OpenFileDialog 時檢視縮圖

原出處
Public Class Form1

' 宣告 API

Private Declare Function GetActiveWindow Lib "user32" () As Int32

Private Declare Function FindWindowExA Lib "user32" _
(ByVal hWnd1 As Int32, ByVal hWnd2 As Int32, _
ByVal lpsz1 As String, ByVal lpsz2 As String) As Int32

Private Declare Function SendMessageA Lib "user32" _
(ByVal hwnd As Int32, ByVal wMsg As Int32, _
ByVal wParam As Int32, ByVal lParam As Int32) As Int32

Private WithEvents tmr As Timer ' 宣告 Timer

Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
Using ofd As New OpenFileDialog
ofd.InitialDirectory = "D:\Photo\Gif"
tmr = New Timer With {.Interval = 99} ' 建購物件並初始化
If chkThumbnail.Checked Then tmr.Start() ' 勾選檢視縮圖則啟動 Timer
ofd.ShowDialog()
End Using
End Sub

' Timer 事件
Private Sub tmr_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles tmr.Tick
' 取得 Dialog 視窗 handle
Dim hwnd As Int32 = FindWindowExA(GetActiveWindow, 0, "SHELLDLL_DefView", vbNullString)
If hwnd > 0 Then
SendMessageA(hwnd, &H111, 28717, 0) ' 傳訊息 VIEW_THUMBNAIL
tmr.Stop() ' 停止 Timer
End If
End Sub
End Class