Reflection with ViewPager

I've done a VerticalViewPager by extending the android.support.v4.view.ViewPager class..

Now I am trying to reflect a field of the class. My goal is to change the sensitivity of the scrolling effect of the (Vertical)ViewPager. Netherless nothings changes, it doesn't seem to have any effect on the fields of the super class. I already tried to change other fields such as "DEBUG" but there isn't any change right now. I can't understand why.

Thanks for any help in advance.

. . . . . . . . . . .

This is the reflection code right now:

Field mFlingDistance;
        mFlingDistance = ViewPager.class.getDeclaredField("mFlingDistance");
        mFlingDistance.setAccessible(true);

        // Set custom value:
        mFlingDistance.set(this, 20);

Whole VerticalViewPager Class:

package de.XXX.app.Activitys.fragments;

import android.content.Context;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

public class VerticalViewPager extends ViewPager {
    public VerticalViewPager(Context context) {
        super(context);
        init();
    }

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

    private void init() {

        try {
            Field mFlingDistance;
            mFlingDistance = ViewPager.class.getDeclaredField("mFlingDistance");
            mFlingDistance.setAccessible(true);

            // Set custom value:
            mFlingDistance.set(this, 20);
        }catch (Exception e){
            System.out.println("SMTH Happend!:(");
        }

        setPageTransformer(true, new VerticalPageTransformer());
        setOverScrollMode(OVER_SCROLL_NEVER);
    }

    private class VerticalPageTransformer implements ViewPager.PageTransformer {

        @Override
        public void transformPage(View view, float position) {

            if (position < -1) {
                view.setAlpha(0);
            } else if ( position <= 1) {
                view.setAlpha(1);

                view.setTranslationX(view.getWidth() * -position);

                float yPosition = position * (view.getHeight()/(1/0.6f));
                view.setTranslationY(yPosition);
            } else {
                view.setAlpha(0);
            }
        }
    }

    private MotionEvent swapXY(MotionEvent ev) {
        float width = getWidth();
        float height = getHeight();

        float newX = (ev.getY() / height) * width;
        float newY = (ev.getX() / width) * height;

        ev.setLocation(newX, newY);

        return ev;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        boolean intercepted = super.onInterceptTouchEvent(swapXY(ev));
        swapXY(ev);
        return intercepted;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        return super.onTouchEvent(swapXY(ev));
    }


    private static void setFinalStaticField(Class<?> clazz, String fieldName, Object value)
            throws ReflectiveOperationException {
        Field field = clazz.getDeclaredField(fieldName);
        field.setAccessible(true);
        Field modifiers = Field.class.getDeclaredField("modifiers");
        modifiers.setAccessible(true);
        modifiers.setInt(field, field.getModifiers() & ~Modifier.FINAL);
        field.set(null, value);
    }

}