Android Viewpager 跳到半页 [英] Android Viewpager bounce to half a page

问题描述

所以我想要实现的是用户将打开到视图寻呼机的第一页，而视图寻呼机将弹回第二页的一半并弹回第一页，表明还有更多页面要滚动到.我想知道如何实现这一点?

So what i am trying to achieve is user would open to first page of the view pager, and the view pager would bounce to half of the second page and bounce back to the fist page indicating that there are more pages to scroll to. I was wondering on how i could implement this?

推荐答案

你可以使用 fakeDragBy 方法来实现这个效果:

You can use fakeDragBy method to achieve this effect:

viewPager.beginFakeDrag();
viewPager.fakeDragBy(offset); //offset in pixels. 
viewPager.endFakeDrag();

我已经为此制定了方法:

I have made method for this:

private int animFactor;
private ValueAnimator animator = new ValueAnimator();

private void animateViewPager(final ViewPager pager, final int offset, final int delay) {
    if (!animator.isRunning()) {
        animator.removeAllUpdateListeners();
        animator.removeAllListeners();
        //Set animation
        animator.setIntValues(0, -offset);
        animator.setDuration(delay);
        animator.setRepeatCount(1);
        animator.setRepeatMode(ValueAnimator.RESTART);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            public void onAnimationUpdate(ValueAnimator animation) {
                Integer value = animFactor * (Integer) animation.getAnimatedValue();
                if (!pager.isFakeDragging()) {
                    pager.beginFakeDrag();
                }
                pager.fakeDragBy(value);
            }
        });
        animator.addListener(new AnimatorListenerAdapter() {

            @Override
            public void onAnimationStart(Animator animation) {
                animFactor = 1;
            }

            @Override
            public void onAnimationEnd(Animator animation) {
                pager.endFakeDrag();
            }

            @Override
            public void onAnimationRepeat(Animator animation) {
                animFactor = -1;
            }
        });
        animator.start();
    }
}

使用示例:

animateViewPager(pager, 10, 1000);

Edit2: ValueAnimator 是 Api 级别 11 的类.在调用此方法之前还要设置寻呼机适配器.

ValueAnimator is class for Api level 11. Also set pager adapter before calling this method.

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