vb.net click button in another window

Imports System.Threading
Imports System.IO
Imports System.ComponentModel
Imports System.Text
Imports System.Runtime.InteropServices

Partial Public Class Form1
  Inherits Form

  <DllImport("user32")> _
  Public Shared Function EnumChildWindows(ByVal window As IntPtr, ByVal callback As EnumWindowProc, ByVal i As IntPtr) As <MarshalAs(UnmanagedType.Bool)> Boolean
  End Function

  <DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _
  Private Shared Function GetClassName(ByVal hWnd As IntPtr, ByVal lpClassName As StringBuilder, ByVal nMaxCount As Integer) As Integer
  End Function

  <DllImport("user32.dll", SetLastError:=True)> _
  Private Shared Function FindWindow(ByVal lpClassName As String, ByVal lpWindowName As String) As IntPtr
  End Function
  Private hWnd As IntPtr = FindWindow(Nothing, "Sample")

  <DllImport("user32.dll", SetLastError:=True)> _
  Private Shared Function PostMessage(ByVal hWnd As IntPtr, <MarshalAs(UnmanagedType.U4)> ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Boolean
  End Function

  Const WM_click As Integer = 245
  Const WM_KEYUP As Integer = &H101
  Const WM_CHAR As Integer = &H102

  Public Sub New()
    InitializeComponent()
   
  End Sub


  ''' <summary>
  ''' Returns a list of child windows
  ''' </summary>
  ''' <param name="parent">Parent of the windows to return</param>
  ''' <returns>List of child windows</returns>
  Public Shared Function GetChildWindows(ByVal parent As IntPtr) As List(Of IntPtr)
    Dim result As New List(Of IntPtr)()
    Dim listHandle As GCHandle = GCHandle.Alloc(result)
    Try
      Dim childProc As New EnumWindowProc(AddressOf EnumWindow)
      EnumChildWindows(parent, childProc, GCHandle.ToIntPtr(listHandle))
    Finally
      If listHandle.IsAllocated Then
        listHandle.Free()
      End If
    End Try
    Return result
  End Function

  ''' <summary>
  ''' Callback method to be used when enumerating windows.
  ''' </summary>
  ''' <param name="handle">Handle of the next window</param>
  ''' <param name="pointer">Pointer to a GCHandle that holds a reference to the list to fill</param>
  ''' <returns>True to continue the enumeration, false to bail</returns>
  Private Shared Function EnumWindow(ByVal handle As IntPtr, ByVal pointer As IntPtr) As Boolean
    Dim gch As GCHandle = GCHandle.FromIntPtr(pointer)
    Dim list As List(Of IntPtr) = TryCast(gch.Target, List(Of IntPtr))
    If list Is Nothing Then
      Throw New InvalidCastException("GCHandle Target could not be cast as List<IntPtr>")
    End If
    list.Add(handle)
    ' You can modify this to check to see if you want to cancel the operation, then return a null here
    Return True
  End Function

  ''' <summary>
  ''' Delegate for the EnumChildWindows method
  ''' </summary>
  ''' <param name="hWnd">Window handle</param>
  ''' <param name="parameter">Caller-defined variable; we use it for a pointer to our list</param>
  ''' <returns>True to continue enumerating, false to bail.</returns>
  Public Delegate Function EnumWindowProc(ByVal hWnd As IntPtr, ByVal parameter As IntPtr) As Boolean


  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    For Each child As IntPtr In GetChildWindows(FindWindow(Nothing, "Sample"))
      Dim sb As New StringBuilder(100)
      GetClassName(child, sb, sb.Capacity)

      If sb.ToString.Contains("BUTTON") Then
        Dim wparam As UInteger = 0 << 29 Or 0
        PostMessage(child, WM_click, 0, IntPtr.Zero)
      End If
    Next
  End Sub
End Class

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