How to know viewpager is scroll left or right?

Question

I am using ViewPager (support library). I want to know every time the ViewPager change the visible page, it is scrolling left or right.

Please give me a solution. An

Answer 1

It's not a perfect solution but here's a way to check the swipe direction when you start swiping:

new ViewPager.OnPageChangeListener() {

            private static final float thresholdOffset = 0.5f;
            private boolean scrollStarted, checkDirection;

            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                if (checkDirection) {
                    if (thresholdOffset > positionOffset) {
                        Log.i(C.TAG, "going left");
                    } else {
                        Log.i(C.TAG, "going right");
                    }
                    checkDirection = false;
                }
            }

            @Override
            public void onPageSelected(int position) {}

            @Override
            public void onPageScrollStateChanged(int state) {
                if (!scrollStarted && state == ViewPager.SCROLL_STATE_DRAGGING) {
                    scrollStarted = true;
                    checkDirection = true;
                } else {
                    scrollStarted = false;
                }
            }
        });

EDIT: there's a more elegant approach that involves using a ViewPager.PageTransformer and checking it's position intervals:

...
myViewPager.setPageTransformer(true, new PageTransformer());
...

public class PageTransformer implements ViewPager.PageTransformer {
    public void transformPage(View view, float position) {

        if (position < -1) { 
            // [-00,-1): the page is way off-screen to the left.
        } else if (position <= 1) { 
            // [-1,1]: the page is "centered"
        } else { 
            // (1,+00]: the page is way off-screen to the right.           
        }
    }
}

You can learn more from: Using ViewPager for Screen Slides

Answer 2

use that

@Override
public void onPageSelected( int position )
{
    mCurrentFragmentPosition = position;
}
@Override
public void onPageScrolled( int position, float positionOffset, int positionOffsetPixels )
{
    boolean isGoingToRightPage = position == mCurrentFragmentPosition;
    if(isGoingToRightPage)
    {
        // user is going to the right page
    }
    else
    {
        // user is going to the left page
    }
}

Answer 3

set setOnPageChangeListener to your ViewPager

keep a variable global as

private int lastPosition = 0;

and in

@Override
public void onPageSelected(int arg0) {
    if (lastPosition > position) {
         System.out.println("Left");
      }else if (lastPosition < position) {
         System.out.println("Right");
      }
      lastPosition = position;
}

Answer 4

You can keep class member variable to save last visited page

private int mLastVisitedPageIndex = 0;

Then use following function to check direction

@Override
public void onPageSelected(int i) {
    boolean isMovingForward = mLastVisitedPageIndex < i?true:false;
    //Use isMovingForward variable anywhere now
    mLastVisitedPageIndex = i;
}

Answer 5

private float sumPositionAndPositionOffset;

@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    boolean isSwipeToLeft = position + positionOffset > sumPositionAndPositionOffset;
    sumPositionAndPositionOffset = position + positionOffset;   
}

Answer 6

Apologies - had to edit the answer as I found a bug. Here is improved solution:

The solution compares current page index with one previously selected (previousPageIndex)

newPageIndex represents the page which is about to be scrolled to.

Condition (positionOffset == 0) compares if the scroll finished

private int previousPageIndex = 0;
private int newPageIndex = -1;

private final int MOVE_DIRECTION_NONE = 0;
private final int MOVE_DIRECTION_LEFT = 1;
private final int MOVE_DIRECTION_RIGHT = 2;

private int moveDirection = MOVE_DIRECTION_NONE;


@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    super.onPageScrolled(position, positionOffset, positionOffsetPixels);

    if (moveDirection == MOVE_DIRECTION_NONE) {
        if (previousPageIndex  == position){
            moveDirection = MOVE_DIRECTION_LEFT;
            if (newPageIndex == -1) newPageIndex = previousPageIndex + 1;
        }  else {
            moveDirection = MOVE_DIRECTION_RIGHT;
            if (newPageIndex == -1) newPageIndex = previousPageIndex - 1;
        }
    }

    if (positionOffset == 0) {
        System.out.println("Reseting");
        previousPageIndex = position;
        moveDirection = MOVE_DIRECTION_NONE;
        newPageIndex = -1;
    }

    switch (moveDirection) {
        case MOVE_DIRECTION_LEFT:
            if (onPageChangingHandler != null) onPageChangingHandler.pageChanging(previousPageIndex, newPageIndex, positionOffset);
            System.out.println("Sliding Left | Previous index: " + previousPageIndex + " | New Index: " + newPageIndex + " | offset: " + positionOffset  + " | Position: " + position);
            break;
        case MOVE_DIRECTION_RIGHT:
            if (onPageChangingHandler != null) onPageChangingHandler.pageChanging(newPageIndex, previousPageIndex, positionOffset);
            System.out.println("Sliding Right | Previous index: " + previousPageIndex + " | New Index: " + newPageIndex + " | offset: " + positionOffset + " | Position: " + position);
            break;
        case MOVE_DIRECTION_NONE:
            System.out.println("Moving NONE");
            break;
    }
}