how to identify input from keyboard that is number or not and then change UI according that ,, reference taken from phonepe

 1- Xml Code 

<?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:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginStart="10dp"
    android:layout_marginTop="10dp"
    android:layout_marginEnd="10dp"
    tools:context=".TryToggle">

    <EditText
        android:id="@+id/etEntNumber"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:layout_marginEnd="10dp"
        android:hint="Enter NUmber"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnVisibal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="15dp"
        android:gravity="center"
        android:text="Working"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/etEntNumber" />

</androidx.constraintlayout.widget.ConstraintLayout>

2-Logic for Identify user input is Number or not and show different different design according to user input:

switchOnOff.addTextChangedListener ( object : TextWatcher{
    override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {

    }

    override fun onTextChanged(userInput: CharSequence?, p1: Int, p2: Int, p3: Int) {
    val inputText = userInput.toString().trim()
        if (!inputText.isNullOrEmpty()){
            if (isNumeric(inputText)){
                btnVisibal.visibility= View.VISIBLE
            }else{
                btnVisibal.visibility= View.GONE
            }
        }

    }

    override fun afterTextChanged(p0: Editable?) {

    }
})

fun isNumeric(str: String): Boolean {
    return str.toDoubleOrNull() != null
}