Android: Pendulum Animation

I am working on the splash screen for Monkey Write, and I would like the monkey to be swinging on a vine. In Android you can specify all kinds of animations with xml, so it took me a little bit of time to figure out all the perimeters. Here is my final swinging.xml:

<?xml version="1.0" encoding="utf-8"?>
<rotate xmlns:android="http://schemas.android.com/apk/res/android"
  android:fromDegrees="15"
  android:toDegrees="-15"
  android:pivotX="50%"
  android:pivotY="0%"
  android:duration="2000"
  android:repeatMode="reverse"
  android:repeatCount="-1"
/>

I am using a pivoted rotation to implement the swinging effect. The animation goes from 15 degrees to -15 degrees, but instead of pivoting at the center, I want the pivot point to be at the top-middle. This is achieved by pivotX="50%" and pivotY="0%". For non-stop animation, I use repeatCount="-1".

It was fairly straightforward figure out all those parameters. But the monkey swings from the left to right, then jumps back to the left before swinging again. To make him swing back and forth, I need to set the repeatMode to reverse. Now I have a properly swinging monkey!

I have uploaded my code here: http://github.com/chiuki/android-pendulum-animation. Instead of a monkey, I use xml to specify a pendulum, which seems appropriate for the animation.