There is no error in your java code. Its perfect you have just change your xml. Use this.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/RelativeLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FFFFFF"
tools:context=".AddFriendsCustomActivity" >
<EditText
android:id="@+id/writename"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="24dp"
android:ems="10" >
<requestFocus />
</EditText>
<ImageView
android:id="@+id/add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@+id/writename"
android:layout_marginLeft="20dp"
android:layout_toRightOf="@+id/writename"
android:contentDescription="Add Friend"
android:src="@drawable/ic_launcher" />
<Button
android:id="@+id/submit_dialog"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="@+id/writename"
android:layout_below="@+id/add"
android:layout_marginRight="46dp"
android:text="Submit" />
</RelativeLayout>