How to add (vertical) divider to a horizontal LinearLayout?

I'm trying to add a divider to a horizontal linear layout but am getting nowhere. The divider just doesn't show. I am a total newbie with Android.

This is my layout XML:

<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" >
    
    <LinearLayout 
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/llTopBar"
        android:orientation="horizontal"
        android:divider="#00ff00"
        android:dividerPadding="22dip"
        android:showDividers="middle">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:text="asdf" />
            
        <Button
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:text="asdf" />
    
    </LinearLayout>
    
</RelativeLayout>

use this for horizontal divider

<View
    android:layout_width="1dp"
    android:layout_height="match_parent"
    android:background="@color/honeycombish_blue" />

and this for vertical divider

<View
    android:layout_width="match_parent"
    android:layout_height="1dp"
    android:background="@color/honeycombish_blue" />

OR if you can use the LinearLayout divider, for horizontal divider

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
    <size android:height="1dp"/>
    <solid android:color="#f6f6f6"/>
</shape>

and in LinearLayout

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:divider="@drawable/divider"
    android:orientation="vertical"
    android:showDividers="middle" >

If you want to user vertical divider then in place of android:height="1dp" in shape use android:width="1dp"

Tip: Don't forget the android:showDividers item.