android VIewpager How to achieve the bound effect

Question

I google the question many days. Find a solution which is add a blank View int the first and end of Viewpager. when viewpager.getcurrentItem()==0,then rePoint to 1. In my

Answer 1

The BounceBackViewPager have a bug, when show mutiple multiple pages(fragment) in one page(screen), only the first page have the OverscrollEffect, that is ,you can see multiple pages on screen, only the first page will bounce back, it looks strange. And only the left side have overscrolleffect, the right side haven't have.

my implement is:

@Override
public float getPageWidth(int position) {
          return    1/mShowPictureSize; 
}

Answer 2

If anyone still wonders how to do this I actually found a solution based on a brilliant library by renard314: https://github.com/inovex/ViewPager3D All the credit should go to him :) Anyways, extends ViewPager:

public class BounceBackViewPager extends ViewPager {

/**
 * maximum z distance to translate child view
 */
final static int DEFAULT_OVERSCROLL_TRANSLATION = 150;

/**
 * duration of overscroll animation in ms
 */
final private static int DEFAULT_OVERSCROLL_ANIMATION_DURATION = 400;

@SuppressWarnings("unused")
private final static String DEBUG_TAG = ViewPager.class.getSimpleName();
private final static int INVALID_POINTER_ID = -1;

/**
 * 
 * @author renard, extended by Piotr Zawadzki
 * 
 */
private class OverscrollEffect {
    private float mOverscroll;
    private Animator mAnimator;

    /**
     * @param deltaDistance [0..1] 0->no overscroll, 1>full overscroll
     */
    public void setPull(final float deltaDistance) {
        mOverscroll = deltaDistance;
        invalidateVisibleChilds(mLastPosition);
    }

    /**
     * called when finger is released. starts to animate back to default position
     */
    private void onRelease() {
        if (mAnimator != null && mAnimator.isRunning()) {
            mAnimator.addListener(new AnimatorListener() {

                @Override
                public void onAnimationStart(Animator animation) {
                }

                @Override
                public void onAnimationRepeat(Animator animation) {
                }

                @Override
                public void onAnimationEnd(Animator animation) {
                    startAnimation(0);
                }

                @Override
                public void onAnimationCancel(Animator animation) {
                }
            });
            mAnimator.cancel();
        } else {
            startAnimation(0);
        }
    }

    private void startAnimation(final float target) {
        mAnimator = ObjectAnimator.ofFloat(this, "pull", mOverscroll, target);
        mAnimator.setInterpolator(new DecelerateInterpolator());
        final float scale = Math.abs(target - mOverscroll);
        mAnimator.setDuration((long) (mOverscrollAnimationDuration * scale));
        mAnimator.start();
    }

    private boolean isOverscrolling() {
        if (mScrollPosition == 0 && mOverscroll < 0) {
            return true;
        }
        final boolean isLast = (getAdapter().getCount() - 1) == mScrollPosition;
        if (isLast && mOverscroll > 0) {
            return true;
        }
        return false;
    }

}

final private OverscrollEffect mOverscrollEffect = new OverscrollEffect();
final private Camera mCamera = new Camera();

private OnPageChangeListener mScrollListener;
private float mLastMotionX;
private int mActivePointerId;
private int mScrollPosition;
private float mScrollPositionOffset;
final private int mTouchSlop;

private float mOverscrollTranslation;
private int mOverscrollAnimationDuration;

public BounceBackViewPager(Context context, AttributeSet attrs) {
    super(context, attrs);
    setStaticTransformationsEnabled(true);
    final ViewConfiguration configuration = ViewConfiguration.get(context);
    mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
    super.setOnPageChangeListener(new MyOnPageChangeListener());
    init(attrs);
}

private void init(AttributeSet attrs) {
    TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.BounceBackViewPager);
    mOverscrollTranslation = a.getDimension(R.styleable.BounceBackViewPager_overscroll_translation, DEFAULT_OVERSCROLL_TRANSLATION);
    mOverscrollAnimationDuration = a.getInt(R.styleable.BounceBackViewPager_overscroll_animation_duration, DEFAULT_OVERSCROLL_ANIMATION_DURATION);
    a.recycle();
}

public int getOverscrollAnimationDuration() {
    return mOverscrollAnimationDuration;
}

public void setOverscrollAnimationDuration(int mOverscrollAnimationDuration) {
    this.mOverscrollAnimationDuration = mOverscrollAnimationDuration;
}

public float getOverscrollTranslation() {
    return mOverscrollTranslation;
}

public void setOverscrollTranslation(int mOverscrollTranslation) {
    this.mOverscrollTranslation = mOverscrollTranslation;
}

@Override
public void setOnPageChangeListener(OnPageChangeListener listener) {
    mScrollListener = listener;
};

private void invalidateVisibleChilds(final int position) {
     for (int i = 0; i < getChildCount(); i++) {
     getChildAt(i).invalidate();

     }
    //this.invalidate();
    // final View child = getChildAt(position);
    // final View previous = getChildAt(position - 1);
    // final View next = getChildAt(position + 1);
    // if (child != null) {
    // child.invalidate();
    // }
    // if (previous != null) {
    // previous.invalidate();
    // }
    // if (next != null) {
    // next.invalidate();
    // }
}

private int mLastPosition = 0;

private class MyOnPageChangeListener implements OnPageChangeListener {

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        if (mScrollListener != null) {
            mScrollListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
        }
        mScrollPosition = position;
        mScrollPositionOffset = positionOffset;
        mLastPosition = position;
        invalidateVisibleChilds(position);
    }

