A simple ViewPagerIndicator that shows an 'on' or 'off' image per page appropriately

OnOffPageIndicator.java

package nl.nl2312.android.components;

import nl.nl2312.android.R;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.drawable.Drawable;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;

import com.viewpagerindicator.PageIndicator;

public class OnOffPageIndicator extends LinearLayout implements PageIndicator {

	private static final float INDICATOR_MARGIN = 3F; // In dip
	
	private final Drawable offDrawable;
	private final Drawable onDrawable;
	private ViewPager viewPager;
	private int currentPage;
	private final int indicatorMargin;
	private final float screenScale = getResources().getDisplayMetrics().density;

	public OnOffPageIndicator(Context context) {
		this(context, null);
	}

	public OnOffPageIndicator(Context context, AttributeSet attrs) {
		this(context, attrs, 0);
	}

	public OnOffPageIndicator(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);

		final Resources res = getResources();
		offDrawable = res.getDrawable(R.drawable.widget_indicator_off);
		onDrawable = res.getDrawable(R.drawable.widget_indicator_on);
		indicatorMargin = (int) (INDICATOR_MARGIN * screenScale + 0.5f);

	}

	@Override
	public void setViewPager(ViewPager view) {
		if (viewPager == view) {
			return;
		}
		if (viewPager != null) {
			viewPager.setOnPageChangeListener(null);
		}
		if (view.getAdapter() == null) {
			throw new IllegalStateException("ViewPager does not have adapter instance.");
		}
		viewPager = view;
		viewPager.setOnPageChangeListener(this);
		buildIndicator();
	}

	private void buildIndicator() {
		removeAllViews();
		for (int i = 0; i < viewPager.getAdapter().getCount(); i++) {
			ImageView circle = new ImageView(getContext());
			circle.setImageDrawable(offDrawable);
			MarginLayoutParams mlp = new ViewGroup.MarginLayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
					ViewGroup.LayoutParams.WRAP_CONTENT);
			//mlp.setMargins(indicatorMargin, 0, indicatorMargin, 0);
			circle.setPadding(indicatorMargin, 0, indicatorMargin, 0);
			addView(circle, mlp);
		}
	}

	@Override
	public void setCurrentItem(int item) {
		if (viewPager == null) {
			throw new IllegalStateException("ViewPager has not been bound.");
		}
		viewPager.setCurrentItem(item);
		currentPage = item;
		updateIndicator();
	}

	private void updateIndicator() {
		for (int i = 0; i < viewPager.getAdapter().getCount(); i++) {
			ImageView circle = (ImageView) getChildAt(i);
			circle.setImageDrawable(i == currentPage? onDrawable: offDrawable);
		}
	}

	@Override
	public void setViewPager(ViewPager view, int initialPosition) {
		setViewPager(view);
		setCurrentItem(initialPosition);
	}

	@Override
	public void notifyDataSetChanged() {
	}

	@Override
	public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
	}

	@Override
	public void onPageSelected(int position) {
		currentPage = position;
		updateIndicator();
	}

	@Override
	public void setOnPageChangeListener(ViewPager.OnPageChangeListener listener) {
	}

	@Override
	public void onPageScrollStateChanged(int arg0) {
	}

}