ViewPager listener to change colors on swiping

ColorChangeEvaluatorListener.java

package com.corewillsoft.loansdeposits.ui.utils;

import android.animation.ArgbEvaluator;
import android.os.Handler;
import android.support.v4.view.ViewPager;

import static android.support.v4.view.ViewPager.SCROLL_STATE_IDLE;
import static com.corewillsoft.loansdeposits.ui.utils.SwipeDirectionDetector.Direction.LEFT;
import static com.corewillsoft.loansdeposits.ui.utils.SwipeDirectionDetector.Direction.RIGHT;

public abstract class ColorChangeEvaluatorListener implements ViewPager.OnPageChangeListener {

    private final SwipeDirectionDetector directionDetector;
    private final ArgbEvaluator evaluator;
    private final int[] colors;
    private int currentItem;
    private ViewPager viewPager;
    private float prevOffset;
    private Handler handler = new Handler();

    public ColorChangeEvaluatorListener(ViewPager viewPager, int[] colors) {
        this.viewPager = viewPager;
        handler.post(() -> {
            currentItem = viewPager.getCurrentItem();
            updateColor();
        });
        currentItem = viewPager.getCurrentItem();
        evaluator = new ArgbEvaluator();
        directionDetector = new SwipeDirectionDetector();
        this.colors = colors;
        updateColor();
    }

    @Override
    public void onPageScrolled(int position, float offset, int positionOffsetPixels) {
        directionDetector.onPageScrolled(position, offset, positionOffsetPixels);
        if (Math.abs(prevOffset - offset) > 0.3) {
            currentItem = viewPager.getCurrentItem();
        }
        prevOffset = offset;

        if (offset > 0) {
            updateColor(offset);
        }
    }

    @Override
    public void onPageSelected(int position) {
        directionDetector.onPageSelected(position);
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        directionDetector.onPageScrollStateChanged(state);
        if (state == SCROLL_STATE_IDLE) {
            currentItem = viewPager.getCurrentItem();
            updateColor();
        }
    }

    private void updateColor(float offset) {
        int currentColor = colors[currentItem];

        int position = currentItem;
        if (directionDetector.getDirection() == RIGHT) {
            position = currentItem + 1;
        } else if (directionDetector.getDirection() == LEFT) {
            position = currentItem - 1;
            offset = 1 - offset;
        }
        position = Math.max(0, position);
        position = Math.min(colors.length - 1, position);
        int nextColor = colors[position];
        colorChanged((Integer) evaluator.evaluate(offset, currentColor, nextColor));
    }

    private void updateColor() {
        handler.post(() -> colorChanged(colors[currentItem]));
    }

    public abstract void colorChanged(int color);
}

SwipeDirectionDetector.java

package com.corewillsoft.loansdeposits.ui.utils;

import android.support.v4.view.ViewPager;

import static com.corewillsoft.loansdeposits.ui.utils.SwipeDirectionDetector.Direction.LEFT;
import static com.corewillsoft.loansdeposits.ui.utils.SwipeDirectionDetector.Direction.NO_DIRECTION;
import static com.corewillsoft.loansdeposits.ui.utils.SwipeDirectionDetector.Direction.RIGHT;

public class SwipeDirectionDetector implements ViewPager.OnPageChangeListener {
    private Direction direction;
    private int lastState;

    public enum Direction {
        LEFT,
        RIGHT,
        NO_DIRECTION
    }

    @Override
    public void onPageScrolled(int position, float offset, int positionOffsetPixels) {
        boolean leftStarted = direction == LEFT && offset > 0.5;
        boolean rightStarted = direction == RIGHT && offset < 0.5;
        if (lastState == ViewPager.SCROLL_STATE_DRAGGING && (leftStarted || rightStarted)) {
            direction = NO_DIRECTION;
        }
        initDirection(offset);
    }

    @Override
    public void onPageSelected(int position) {

    }

    @Override
    public void onPageScrollStateChanged(int state) {
        lastState = state;
    }

    private void initDirection(float offset) {
        if (direction == NO_DIRECTION && offset > 0) {
            if (offset > 0.5) {
                direction = LEFT;
            } else {
                direction = RIGHT;
            }
        }
        if (offset == 0) {
            direction = NO_DIRECTION;
        }
    }

    public Direction getDirection() {
        return direction;
    }
}