Unable to find RECT size with DwmGetWindowAttribute - vb.net

Question

I'm trying to find to find the size of the cmd.exe window which is started as a child. I like to use this size to resize my form accordingly. For some reason the size returned by DwmGetWindowAttribute is always zero, so I must be doing something wrong here, but I can't find it. Any help will be greatly appreciated.
Kind regards,
Eric
Imports System.Runtime.InteropServices
Public Class Form1
Private WithEvents Tmr As New Timer With {.Interval = 100}
Private Const HWND_BOTTOM As Integer = &H1
Private WithEvents proc As New Process
Public Const DWMWA_EXTENDED_FRAME_BOUNDS As Integer = 9
<DllImport("user32.dll", EntryPoint:="SetParent")>
Private Shared Function SetParent(ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr
End Function
<DllImport("user32.dll", EntryPoint:="SetWindowPos")>
Private Shared Function SetWindowPos(ByVal hWnd As IntPtr, ByVal hWndInsertAfter As IntPtr, ByVal X As Integer, ByVal Y As Integer, ByVal cx As Integer, ByVal cy As Integer, ByVal uFlags As UInteger) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function
<DllImport("dwmapi.dll")>
Shared Function DwmGetWindowAttribute(ByVal hwnd As IntPtr, ByVal dwAttribute As Integer, ByRef pvAttribute As RECT, ByVal cbAttribute As Integer) As Integer
End Function
Public Structure RECT
Public left, top, right, bottom As Integer
End Structure
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Text = "My title"
proc.EnableRaisingEvents = True
proc.StartInfo.FileName = "cmd"
proc.Start()
Tmr.Start()
End Sub
Private Sub Tmr_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles Tmr.Tick
If SetParent(proc.MainWindowHandle, Panel1.Handle) <> IntPtr.Zero Then
Tmr.Stop()
Dim Width As Integer
Dim Hight As Integer
Dim WindowRect As New RECT
DwmGetWindowAttribute(proc.MainWindowHandle, DWMWA_EXTENDED_FRAME_BOUNDS, WindowRect, Marshal.SizeOf(WindowRect))
Width = WindowRect.right - WindowRect.left
Hight = WindowRect.bottom - WindowRect.top
MessageBox.Show("Hight: " & Hight & " Width: " & Width)
'Me.Size = New Size(Width, Hight)
SetWindowPos(proc.MainWindowHandle, New IntPtr(HWND_BOTTOM), 0, 0, Panel1.ClientSize.Width, Panel1.ClientSize.Height, 0)
End If
End Sub
Private Sub Proc_Exited(ByVal sender As Object, ByVal e As System.EventArgs) Handles proc.Exited
Invoke(Sub() Close())
End Sub
End Class

Answer 1

After implementing all valuable additions of #Jimi, this is the code that works:
Imports System.Runtime.InteropServices
Public Class Form1
Private WithEvents proc As New Process
Public Const WM_NCLBUTTONDOWN As Long = &HA1
Public Const SW_SHOWMAXIMIZED As UInt32 = 3
Public Const WM_CLOSE = &H10
Public Const DWMWA_EXTENDED_FRAME_BOUNDS As Integer = 9
'Function to set the parent window
Private Declare Function SetParent Lib "user32" (ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr
'Function to set the child window position
Private Declare Function SetWindowPos Lib "user32" (ByVal hWnd As IntPtr, ByVal hWndInsertAfter As IntPtr, ByVal X As Integer, ByVal Y As Integer, ByVal cx As Integer, ByVal cy As Integer, ByVal uFlags As UInteger) As <MarshalAs(UnmanagedType.Bool)> Boolean
'Function to allow the child to be maximized
Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As IntPtr, ByVal nCmdShow As Int32) As Boolean
'Function to retrieve the initail child size
Private Declare Function DwmGetWindowAttribute Lib "dwmapi" (ByVal hwnd As IntPtr, ByVal dwAttribute As Integer, ByRef pvAttribute As RECT, ByVal cbAttribute As Integer) As Integer
'Function to set focus to the child window
Private Declare Function SetForegroundWindow Lib "user32" (ByVal hwnd As IntPtr) As Long
'Function used to set terminate child window
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As IntPtr, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer
'Rectangle size, used later to resize the form
Public Structure RECT
Public left, top, right, bottom As Integer
End Structure
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Text = "My title"
proc.EnableRaisingEvents = True
proc.StartInfo.FileName = "cmd"
proc.Start()
End Sub
Private Sub Tmr_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Shown
'Wait for 200 ms for the form to load
proc.WaitForExit(200)
Dim WindowRect As New RECT
Dim Width, Hight As Integer
'Retrieve the initial size of the child window
DwmGetWindowAttribute(proc.MainWindowHandle, DWMWA_EXTENDED_FRAME_BOUNDS, WindowRect, Marshal.SizeOf(WindowRect))
Width = WindowRect.right - WindowRect.left
Hight = WindowRect.bottom - WindowRect.top + 23
'Set the form size to the initial size of the child window
Me.Size = New Size(Width, Hight)
'When the child is started, move the child into the panel and maximize it
If SetParent(proc.MainWindowHandle, Panel1.Handle) <> IntPtr.Zero Then
SetWindowPos(proc.MainWindowHandle, IntPtr.Zero, 0, 0, Width, Height, 0)
ShowWindow(proc.MainWindowHandle, SW_SHOWMAXIMIZED)
End If
End Sub
'Exit form when child terminates
Private Sub Proc_Exited(ByVal sender As Object, ByVal e As System.EventArgs) Handles proc.Exited
Invoke(Sub() Close())
End Sub
'Set focus on child when the form is activated
Private Sub Form1_UnFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Activated
SetForegroundWindow(proc.MainWindowHandle)
End Sub
'Set focus on child when the parent titlebar is clicked
Protected Overrides Sub DefWndProc(ByRef m As System.Windows.Forms.Message)
If CLng(m.Msg) = WM_NCLBUTTONDOWN Then
SetForegroundWindow(proc.MainWindowHandle)
End If
MyBase.DefWndProc(m)
End Sub
'Properly terminate child when the form is closed by the user
Private Sub Form1_Closed(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Closed
SendMessage(proc.MainWindowHandle, WM_CLOSE, 0, 0)
End Sub
End Class
Kind regards,
Eric