xml code simple calculator

calculator.xml

<?xml version="1.0" encoding="utf-8"?>


<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <EditText
        android:layout_height="wrap_content"
    android:inputType="number"
    android:ems="10"
    android:id="@+id/etFirstNumber"
        android:layout_width="wrap_content"
        android:hint="first number"
        android:layout_marginStart="23dp"
        android:layout_marginTop="50dp"
        android:textColor="@color/colorAccent"
        android:layout_below="@+id/tvHeader"
        android:layout_alignParentStart="true"
        android:textSize="25sp" />

    <EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="number"
    android:ems="10"
    android:id="@+id/etSecondNumber"
        android:textColor="@color/colorAccent"
        android:layout_below="@+id/etFirstNumber"
        android:layout_alignStart="@+id/etFirstNumber"
        android:layout_marginTop="43dp"
        android:hint="second number"
        android:textSize="25sp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="CALCULATOR"
        android:id="@+id/tvHeader"
        android:textColor="@color/colorAccent"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="26dp" />

    <TextView
        android:layout_width="229dp"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:id="@+id/tvResult"
        android:textColor="@color/colorAccent"
        android:layout_marginBottom="60dp"
        android:hint="the result"
        android:layout_weight="1"
        android:textAlignment="textStart"
        android:textSize="30sp"
        android:layout_alignParentBottom="true"
        android:layout_alignEnd="@+id/etSecondNumber"
        android:textStyle="normal|italic" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="/"
        android:id="@+id/btnDivide"
        android:background="@color/colorAccent"
        android:onClick="onClick (MainActivity)"
        android:layout_marginLeft="3dp"
        android:layout_marginRight="0dp"
        android:layout_alignBaseline="@+id/btnMultiply"
        android:layout_alignBottom="@+id/btnMultiply"
        android:layout_alignParentEnd="true"
        android:textSize="20sp"
        android:textColor="@android:color/background_light"
        android:elevation="10dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"
        android:id="@+id/btnAdd"
        android:background="@color/colorAccent"
        android:onClick="onClick (MainActivity)"
        android:padding="5dp"
        android:paddingRight="5dp"
        android:paddingLeft="5dp"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="3dp"
        android:layout_marginTop="32dp"
        android:layout_below="@+id/etSecondNumber"
        android:layout_alignParentStart="true"
        android:autoText="true"
        android:textSize="20sp"
        android:textColor="@android:color/background_light"
        android:elevation="24dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-"
        android:id="@+id/btnSubtract"
        android:background="@color/colorAccent"
        android:onClick="onClick (MainActivity)"
        android:paddingLeft="3dp"
        android:paddingRight="3dp"
        android:layout_marginLeft="3dp"
        android:layout_marginRight="3dp"
        android:layout_alignBaseline="@+id/btnAdd"
        android:layout_alignBottom="@+id/btnAdd"
        android:layout_alignStart="@+id/tvResult"
        android:layout_toStartOf="@+id/btnMultiply"
        android:textSize="20sp"
        android:textColor="@android:color/background_light"
        android:elevation="9dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="*"
        android:id="@+id/btnMultiply"
        android:background="@color/colorAccent"
        android:onClick="onClick (MainActivity)"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="3dp"
        android:layout_alignTop="@+id/btnSubtract"
        android:layout_toStartOf="@+id/btnDivide"
        android:textSize="20sp"
        android:textColor="@android:color/background_light"
        android:elevation="9dp" />

</RelativeLayout>