Android ListView 当前滚动位置 Y 像素

Question

我正在尝试检测列表视图何时滚动超过以像素为单位的某个固定阈值（第一项的一半）。不幸的是，listview 的 getScrollY() 似乎总是返回 0 而不是滚动位置。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，但如前所述，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，因为内容的总高度是未知的。只有显示内容的高度是已知的。

但是，可以使用以下 hack 获取可见项目的当前位置/Y 滚动：

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

Answer 2

Malachiasz 答案的重构代码。该函数用于动态行高。

调用 onScroll 监听器

mListView.setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {

            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                if (mCardsListView.getChildCount() > 0) {
                    int scrollY = getScrollY();
                }
            }
        });

getScrollY 函数

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;
    }

Answer 3

你需要两件事来精确定义 listView 的滚动位置：

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.

设置位置：

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

Answer 4

您可以尝试实现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。你可以在我的 github 上查看源代码ListItemSwipe。

Answer 5

也许它对某人有用。快速滚动列表时，先前答案的代码将不起作用。因为在这种情况下 firstVisiblePosition 可能会发生不规则的变化。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超过阈值时使用

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 - 可用于动画