android - Android ListView 当前滚动位置 Y 像素

Question

我试图检测列表视图何时滚动超过像素的某个固定阈值（通过第一项的一半）。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");
    }
});

score 53 · Accepted Answer

Android 中的 ListView 没有 Y 滚动的概念，仅仅是因为内容的总高度未知。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();

score 2 · Accepted Answer

Malachiasz 答案的重构代码。此函数用于动态行的高度。

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;
    }

score 1 · Accepted Answer

您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);

score 0 · Accepted Answer

您可以尝试实现OnTouchListener并覆盖它并使用andonTouch(View v, MotionEvent event)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。你可以从我的 github 上查看源代码。event.getX()event.getY()ListItemSwipe

score 0 · Accepted Answer

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

android - Android ListView 当前滚动位置 Y 像素

5 回答 5

Related

Reference