Is it possible to implement smooth scroll in a WPF listview?

Question

Is it possible to implement smooth scroll in a WPF listview like how it works in Firefox?
When the Firefox browser contained all listview items and you hold down the middle mouse button (but not release), and drag it, it should smoothly scroll the listview items. When you release it should stop.

It looks like this is not possible in winforms, but I am wondering if it is available in WPF?

Answer 1

You can achieve smooth scrolling but you lose item virtualisation, so basically you should use this technique only if you have few elements in the list:

Info here: Smooth scrolling on listbox

Answer 2

Try setting the ScrollViewer.CanContentScroll attached property to false on the ListView. But like Pop Catalin said, you lose item virtualization, meaning all the items in the list get loaded and populated at once, not when a set of items are needed to be displayed - so if the list is huge, it could cause some memory and performance issues.

Answer 3

It is indeed possible to do what you're asking, though it will require a fair amount of custom code.

Normally in WPF a ScrollViewer uses what is known as Logical Scrolling, which means it's going to scroll item by item instead of by an offset amount. The other answers cover some of the ways you can change the Logical Scrolling behavior into that of Physical Scrolling. The other way is to make use of the ScrollToVertialOffset and ScrollToHorizontalOffset methods exposed by both ScrollViwer and IScrollInfo.

To implement the larger part, the scrolling when the mouse wheel is pressed, we will need to make use of the MouseDown and MouseMove events.

<ListView x:Name="uiListView"
    Mouse.MouseDown="OnListViewMouseDown"
    Mouse.MouseMove="OnListViewMouseMove"
    ScrollViewer.CanContentScroll="False">
    ....
</ListView>

In the MouseDown, we are going to record the current mouse position, which we will use as a relative point to determine which direction we scroll in. In the mouse move, we are going to get the ScrollViwer component of the ListView and then Scroll it accordingly.

private Point myMousePlacementPoint;

private void OnListViewMouseDown(object sender, MouseButtonEventArgs e)
{
 if (e.MiddleButton == MouseButtonState.Pressed)
 {
  myMousePlacementPoint = this.PointToScreen(Mouse.GetPosition(this));
 }
}

private void OnListViewMouseMove(object sender, MouseEventArgs e)
{
 ScrollViewer scrollViewer = ScrollHelper.GetScrollViewer(uiListView) as ScrollViewer;

 if (e.MiddleButton == MouseButtonState.Pressed)
 {
  var currentPoint = this.PointToScreen(Mouse.GetPosition(this));

  if (currentPoint.Y < myMousePlacementPoint.Y)
  {
   scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - 3);
  }
  else if (currentPoint.Y > myMousePlacementPoint.Y)
  {
   scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + 3);
  }

  if (currentPoint.X < myMousePlacementPoint.X)
  {
   scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset - 3);
  }
  else if (currentPoint.X > myMousePlacementPoint.X)
  {
   scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset + 3);
  }
 }
}

public static DependencyObject GetScrollViewer(DependencyObject o)
{
 // Return the DependencyObject if it is a ScrollViewer
 if (o is ScrollViewer)
 { return o; }

 for (int i = 0; i < VisualTreeHelper.GetChildrenCount(o); i++)
 {
  var child = VisualTreeHelper.GetChild(o, i);

  var result = GetScrollViewer(child);
  if (result == null)
  {
   continue;
  }
  else
  {
   return result;
  }
 }
 return null;
}

There's some areas it's lacking as it's just a proof of concept but it should definitely get you started in the right direction. To have it constantly scroll once the mouse is moved away from the initial MouseDown point, the scrolling logic could go into a DispatcherTimer or something similar.