合并滚动-“逐像素” + “逐项”

Question

我有一个拖放框架，其中已经存在滚动支持（逐像素滚动）。在未启用虚拟化的情况下，这很有效，但如果启用了虚拟化，那么它就会变得混乱。
由于滚动的逻辑基于视口高度，并且根据 MSDN，我们 -

MSDN - 如果 CanContentScroll 为 true，则 ExtentHeight、ScrollableHeight、ViewportHeight 和 VerticalOffset 属性的值是项目数。如果 CanContentScroll 为 false，则这些属性的值为设备独立像素。另外，如果启用虚拟化，则 ExtentHeight 表示 - ScrollViewer 中的项目总数，视口高度表示当前可见的项目数。

因此，滚动功能工作我想要类似的东西 -

ScrollToContent(ScrollViewer, CurrentMousePositionWRTScrollViewer)
{ 
   if(ScrollViewer's Viewport Height is in terms of Pixel)
{
----------Do Pixel by Pixel Scrolling --------
}
else if(ScrollViewer's Viewport Height represents number of items visible)
{ 
--------- Do Item by Item Scrolling ---------
}

我尝试检查“CanContentScroll = false”，检查虚拟化是否启用，但即使该功能也有效，因为我发现即使 CanContentScroll 为 true，视口高度功能也代表了项目可见，但等于实际高度。然而，在另一个列表框中，它显示 - 可见项目的数量。

滚动的实际代码 -

private void ScrollToContent(ScrollViewer scrollViewer, Point point)
    {
        double verticalScrollOffset = 0.0;
        double scrollDifference = 30.0;
        double scrollDefaultOffset = 40.0;

        if (scrollViewer == null) return;
        if (scrollViewer.ViewportHeight != scrollViewer.ExtentHeight)
        {
                if (scrollViewer.ViewportHeight - point.Y < scrollDifference)
                {
                    // See if we need to scroll down
                    verticalScrollOffset = scrollDefaultOffset;
                }
                else if (point.Y < scrollDifference)
                {
                    // See if we need to scroll up
                    verticalScrollOffset = -scrollDefaultOffset;
                }
                // Scroll up or down
                if (verticalScrollOffset != 0.0)
                {
                    verticalScrollOffset += scrollViewer.VerticalOffset;
                    if (verticalScrollOffset < 0.0)
                    {
                        verticalScrollOffset = 0.0;
                    }
                    else if (verticalScrollOffset > scrollViewer.ScrollableHeight)
                    {
                        verticalScrollOffset = scrollViewer.ScrollableHeight;
                    }
                    scrollViewer.ScrollToVerticalOffset(verticalScrollOffset);
                }
        }
    }

我幻想虚拟化是罪魁祸首，但在检查 IsVirtualization 属性后，我注意到虚拟化在这里不是问题（这对于两个列表框都是如此）..任何想法可能是什么情况？？
问题是 - 我有 2 个列表框（几乎相似） 在一种情况下我得到 视口高度 == 可见项目数 然而在其他情况下 视口高度 = 实际高度 ..

可能的原因是什么？

Answer 1

bool isVirtualizing = (bool)scrollViewer.GetValue(VirtualizingStackPanel.IsVirtualizingProperty);
VirtualizationMode mode = (VirtualizationMode)scrollViewer.GetValue(VirtualizingStackPanel.VirtualizationModeProperty);

Answer 2

回答实际高度与视口高度和滚动问题

代码：我使用选定的项目在启用虚拟化的情况下执行逐项滚动

 // Manage vertical scrolling. 
        if (scrollViewer.ViewportHeight != scrollViewer.ExtentHeight)
        {
            // NOTE :MSDN- If CanContentScroll is true, the values of the ExtentHeight, ScrollableHeight, ViewportHeight, and VerticalOffset
            // properties are number of items. If CanContentScroll is false, the values of these properties are Device Independent Pixels.
            // Also If Virtualization is Enabled then ExtentHeight Represents - TotalNumber of Items in ScrollViewer and Viewport Height
            // Represents Count of Items currently visible.
            if (scrollViewer.CanContentScroll == false)
            {
                if (scrollViewer.ViewportHeight - point.Y < scrollDifference)
                {
                    // See if we need to scroll down
                    verticalScrollOffset = scrollDefaultOffset;
                }
                else if (point.Y < scrollDifference)
                {
                    // See if we need to scroll up
                    verticalScrollOffset = -scrollDefaultOffset;
                }

                // Scroll up or down
                if (verticalScrollOffset != 0.0)
                {
                    verticalScrollOffset += scrollViewer.VerticalOffset;

                    if (verticalScrollOffset < 0.0)
                    {
                        verticalScrollOffset = 0.0;
                    }
                    else if (verticalScrollOffset > scrollViewer.ScrollableHeight)
                    {
                        verticalScrollOffset = scrollViewer.ScrollableHeight;
                    }

                    scrollViewer.ScrollToVerticalOffset(verticalScrollOffset);
                }
            }
            else
            {
                if (scrollViewer != null)
                {
                    // To ControlScrolling Speed - as we're doing Item By Item Scrolling now, it would be quite fast so add a time gap.
                    if (DateTime.Now.Subtract(lastScrollTime).TotalMilliseconds > 200)
                    {
                        if (scrollViewer.ActualHeight - point.Y < scrollDifference)
                        {
                            // See if we need to scroll down
                            verticalScrollOffset = scrollDefaultOffset;
                        }
                        else if (point.Y < scrollDifference)
                        {
                            // See if we need to scroll up
                            verticalScrollOffset = -scrollDefaultOffset;
                        }

                        if (verticalScrollOffset != 0.0)
                        {
                            // Scroll Content upwards 
                            if (verticalScrollOffset < 0 && scrollViewer.VerticalOffset > 0) // Also check if there are any non visible elements in scrollviewer
                            {
                                scrollViewer.LineUp();
                                lastScrollTime = DateTime.Now;
                            }
                            else if (verticalScrollOffset > 0 &&
                                scrollViewer.VerticalOffset < scrollViewer.ExtentHeight - scrollViewer.ViewportHeight)
                            {
                                scrollViewer.LineDown();
                                lastScrollTime = DateTime.Now;
                            }
                        }
                    }
                }
            }
        }