Android ZoomableRelativeLayout issue

Question

I'm using this class to add a zoomable relative layout in my application. And my layout is this.

<com.example.zoomablerelativelayoutexample.ZoomableRelativeLayout
    android:layout_width="500dp"
    android:layout_height="500dp"
    android:layout_alignParentTop="true"
    android:background="#000" >

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="124dp"
        android:layout_marginLeft="64dp"
        android:layout_toRightOf="@+id/imageButton1"
        android:src="@drawable/ic_launcher" />

    <ImageButton
        android:id="@+id/imageButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginRight="52dp"
        android:layout_marginTop="131dp"
        android:src="@drawable/ic_launcher" />

</com.example.zoomablerelativelayoutexample.ZoomableRelativeLayout>

Here is the screen shot of the main xml;

Problem is this; when I do the pinch zoom in the RelativeLayout zooms normally. And after making zoom when I move the layout, it moves endless.

I want to limit the move event with the borderline. How can I do it?