app shutsdown on onclick in androidstudio using kotlin - android-studio

Question

am new in kotlin, i am just now making my first code app
there are 2 inputs & 1 button on which i set onclick sum
(i just drag & drop 2 inputs & 1 button, Don't have much knowledge because i have just started kotlin)
Mainactivity.kt
package com.example.hello
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
fun sum (view: View){
var a = number1.toString().toInt()
var b = number2.toString().toInt()
var result = a + b
textView2.text="Result: $result"
}
}
problem is when i click on sum button, my app automatically shuts down
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/number1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:textAlignment="center"
tools:context=".MainActivity"
tools:layout_editor_absoluteX="-82dp"
tools:layout_editor_absoluteY="-24dp">
<Button
android:id="#+id/sum"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="1dp"
android:layout_marginBottom="24dp"
android:hint="+"
android:onClick="sum"
app:layout_constraintBottom_toTopOf="#+id/number2"
app:layout_constraintStart_toStartOf="#+id/number2"
app:layout_constraintTop_toBottomOf="#+id/number1" />
<TextView
android:id="#+id/textView2"
android:layout_width="202dp"
android:layout_height="0dp"
android:layout_marginBottom="281dp"
android:text="TextView"
android:textSize="24sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/number2" />
<EditText
android:id="#+id/number2"
android:layout_width="254dp"
android:layout_height="0dp"
android:layout_marginEnd="61dp"
android:layout_marginBottom="96dp"
android:ems="10"
android:inputType="number"
app:layout_constraintBottom_toTopOf="#+id/textView2"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#+id/sum" />
<EditText
android:id="#+id/number1"
android:layout_width="269dp"
android:layout_height="0dp"
android:layout_marginTop="88dp"
android:layout_marginEnd="46dp"
android:layout_marginBottom="52dp"
android:ems="10"
android:inputType="number"
app:layout_constraintBottom_toTopOf="#+id/sum"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
am getting this error in debugs section:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.hello, PID: 23117
java.lang.IllegalStateException: Could not execute method for android:onClick
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:390)

Answer 1

As the comment said, it's hard to see what is wrong but I guess that number1 and number2 are views/EditTexts? in that case toString won't give you the text of those but instead a description of the object which for example could look like this:
"EditText:{ someinfo, 40183}"
And when you call toInt() on that String, kotlin doesn't know how to convert it and your app crashes.
Instead (if number1 and number2 are edittexts)
try:
number1.getText().toInt()

Answer 2

My guess is it's a NumberFormatException.
Solution:
fun sum (view: View){
var a = number1.text.toString().toInt()
var b = number2.text.toString().toInt()
var result = a + b
textView2.text="Result: $result"
}
You need to call text first to get the actual value in the input View. Calling toString on number1 and number2 will give you the string representation of these objects which is most likely a short description of the object and most likely not a number, hence, the NumberFormatException.