    @Override
    public void onPageSelected(int position) {

        if (mScrollListener != null) {
            mScrollListener.onPageSelected(position);
        }
    }

    @Override
    public void onPageScrollStateChanged(final int state) {

        if (mScrollListener != null) {
            mScrollListener.onPageScrollStateChanged(state);
        }
        if (state == SCROLL_STATE_IDLE) {
            mScrollPositionOffset = 0;
        }
    }
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    try {
        final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;
        switch (action) {
        case MotionEvent.ACTION_DOWN: {
            mLastMotionX = ev.getX();
            mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
            break;
        }
        case MotionEventCompat.ACTION_POINTER_DOWN: {
            final int index = MotionEventCompat.getActionIndex(ev);
            final float x = MotionEventCompat.getX(ev, index);
            mLastMotionX = x;
            mActivePointerId = MotionEventCompat.getPointerId(ev, index);
            break;
        }
        }
        return super.onInterceptTouchEvent(ev);
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
        return false;
    } catch (ArrayIndexOutOfBoundsException e) {
        e.printStackTrace();
        return false;
    }
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    try {
        return super.dispatchTouchEvent(ev);
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
        return false;
    } catch (ArrayIndexOutOfBoundsException e) {
        e.printStackTrace();
        return false;
    }
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    boolean callSuper = false;

    final int action = ev.getAction();
    switch (action) {
    case MotionEvent.ACTION_DOWN: {
        callSuper = true;
        mLastMotionX = ev.getX();
        mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
        break;
    }
    case MotionEventCompat.ACTION_POINTER_DOWN: {
        callSuper = true;
        final int index = MotionEventCompat.getActionIndex(ev);
        final float x = MotionEventCompat.getX(ev, index);
        mLastMotionX = x;
        mActivePointerId = MotionEventCompat.getPointerId(ev, index);
        break;
    }
    case MotionEvent.ACTION_MOVE: {
        if (mActivePointerId != INVALID_POINTER_ID) {
            // Scroll to follow the motion event
            final int activePointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
            final float x = MotionEventCompat.getX(ev, activePointerIndex);
            final float deltaX = mLastMotionX - x;
            final float oldScrollX = getScrollX();
            final int width = getWidth();
            final int widthWithMargin = width + getPageMargin();
            final int lastItemIndex = getAdapter().getCount() - 1;
            final int currentItemIndex = getCurrentItem();
            final float leftBound = Math.max(0, (currentItemIndex - 1) * widthWithMargin);
            final float rightBound = Math.min(currentItemIndex + 1, lastItemIndex) * widthWithMargin;
            final float scrollX = oldScrollX + deltaX;
            if (mScrollPositionOffset == 0) {
                if (scrollX < leftBound) {
                    if (leftBound == 0) {
                        final float over = deltaX + mTouchSlop;
                        mOverscrollEffect.setPull(over / width);
                    }
                } else if (scrollX > rightBound) {
                    if (rightBound == lastItemIndex * widthWithMargin) {
                        final float over = scrollX - rightBound - mTouchSlop;
                        mOverscrollEffect.setPull(over / width);
                    }
                }
            } else {
                mLastMotionX = x;
            }
        } else {
            mOverscrollEffect.onRelease();
        }
        break;
    }
    case MotionEvent.ACTION_UP:
    case MotionEvent.ACTION_CANCEL: {
        callSuper = true;
        mActivePointerId = INVALID_POINTER_ID;
        mOverscrollEffect.onRelease();
        break;
    }
    case MotionEvent.ACTION_POINTER_UP: {
        final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
        final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose a new
            // active pointer and adjust accordingly.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mLastMotionX = ev.getX(newPointerIndex);
            mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
            callSuper = true;
        }
        break;
    }
    }

    if (mOverscrollEffect.isOverscrolling() && !callSuper) {
        return true;
    } else {
        return super.onTouchEvent(ev);
    }
}

@Override
protected boolean getChildStaticTransformation(View child, Transformation t) {
    if (child.getWidth() == 0) {
        return false;
    }
    final int position = child.getLeft() / child.getWidth();
    final boolean isFirstOrLast = position == 0 || (position == getAdapter().getCount() - 1);
    if (mOverscrollEffect.isOverscrolling() && isFirstOrLast) {
        final float dx = getWidth() / 2;
        final int dy = getHeight() / 2;
        t.getMatrix().reset();
        final float translateX =(float) mOverscrollTranslation * (mOverscrollEffect.mOverscroll > 0 ? Math.min(mOverscrollEffect.mOverscroll, 1) : Math.max(mOverscrollEffect.mOverscroll, -1));
        mCamera.save();
        mCamera.translate(-translateX, 0, 0);
        mCamera.getMatrix(t.getMatrix());
        mCamera.restore();
        t.getMatrix().preTranslate(-dx, -dy);
        t.getMatrix().postTranslate(dx, dy);

        if (getChildCount() == 1) {
            this.invalidate();
        } else {
            child.invalidate();
        }
        return true;
    }
    return false;
}

}

and add a resources file somewhere in the values folder:

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="BounceBackViewPager">
    <!--
    determines the maximum amount of translation along the z-axis during the overscroll. 
    Default is 150.
    -->
    <attr name="overscroll_translation" format="dimension" />

    <!-- Duration of animation when user releases the over scroll. Default is 400 ms. -->
    <attr name="overscroll_animation_duration" format="integer" />
</declare-styleable>

All I had to do was to change the transformation to support translateX. I strongly recommend reading the documentation for ViewPager3D first.