在 ViewPager2 android 中检测过度滚动或页面结束事件

Question

ViewPager2

中没有过度滚动的方法，我需要检测过度滚动，以便在没有更多页面时可以将用户带回主页。

Answer 1

ViewPager2 没有用于过度滚动的公共方法，但是，可以通过监听来检测到

onPageScrollStateChanged

通常，当更改页面时，

onPageScrollStateChanged

中滚动状态的事件转换为

SCROLL_STATE_DRAGGING

->

SCROLL_STATE_SETTLING

->

SCROLL_STATE_IDLE

但是如果过度滚动，顺序是

SCROLL_STATE_DRAGGING

->

SCROLL_STATE_IDLE

private fun listenOverScroll(currentIndex: Int, size: Int) {
        var index = currentIndex
        var previousState =  ViewPager2.SCROLL_STATE_IDLE
        viewPager2.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {

            override fun onPageSelected(position: Int) {
                super.onPageSelected(position)
                index = position
            }

            override fun onPageScrollStateChanged(state: Int) {
                Log.d(TAG,"Index:: $index | state:: $state | prevState:: $previousState")
                super.onPageScrollStateChanged(state)
                if ((index >= size - 1 || index <= 0)// end of list. these checks can be 
                                                     // used individualy to detect end or start of pages
                        && previousState == ViewPager2.SCROLL_STATE_DRAGGING // from DRAGGING
                        && state == ViewPager2.SCROLL_STATE_IDLE) {          // to IDLE
                    Log.d(TAG,"OVERSCROLL:: Index:: $index | state:: $state | prevState:: $previousState")
                    //overscroll performed. do your work here
                }
                previousState = state
            }
        })
    }

Answer 2

我认为这是一个更清晰、更干净的解决方案。

private fun viewPagerScrollStateListener() {
    binding.viewPager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
        private var scrolling = false

        override fun onPageScrollStateChanged(state: Int) {
            super.onPageScrollStateChanged(state)
            scrolling = when (state) {
                ViewPager2.SCROLL_STATE_DRAGGING -> true
                ViewPager2.SCROLL_STATE_SETTLING -> true
                ViewPager2.SCROLL_STATE_IDLE -> {
                    if (scrolling && isLastPage()) {
                        // Scrolling has ended and we are on the last page
                        onEndScroll()
                    }
                    false
                }

                else -> false
            }
        }

        private fun isLastPage(): Boolean {
            return binding.viewPager.currentItem + 1 == adapter.itemCount
        }

        private fun onEndScroll() {
            Log.i("ViewPager", "End of scrolling")
        }
    })
}