Question

我正在尝试检测列表视图何时滚动超过某个固定阈值（以像素为单位）（第一项的一半）。不幸的是listview的getScrollY（）似乎总是返回滚动位置的0个instad。有没有办法按像素获取实际的滚动位置？

这是我尝试使用的代码，但据说它只返回0.

getListView().setOnScrollListener(new AbsListView.OnScrollListener() {
    public void onScroll(AbsListView view, int firstVisibleItem,
                         int visibleItemCount, int totalItemCount) {
        Log.d("scroll", "scroll: " + getListView().getScrollY());
    }

    public void onScrollStateChanged(AbsListView view, int scrollState) {
        if (scrollState == 0)
        Log.d("scroll", "scrolling stopped");
    }
});

Answer 1

Android中的ListView没有Y滚动的概念，因为内容的总高度未知。只知道显示内容的高度。

然而，可以使用以下hack来获取可见项目的当前位置/ Y滚动：

getListView().getChildAt(0).getTop();

Answer 2

您需要两件事来精确定义listView的滚动位置：

要获取当前位置：

int firstVisiblePosition = listView.getFirstVisiblePosition(); 
int topEdge=listView.getChildAt(0).getTop(); //This gives how much the top view has been scrolled.

要设置位置：

listView.setSelectionFromTop(firstVisiblePosition,0);
// Note the '-' sign...  
listView.scrollTo(0,-topEdge);

Answer 3

您可以尝试实施OnTouchListener并覆盖其onTouch(View v, MotionEvent event)并使用event.getX()和event.getY()获取x和y。我刚刚创建了一个用于在ListView行上滑动的演示，它将启用一个删除按钮，用于从ListView中删除特定项目。您可以将我的github中的源代码检查为ListItemSwipe。

Answer 4

Malachiasz答案的重构代码。此函数用于动态行的高度。

调用onScroll侦听器

private Dictionary<Integer, Integer> mListViewItemHeights = new Hashtable<Integer, Integer>(); 
private int getScrollY() {
        View child = mCardsListView.getChildAt(0); //this is the first visible row
        if (child == null) return 0;

        int scrollY = -child.getTop();

        mListViewItemHeights.put(mCardsListView.getFirstVisiblePosition(), child.getHeight());

        for (int i = 0; i < mCardsListView.getFirstVisiblePosition(); ++i) {
            Integer hei = mListViewItemHeights.get(i);

            //Manual add hei each row into scrollY
            if (hei != null)
                scrollY += hei;
        }

        return scrollY;
    }

getScrollY函数

{{1}}

Answer 5

也许对某人有用。快速滚动列表时，上一个答案的代码将不起作用。因为在这种情况下firstVisiblePosition可能会更改为不规则的。在我的代码中，我不使用数组来存储位置

fun setOnTouchScrollListener(lv: AbsListView, onTouchScrollListener: (isDown: Boolean, offset: Int?, isScrollWorking: Boolean) -> Unit) {

    var lastItemPosition: Int = -1
    var lastItemTop: Int? = null
    var lastItemHeight: Int? = null
    var lastScrollState: Int? = AbsListView.OnScrollListener.SCROLL_STATE_IDLE

    lv.setOnScrollListener(object : AbsListView.OnScrollListener {

        override fun onScroll(view: AbsListView, firstVisibleItem: Int, visibleItemCount: Int, totalItemCount: Int) {
            val child = lv.getChildAt(0)
            var offset: Int? = null
            var isDown: Boolean? = if (firstVisibleItem == lastItemPosition || lastItemPosition == -1) null else firstVisibleItem > lastItemPosition
            val dividerHeight = if (lv is ListView) lv.dividerHeight else 0
            val columnCount = if (lv is GridView) lv.numColumns else 1

            if (child != null) {
                if (lastItemPosition != -1) {
                    when (firstVisibleItem - lastItemPosition) {
                        0 -> {
                            isDown = if (lastItemTop == child.top) null else lastItemTop!! > child.top
                            offset = Math.abs(lastItemTop!! - child.top)
                        }
                        columnCount -> offset = lastItemHeight!! + lastItemTop!! - child.top + dividerHeight
                        -columnCount -> offset = child.height + child.top - lastItemTop!! + dividerHeight
                    }
                }

                lastItemPosition = firstVisibleItem
                lastItemHeight = child.height
                lastItemTop = child.top

                if (isDown != null && (offset == null || offset != 0)
                        && lastScrollState != AbsListView.OnScrollListener.SCROLL_STATE_IDLE) {
                    onTouchScrollListener(isDown, offset, true)
                }
            }
        }

        override fun onScrollStateChanged(view: AbsListView, scrollState: Int) {
            lastScrollState = scrollState
            if (scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE) {
                onTouchScrollListener(true, 0, false)
                lastItemPosition = -1
                lastItemHeight = null
                lastItemTop = null
            }
        }
    })
}

然后我们可以在列表视图滚动到阈值以上时使用

private var lastThresholdOffset = 0
private var thresholdHeight = some value

setOnTouchScrollListener(listView) { isDown: Boolean, offset: Int?, isScrollWorking: Boolean ->
    val offset = offset ?: if (isDown) 0 else thresholdHeight
    lastThresholdOffset = if (isDown) Math.min(thresholdHeight, lastThresholdOffset + offset)
    else Math.max(0, lastThresholdOffset - offset)

    val result = lastThresholdOffset > thresholdHeight
}

isScrollWorking-可以用于动画

Android ListView当前滚动位置Y像素

5 个答案: