Error by including drawable xml-file

Hello community,

I want to iclude different drawable xml-files into my activity_main.xml

However,when I want to includ following code :

  <?xml version="1.0" encoding="utf-8" ?>
<selector xmlns:android="http://ift.tt/nIICcg">
  <item>
    <shape>
      <size
         android:layout_height="110dp" />
    </shape>
  </item>
</selector>

the name is button_height.xml into my main-file:

<Button
                android:id="@+id/cmda1"
                 android:layout_width="110dp"
                android:layout_height="@drawable/button_height" />

It does not work and Eclipse says only:

You must supply a layout_height attribute. and

error in an XML file: aborting build.

I searched an answer in the internet but dont found one. But I think its an easy mistake lots of people are doing.

so, I hope for usefull answers and sorry for my awful english.