Class MainWindow
　　Private Async Sub button_Click(sender As Object, e As RoutedEventArgs) Handles button.Click
　　　　' 検証処理の際に一時的に2つめのタブをアクティブにする
　　　　Await Threading.Dispatcher.Yield
　　　　Using New ReduceBlinkHelper(Me, BlinkBuffer)
　　　　　　tabControl.SelectedIndex = 1
　　　　　　Await Threading.Dispatcher.Yield
　　　　　　' 検証処理
　　　　　　GcSpreadGrid1.ValidateAll()
　　　　　　tabControl.SelectedIndex = 0
　　　　End Using
　　End Sub
End Class

' 描画のちらつきを防止する処理
Public Class ReduceBlinkHelper
　　Implements IDisposable

　　Private ReadOnly _bufferImage As Image
　　Sub New(window As Window, bufferImage As Image)
　　　　_bufferImage = bufferImage
　　　　BeginReduceBlink(window)
　　End Sub

　　Private Sub BeginReduceBlink(window As Window)
　　　　Dim beforeBlink = CaptureImage(window)
　　　　_bufferImage.Source = beforeBlink
　　　　_bufferImage.Visibility = Visibility.Visible
　　End Sub

　　Private Sub EndReduceBlink()
　　　　_bufferImage.Source = Nothing
　　　　_bufferImage.Visibility = Visibility.Collapsed
　　End Sub

　　Private Shared Function CaptureImage(window As Window) As ImageSource

　　　　Dim dpiScale = VisualTreeHelper.GetDpi(window)
　　　　Dim helper As New WindowInteropHelper(window)
　　　　Dim hWnd = helper.Handle

　　　　Dim clientPos As New System.Drawing.Point
　　　　ClientToScreen(hWnd, clientPos)

　　　　Dim clientRect As New Int32Rect
　　　　GetClientRect(hWnd, clientRect)

　　　　Dim windowRect As New Int32Rect
　　　　GetWindowRect(hWnd, windowRect)

　　　　clientRect.X = clientPos.X - windowRect.X
　　　　clientRect.Y = clientPos.Y - windowRect.Y

　　　　Using bitmap As New System.Drawing.Bitmap(clientRect.Width, clientRect.Height, PixelFormat.Format32bppArgb)
　　　　　　bitmap.SetResolution(dpiScale.PixelsPerInchX, dpiScale.PixelsPerInchY)
　　　　　　Using imageGraphics = System.Drawing.Graphics.FromImage(bitmap)
　　　　　　　　Dim dc = imageGraphics.GetHdc()
　　　　　　　　Dim windowDC = GetWindowDC(hWnd)

　　　　　　　　BitBlt(dc, 0, 0, clientRect.Width, clientRect.Height, windowDC, clientRect.X, clientRect.Y, SRCCOPY)

　　　　　　　　imageGraphics.ReleaseHdc(dc)
　　　　　　　　ReleaseDC(hWnd, windowDC)
　　　　　　End Using

　　　　　　Return ImageSourceFromBitmap(bitmap)
　　　　End Using
　　End Function

　　Private Shared Function ImageSourceFromBitmap(bmp As System.Drawing.Bitmap) As ImageSource
　　　　Dim ms As New MemoryStream
　　　　bmp.Save(ms, ImageFormat.Tiff)
　　　　ms.Position = 0
　　　　Dim tifDecoder As New TiffBitmapDecoder(ms, BitmapCreateOptions.None, BitmapCacheOption.None)
　　　　Return tifDecoder.Frames.First
　　End Function

#Region "　　PInvoke"

　　Private Declare Function ClientToScreen Lib "user32.dll" (hWnd As IntPtr, ByRef point As System.Drawing.Point) As Boolean
　　Private Declare Function GetClientRect Lib "user32.dll" (hWnd As IntPtr, ByRef rect As Int32Rect) As Boolean
　　Private Declare Function GetWindowRect Lib "user32.dll" (hWnd As IntPtr, ByRef rect As Int32Rect) As Boolean
　　Private Declare Function DeleteObject Lib "gdi32.dll" (hObject As IntPtr) As Boolean
　　Private Declare Function BitBlt Lib "gdi32.dll" (
　　　　hdcDest As IntPtr, xDest As Integer, yDest As Integer,
　　　　wDest As Integer, hDest As Integer, hdcSource As IntPtr,
　　　　xSrc As Integer, ySrc As Integer, rop As Integer) As Boolean
　　Private Declare Function GetWindowDC Lib "user32.dll" (ptr As IntPtr) As IntPtr
　　Private Declare Function ReleaseDC Lib "user32.dll" (hWnd As IntPtr, hDc As IntPtr) As Boolean
　　Private Const SRCCOPY = &HCC0020
#End Region

#Region "　　Implement IDisposable"
　　Private disposedValue As Boolean

　　Protected Overridable Sub Dispose(disposing As Boolean)
　　　　If Not disposedValue Then
　　　　　　If disposing Then
　　　　　　　　EndReduceBlink()
　　　　　　End If

　　　　　　disposedValue = True
　　　　End If
　　End Sub

　　Public Sub Dispose() Implements IDisposable.Dispose
　　　　Dispose(disposing:=True)
　　　　GC.SuppressFinalize(Me)
　　End Sub
#End Region
End Class