PageIndicatorView.java

package org.nevack.nevedomskymobdev.welcome;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;

public class PageIndicatorView extends View{

    private int currentPage = 2;
    private int pageCount = 5;

    private Paint active;
    private Paint inactive;

    private int radius;
    private int pad;
    private int width= 200;
    private int height = 40;

    public PageIndicatorView(Context context) {
        super(context);
        init();
    }

    public PageIndicatorView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public PageIndicatorView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        radius = 20;
        pad = radius * 2;

        width = (pad * (pageCount - 1)) + (radius * 2 * pageCount);
        height = pad;

        // Try for a width based on our minimum
        int minw = getPaddingLeft() + getPaddingRight() + width;
        int w = resolveSizeAndState(minw, widthMeasureSpec, 0);

        // Whatever the width ends up being, ask for a height that would let the pie
        // get as big as it can
        int minh = getPaddingBottom() + getPaddingTop() + height;
        int h = resolveSizeAndState(minh, heightMeasureSpec, 0);

        setMeasuredDimension(w, h);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        for (int i = 0; i < pageCount; i++) {
            canvas.drawCircle(
                    (canvas.getWidth() - width) / 2 + pad * i + radius * 2 * i + radius,
                    canvas.getHeight() / 2,
                    radius,
                    inactive
            );
        }

        int x = currentPage - 1;
        canvas.drawCircle(
                (canvas.getWidth() - width) / 2 + pad * x + radius * 2 * x + radius,
                canvas.getHeight() / 2,
                radius,
                active
        );
    }

    private void init() {
        active = new Paint(Paint.ANTI_ALIAS_FLAG);
        active.setColor(Color.DKGRAY);

        inactive = new Paint(Paint.ANTI_ALIAS_FLAG);
        inactive.setColor(Color.GRAY);
    }

    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
        invalidate();
    }

    public void setPageCount(int pageCount) {
        this.pageCount = pageCount;
        invalidate();
        requestLayout();
    }
}