How to get rid of the extra gap between a button and other views?

Question

When I created a button view, Android always create some extra space between this button and other views below it.

In this example below, there is a button above the second button. You can see the gap between these two buttons. How can I get rid of this gap? Thanks.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="wrap_content">

    <Button android:id="@+id/up"
        android:layout_width="fill_parent" android:layout_height="28dip"
        android:textSize="9sp" android:gravity="center" android:text="Hide sth"
        android:layout_marginBottom="0" android:paddingBottom="0" />
    <Button android:id="@+id/down"
        android:layout_width="fill_parent" android:layout_height="28dip"
        android:textSize="9sp" android:gravity="center" android:text="Show sth" />
   </LinearLayout>

Answer 1

Create your own button background nine-patch PNG that eliminates the space. You can find the existing background files in your SDK.

Answer 2

CommonsWare pretty much pointed you in the right direction but here's a sample layout example. Just replace the android:background="COLOR" to a reference of a 9 patch png

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="wrap_content">

<Button
    android:id="@+id/btn1"
    android:text="btn1"
    android:padding="0dip"
    android:layout_margin="0dip"
    android:layout_width="fill_parent"
    android:layout_height="40dip"
    android:background="#FFF"
/>

<Button
    android:id="@+id/btn2"
    android:text="btn2"
    android:padding="0dip"
    android:layout_margin="0dip"
    android:layout_width="fill_parent"
    android:layout_height="40dip"
    android:background="#FF0000"
/>


</LinearLayout>

Hope that helps!