How do you add Button inside the RelativeLayout?

Make sure you're in the .xml file under Layout, not under Menu. You can either use the design editor to drag in a button, or create one yourself directly in the xml code. Here's an example:

<Button
    android:id="@+id/loginButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="20dp" />

You can copy and paste that into the xml file in between the RelativeLayout header and </RelativeLayout>.and a button will be created, then you can modify it to suit your needs.

Hi Seyfullah,

All you need to create a button is this syntax within Relative Layout ---- <Button*/>* and is completely valid.

However, adding additional attributes to the button like id, size etc. you can rely on Brahm's answer.

<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"
    tools:context=".MainActivity" >

    // This is where you create the button (inbetween the opening and closing Relative Layout tags)

</RelativeLayout>

Hope this helps