ViewPager that wraps current page's height

WrapContentViewPager.java

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

/**
 * {@link ViewPager} that wraps current page's height
 *
 * @author Leo
 */
public class WrapContentViewPager extends ViewPager {
    private Adapter mAdapter;

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

    public WrapContentViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void setAdapter(PagerAdapter adapter) {
        if (!(adapter instanceof Adapter))
            throw new IllegalArgumentException("Adapter of WrapContentViewPager has to implement WrapContentViewPager.Adapter");
        mAdapter = (Adapter) adapter;
        super.setAdapter(adapter);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int height = 0;

        View child = mAdapter == null ? null : mAdapter.getCurrentPageView(getCurrentItem());
        if (child != null) {
            child.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
            int h = child.getMeasuredHeight();
            if (h > height) height = h;
        } else if (getAdapter() != null && getAdapter().getCount() > 0) {
            post(this::requestLayout); // recur until we can get reference to the current page view
        }

        if (height != 0) {
            height += getPaddingTop() + getPaddingBottom(); // take padding into account
            heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
        }

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    public interface Adapter {
        /**
         * <p>Get view for currently selected page of the ViewPager.
         * <p>Since this method is only called to get the View of current page, so implementation of this method should
         * NOT keep references to ALL pages of the ViewPager, but utilize
         * {@link PagerAdapter#destroyItem(ViewGroup, int, Object)} to remove unnecessary references instead.
         * <p>Or you can override {@link PagerAdapter#setPrimaryItem(ViewGroup, int, Object)} to grab reference to
         * current view.
         *
         * @param currentPosition current page of the ViewPager
         * @return {@link View} instance of the current page
         */
        @Nullable
        View getCurrentPageView(int currentPosition);
    }
}