DWMWA_USE_IMMERSIVE_DARK_MODE won't update

Question

Hi

Using this code to switch to dark and light mode for my .Net Framework 4.8 app only, but they won't apply until the form is resized, I can do:

Me.Width = Me.Width + 1

Me.Width = Me.Width - 1

But that's not the way to go, the code, Windows 10 21H2, any help is appreciated :)

Imports System.Runtime.InteropServices
Public Class Form1
    <DllImport("dwmapi.dll", CharSet:=CharSet.Unicode, PreserveSig:=True)>
    Public Shared Function DwmSetWindowAttribute(hwnd As IntPtr, attr As Integer, ByRef attrValue As Boolean, attrSize As Integer) As Integer
    End Function
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        DwmSetWindowAttribute(Me.Handle, 20, False, Runtime.InteropServices.Marshal.SizeOf(True))
    End Sub
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        DwmSetWindowAttribute(Me.Handle, 20, True, Runtime.InteropServices.Marshal.SizeOf(True))
    End Sub
End Class

Answer 1

A way is to force activation of caption, like :

SendMessage(Me.Handle, WM_NCACTIVATE, CType(False, IntPtr), IntPtr.Zero)
SendMessage(Me.Handle, WM_NCACTIVATE, CType(True, IntPtr), IntPtr.Zero)

with :

    <DllImport("User32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Public Shared Function SendMessage(hWnd As IntPtr, Msg As Integer, wParam As IntPtr, lParam As IntPtr) As Integer
    End Function
    Public Const WM_NCACTIVATE = &H86