Animate image with ImageView

I am get an exception when I try to animate an image through frame and ImageView. Here is the code:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    ImageView rocketImage = (ImageView) findViewById(R.id.imageView1);
    rocketImage.setBackgroundResource(R.drawable.animation_sample);
    AnimationDrawable rocketAnimation = (AnimationDrawable) rocketImage.getBackground();
    rocketAnimati开发者_JS百科on.run();
}

and my animation_sample.xml

<frames id="anim_sample" oneshot="false">
  <frame drawable="@drawable/a1" duration="50" />
  <frame drawable="@drawable/a2" duration="50" />
  <frame drawable="@drawable/a3" duration="50" />  
  <frame drawable="@drawable/a4" duration="50" />
  <frame drawable="@drawable/a5" duration="50" />
</frames>

and main.xml

<?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="fill_parent">
    <ImageView android:id="@+id/imageView1" android:src="@drawable/icon"
        android:layout_width="wrap_content" android:layout_height="wrap_content"></ImageView>
</LinearLayout>

Am I missing anything (in manifest.xml or any other)?

try with this animation_sample.xml

<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/anim_sample" android:oneshot="false">
  <item android:drawable="@drawable/a1" android:duration="50" />
  <item android:drawable="@drawable/a2" android:duration="50" />
  <item android:drawable="@drawable/a3" android:duration="50" />  
  <item android:drawable="@drawable/a4" android:duration="50" />
  <item android:drawable="@drawable/a5" android:duration="50" />
</animation-list>

sorry if there are some errors but I don't have here eclipse and the SDK