Windows 7开发：多点触摸 - 管理（动手实验）（下）

Windows 7开发：多点触摸 - 管理（动手实验）（下）2011-05-17 MSDN （代码片段 – MultiTouch – PictureTrackerManagerClass VB）
Visual Basic
Imports System.Windows
Imports System.Windows.Controls

Class PictureTrackerManager
     " Map between touch ids and picture trackers
     Private ReadOnly _pictureTrackerMap As New Dictionary （Of Integer, PictureTracker）
     Private ReadOnly _canvas As Canvas
     Public Sub New（ByVal canvas As Canvas）
         _canvas = canvas
     End Sub
     Public Sub ProcessDown（ByVal sender As Object, ByVal  args As StylusEventArgs）
         Dim location = args.GetPosition（_canvas）
         Dim pictureTracker = GetPictureTracker （args.StylusDevice.Id, location）

         If pictureTracker Is Nothing Then  Return

         pictureTracker.ProcessDown（location）
     End Sub
     Public Sub ProcessUp（ByVal sender As Object, ByVal  args As StylusEventArgs）
         Dim location = args.GetPosition（_canvas）
         Dim pictureTracker = GetPictureTracker （args.StylusDevice.Id）
         If pictureTracker Is Nothing Then  Return

         pictureTracker.ProcessUp（location）
         _pictureTrackerMap.Remove（args.StylusDevice.Id）
     End Sub
     Public Sub ProcessMove（ByVal sender As Object, ByVal  args As StylusEventArgs）
         Dim pictureTracker = GetPictureTracker （args.StylusDevice.Id）
         If pictureTracker Is Nothing Then  Return

         Dim location = args.GetPosition（_canvas）
         pictureTracker.ProcessMove（location）
     End Sub
     Private Function GetPictureTracker（ByVal touchId As  Integer） As PictureTracker
         Dim pictureTracker As PictureTracker =  Nothing
         _pictureTrackerMap.TryGetValue（touchId,  pictureTracker）
         Return pictureTracker
     End Function
     Private Function GetPictureTracker（ByVal touchId As  Integer, ByVal location As Point） As PictureTracker
         Dim pictureTracker As PictureTracker =  Nothing

         " See if we already track the picture with  the touchId
         If _pictureTrackerMap.TryGetValue（touchId,  pictureTracker） Then Return pictureTracker

         " Get the picture under the touch  location
         Dim picture = FindPicture（location）
         If picture Is Nothing Then Return  Nothing

         " See if we track the picture with other  ID
         pictureTracker = （From entry In  _pictureTrackerMap _
                           Where  entry.Value.Picture Is picture _
                           Select  entry.Value）.FirstOrDefault（）

         " First time
         If pictureTracker Is Nothing Then
             " Create new
             pictureTracker = New PictureTracker（）
             pictureTracker.Picture = picture
             BringPictureToFront（picture）
         End If
         " Remember the corelation between the touch  id and the picture
         _pictureTrackerMap（touchId） = pictureTracker
         Return pictureTracker
     End Function
     """ <summary>
     """ Find the picture in the touch location
     """ </summary>
     """ <param name="pointF">touch  location</param>
     """ <returns>The picture or null if no picture  exists in the touch
     """ location</returns>
     Private Function FindPicture（ByVal location As Point）  As Picture
         Dim result = VisualTreeHelper.HitTest（_canvas,  location）
         If result Is Nothing Then Return  Nothing

         Dim image = TryCast（result.VisualHit, Image）
         If image Is Nothing Then Return  Nothing

         Return TryCast（image.Parent, Picture）
     End Function
     Private Sub BringPictureToFront（ByVal picture As  Picture）
         If picture Is Nothing Then Return

         Dim children = （From child In _canvas.Children  _
                         Where child IsNot  picture _
                         Order By  Canvas.GetZIndex（child） _
                         Select  child）.ToArray（）

         For i = 0 To children.Length - 1
             Canvas.SetZIndex（children（i）, i）
         Next i
         Canvas.SetZIndex（picture, children.Length）
     End Sub
End Class