mcs/class/referencesource/System.Activities.Presentation/System.Activities.Presentation/System/Activities/Presentation/View/AutoScrollHelper.cs

   1 //----------------------------------------------------------------
   2 // Copyright (c) Microsoft Corporation.  All rights reserved.
   3 //----------------------------------------------------------------
   4
   5 namespace System.Activities.Presentation.View
   6 {
   7     using System;
   8     using System.Windows;
   9     using System.Windows.Media;
  10     using System.Windows.Controls;
  11     using System.Windows.Input;
  12
  13     internal static class AutoScrollHelper
  14     {
  15         const int scrollBuffer = 30;
  16
  17         public static void AutoScroll(MouseEventArgs e, DependencyObject element, double offsetPerScroll)
  18         {
  19             FrameworkElement logicalView = element as FrameworkElement;
  20             while (element != null)
  21             {
  22                 element = VisualTreeHelper.GetParent(element);
  23                 if (element != null && element is ScrollViewer)
  24                 {
  25                     break;
  26                 }
  27             }
  28             ScrollViewer scrollViewer = element as ScrollViewer;
  29             if (scrollViewer != null)
  30             {
  31                 AutoScroll(e.GetPosition(scrollViewer), scrollViewer, logicalView != null ? e.GetPosition(logicalView) : (Point?)null, logicalView,
  32                      25, 25, offsetPerScroll);
  33             }
  34         }
  35
  36         public static void AutoScroll(DragEventArgs e, ScrollViewer scrollViewer, double offsetPerScroll)
  37         {
  38             AutoScroll(e.GetPosition(scrollViewer), scrollViewer, offsetPerScroll);
  39         }
  40
  41         public static void AutoScroll(Point position, ScrollViewer scrollViewer, double offsetPerScroll)
  42         {
  43             AutoScroll(position, scrollViewer, null, null,
  44                 50, 50, offsetPerScroll);
  45         }
  46
  47         static void AutoScroll(Point positionInScrollViewer, ScrollViewer scrollViewer, Point? positionInLogicalView, FrameworkElement logicalView, double scrollOnDragThresholdX, double scrollOnDragThresholdY, double scrollOnDragOffset)
  48         {
  49             double scrollViewerWidth = scrollViewer.ActualWidth;
  50             double scrollViewerHeight = scrollViewer.ActualHeight;
  51
  52             double logicalViewWidth = 0;
  53             double logicalViewHeight = 0;
  54             if (logicalView != null)
  55             {
  56                 logicalViewWidth = logicalView.ActualWidth;
  57                 logicalViewHeight = logicalView.ActualHeight;
  58             }
  59
  60             double heightToScroll = 0;
  61             double widthToScroll = 0;
  62
  63             if (positionInScrollViewer.X > (scrollViewerWidth - scrollOnDragThresholdX)
  64                 && (positionInLogicalView == null
  65                    || positionInLogicalView.Value.X < (logicalViewWidth - scrollBuffer)))
  66             {
  67                 widthToScroll = scrollOnDragOffset;
  68             }
  69             else if (positionInScrollViewer.X < scrollOnDragThresholdX
  70                 && (positionInLogicalView == null
  71                    || positionInLogicalView.Value.X > scrollBuffer))
  72             {
  73                 widthToScroll = -scrollOnDragOffset;
  74             }
  75
  76             if (positionInScrollViewer.Y > (scrollViewerHeight - scrollOnDragThresholdY)
  77                 && (positionInLogicalView == null
  78                     || positionInLogicalView.Value.Y < logicalViewHeight - scrollBuffer))
  79             {
  80                 heightToScroll = scrollOnDragOffset;
  81             }
  82             else if (positionInScrollViewer.Y < scrollOnDragThresholdY
  83                 && (positionInLogicalView == null
  84                    || positionInLogicalView.Value.Y > scrollBuffer))
  85             {
  86                 heightToScroll = -scrollOnDragOffset;
  87             }
  88
  89             if (widthToScroll != 0 || heightToScroll != 0)
  90             {
  91                 scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + heightToScroll);
  92                 scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset + widthToScroll);
  93             }
  94         }
  95     }
  96 }