合并滚动 - “逐像素"+“逐项" [英] Consolidated Scrolling - "Pixel by Pixel" + "Item by Item"
问题描述
我有一个拖放框架，其中已经存在滚动支持(逐像素滚动).这在未启用虚拟化的情况下效果很好，但如果启用了它就会搞砸.
由于滚动的逻辑基于视口高度，并且根据 MSDN，我们已经 -
I've a Drag-Drop framework in which scrolling support is already there (Pixel by Pixel scrolling). This works good in case Virtualization is not enabled but if it is enabled then it gets messed up.
As the logic of scrolling is based on Viewport height and as per MSDN we've -
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，则这些属性的值是与设备无关的像素.此外，如果启用了虚拟化，则 ExtentHeight 表示 - ScrollViewer 中的项目总数，而视口高度表示当前可见的项目数.
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.
所以滚动力工作我想要类似的东西——
So scrolling dint work i want something like--
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"，检查是否启用了虚拟化，但即使这样也能正常工作，因为我发现即使 CanContentScroll 为 true 视口高度 dint 表示可见项目的数量，但它等于实际高度.但是在另一个列表框上它显示 - 可见项目的数量.
I tried putting check of "CanContentScroll = false", checking Virtualization is enabled or not but even that dint work because i found that in one even if CanContentScroll is true Viewport height dint represent the number of items visible but it's equal to actual height. However on another listbox it shows - the number of items visible.
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);
}
}
}
我错觉虚拟化是罪魁祸首，但在检查了 IsVirtualization 属性后，我注意到虚拟化在这里不是问题(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 == 可见项目数但是在其他情况下视口高度 = 实际高度 ..
I was in illusion that virtualization is culprit but after checking IsVirtualization property, I noticed that virtualization is not an issue here (its true for both listboxes) .. Any Idea what can be the possible case ??
Issue is - I've 2 listboxes (almost similar) In one case i get
ViewPort Height == Number of Items visible
However in other case
ViewPort Height = Actual Height ..
可能的原因是什么??
推荐答案
代码:在启用虚拟化的情况下，我使用选定的项目来逐项目滚动
Code : I used selected Item to perfrom Item by Item scrolling in case of Virtualization enabled
// 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;
}
}
}
}
}
}
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