel) : this(){
+        scores = parcel.readSerializable() as ArrayList<Round>
+    }
+
     fun getScoreA(): Int {
         var tempScore = 0
         scores.forEach {
@@ -52,4 +59,23 @@ class History {
     fun isEmpty(): Boolean {
         return scores.isEmpty()
     }
+
+    override fun writeToParcel(parcel: Parcel, flags: Int) {
+        parcel.writeSerializable(scores)
+    }
+
+    override fun describeContents(): Int {
+        return 0
+    }
+
+    companion object CREATOR : Parcelable.Creator<History> {
+        override fun createFromParcel(parcel: Parcel): History {
+            return History(parcel)
+        }
+
+        override fun newArray(size: Int): Array<History?> {
+            return arrayOfNulls(size)
+        }
+    }
+
 }

app/src/main/java/me/zobrist/tichucounter/MainActivity.kt

@@ -24,6 +24,7 @@ class MainActivity : AppCompatActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+        history = savedInstanceState?.getParcelable("history")!!
         setContentView(R.layout.activity_main)
         setSupportActionBar(findViewById(R.id.toolbar))
         inputTeamA.setRawInputType(InputType.TYPE_NULL)
@@ -236,6 +237,11 @@ class MainActivity : AppCompatActivity() {
         }
     }
 
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        outState.putParcelable("history", history)
+    }
+
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
         // Inflate the menu; this adds items to the action bar if it is present.
         menuInflater.inflate(R.menu.menu_main, menu)
@@ -267,8 +273,7 @@ class MainActivity : AppCompatActivity() {
 
     }
 
-    private fun updateView()
-    {
+    private fun updateView() {
         scoreA.text = history.getScoreA().toString()
         scoreB.text = history.getScoreB().toString()
 
@@ -317,7 +322,6 @@ class MainActivity : AppCompatActivity() {
         submit.isEnabled = false
     }
 
-
     private fun chooseThemeDialog() {
 
         val builder = AlertDialog.Builder(this)