Here's a little 5-minute glob of code I hacked together to handle dragging ScrollViewer content around with the mouse (or your finger).
It can also reverse the axes for "natural scrolling." There is also a Tolerance setting that is supposed to prevent it from scrolling if you only drag it a little bit. I did this because my crappy touchscreen driver has a lot of jitter.
I claim no responsibility if it explodes or otherwise has undesired effects. :)
using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Controls;
namespace MouseExtensions
{
public class MouseDragBehavior
{
public static readonly DependencyProperty ToleranceProperty = DependencyProperty.RegisterAttached("Tolerance", typeof(double), typeof(MouseDragBehavior), new FrameworkPropertyMetadata((double)10));
public static double GetTolerance(DependencyObject d)
{
return (double)d.GetValue(ToleranceProperty);
}
public static void SetTolerance(DependencyObject d, double value)
{
d.SetValue(ToleranceProperty, value);
}
public static readonly DependencyProperty ReverseAxisProperty = DependencyProperty.RegisterAttached("ReverseAxis", typeof(bool), typeof(MouseDragBehavior), new FrameworkPropertyMetadata((bool)false));
public static bool GetReverseAxis(DependencyObject d)
{
return (bool)d.GetValue(ReverseAxisProperty);
}
public static void SetReverseAxis(DependencyObject d, bool value)
{
d.SetValue(ReverseAxisProperty, value);
}
private static readonly DependencyProperty DragStartPointProperty = DependencyProperty.RegisterAttached("DragStartPoint", typeof(Point), typeof(MouseDragBehavior), new FrameworkPropertyMetadata((Point)new Point()));
private static Point GetDragStartPoint(DependencyObject d)
{
return (Point)d.GetValue(DragStartPointProperty);
}
private static void SetDragStartPoint(DependencyObject d, Point value)
{
d.SetValue(DragStartPointProperty, value);
}
private static readonly DependencyProperty DragLastPointProperty = DependencyProperty.RegisterAttached("DragLastPoint", typeof(Point), typeof(MouseDragBehavior), new FrameworkPropertyMetadata((Point)new Point()));
private static Point GetDragLastPoint(DependencyObject d)
{
return (Point)d.GetValue(DragLastPointProperty);
}
private static void SetDragLastPoint(DependencyObject d, Point value)
{
d.SetValue(DragLastPointProperty, value);
}
public static readonly DependencyProperty HandleDragProperty = DependencyProperty.RegisterAttached("HandleDrag", typeof(bool), typeof(MouseDragBehavior), new FrameworkPropertyMetadata((bool)false, new PropertyChangedCallback(OnHandleDragChanged)));
public static bool GetHandleDrag(DependencyObject d)
{
return (bool)d.GetValue(HandleDragProperty);
}
public static void SetHandleDrag(DependencyObject d, bool value)
{
d.SetValue(HandleDragProperty, value);
}
private static void OnHandleDragChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
ScrollViewer scrollViewer = d as ScrollViewer;
if ((bool)e.NewValue)
{
scrollViewer.PreviewMouseDown += new MouseButtonEventHandler(target_PreviewMouseDown);
scrollViewer.PreviewMouseMove += new MouseEventHandler(target_PreviewMouseMove);
scrollViewer.PreviewMouseUp += new MouseButtonEventHandler(target_PreviewMouseUp);
scrollViewer.MouseLeave += new MouseEventHandler(target_MouseLeave);
}
else
{
scrollViewer.PreviewMouseDown -= new MouseButtonEventHandler(target_PreviewMouseDown);
scrollViewer.PreviewMouseMove -= new MouseEventHandler(target_PreviewMouseMove);
scrollViewer.PreviewMouseUp -= new MouseButtonEventHandler(target_PreviewMouseUp);
scrollViewer.MouseLeave -= new MouseEventHandler(target_MouseLeave);
}
}
private static bool IsDragging(ScrollViewer scrollViewer)
{
Point posNow = Mouse.GetPosition(scrollViewer);
return ((Math.Abs(GetDragStartPoint(scrollViewer).X - posNow.X) > GetTolerance(scrollViewer)) || (Math.Abs(GetDragStartPoint(scrollViewer).Y - posNow.Y) > GetTolerance(scrollViewer)));
}
private static void target_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
var scrollViewer = (ScrollViewer)sender;
var mousePos = e.GetPosition(scrollViewer);
scrollViewer.CaptureMouse();
if (GetDragLastPoint(scrollViewer) == new Point())
{
SetDragStartPoint(scrollViewer, mousePos);
SetDragLastPoint(scrollViewer, mousePos);
}
if (IsDragging(scrollViewer))
{
e.Handled = true;
return;
}
else
scrollViewer.ReleaseMouseCapture();
}
private static void target_PreviewMouseMove(object sender, MouseEventArgs e)
{
var scrollViewer = (ScrollViewer)sender;
if (GetDragLastPoint(scrollViewer) != new Point())
{
Point posNow = e.GetPosition(scrollViewer);
double dX = posNow.X - GetDragLastPoint(scrollViewer).X;
double dY = posNow.Y - GetDragLastPoint(scrollViewer).Y;
SetDragLastPoint(scrollViewer, posNow);
if (!IsDragging(scrollViewer))
return;
if (GetReverseAxis(scrollViewer))
{
scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset + dX);
scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + dY);
}
else
{
scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset - dX);
scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - dY);
}
}
e.Handled = true;
}
private static void target_PreviewMouseUp(object sender, MouseButtonEventArgs e)
{
var scrollViewer = (ScrollViewer)sender;
if (GetDragLastPoint(scrollViewer) != new Point() && IsDragging(scrollViewer))
{
e.Handled = true;
scrollViewer.ReleaseMouseCapture();
}
Reset(scrollViewer);
}
private static void target_MouseLeave(object sender, MouseEventArgs e)
{
var scrollViewer = (ScrollViewer)sender;
Reset(scrollViewer);
}
private static void Reset(ScrollViewer scrollViewer)
{
SetDragLastPoint(scrollViewer, new Point());
SetDragStartPoint(scrollViewer, new Point());
}
}
}
To use it simply reference the namespace and set MouseDragBehavior.HandleDrag to true in your
Question
Eric Veteran
Here's a little 5-minute glob of code I hacked together to handle dragging ScrollViewer content around with the mouse (or your finger).
It can also reverse the axes for "natural scrolling." There is also a Tolerance setting that is supposed to prevent it from scrolling if you only drag it a little bit. I did this because my crappy touchscreen driver has a lot of jitter.
I claim no responsibility if it explodes or otherwise has undesired effects. :)
To use it simply reference the namespace and set MouseDragBehavior.HandleDrag to true in your
ScrollViewer declaration:
Link to comment
Share on other sites
3 answers to this question
Recommended Posts