Relative layout within Relative layout

Question

This is the code of my activity.xml here I used two relative layout but it is not accepting the id's of the txt views within which is why i am not able to use them in my java code. I don't know what the problem is.

 
<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <com.example.gproject.GameView
        android:id="@+id/gv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
    <TextView
        android:visibility="invisible"
        android:id="@+id/txt_score"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#002247"
        android:textSize="50sp"
        android:text="0"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"/>
    <Button
        android:id="@+id/btn_start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start"
        android:padding="5dp"
        android:layout_centerInParent="true"
        android:background="#ffffff"
        android:textColor="#000000"
        />
    <RelativeLayout
        android:id="@+id/r1_game_over"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="invisible">
        <TextView
            android:id="@+id/txt_game_over"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Game Over"
            android:textSize="50sp"
            android:layout_centerInParent="true"
            android:textColor="#ff00"/>

    </RelativeLayout>
</RelativeLayout>