Consolidated Scrolling - “Pixel by Pixel” + “Item by Item”

Question

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 th

Answer 1

Answer Actual Height Vs Viewport Height and Scrolling Issue

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;
                            }
                        }
                    }
                }
            }
        }

Answer 2

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