Code example for DataSetObservable

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 * set change may involve pages being added, removed, or changing position. The 
 * ViewPager will keep the current page active provided the adapter implements 
 * the method {@link #getItemPosition(Object)}.</p> 
 */ 
public abstract class AwfulPagerAdapter { 
    private DataSetObservable mObservable = new DataSetObservable();
 
    public static final int POSITION_UNCHANGED = -1;
    public static final int POSITION_NONE = -2;
 
    /** 
     * Return the number of views available. 
     */ 
    public abstract int getCount(); 
 
    /** 
     * Called when a change in the shown pages is going to start being made. 
     * @param container The containing View which is displaying this adapter's 
     * page views. 
     */ 
    public void startUpdate(ViewGroup container) {