- 1 year ago
VB.net SendMessage with CB_ADDSTRING unbalance the stack
The "unbalance the stack" error in VB.NET occurs when there is a mismatch between the calling convention used by the SendMessage
function and the calling convention expected by the function. This error is typically caused by incorrectly declaring the SendMessage
function with the wrong calling convention.
The SendMessage
function is part of the Windows API (user32.dll) and expects the StdCall
calling convention. However, by default, VB.NET uses the Cdecl
calling convention. To fix the "unbalance the stack" error, you need to explicitly specify the StdCall
calling convention when declaring the SendMessage
function.
Here's how you can correctly declare the SendMessage
function with the StdCall
calling convention in VB.NET:
vbnetImports System.Runtime.InteropServices
Public Class Form1
' Import the SendMessage function from the user32.dll library
Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As IntPtr, ByVal lParam As String) As IntPtr
' ComboBox handle
Private comboBoxHandle As IntPtr
' Add item to ComboBox
Private Sub AddItemToComboBox(itemText As String)
If comboBoxHandle <> IntPtr.Zero Then
' Use -1 as the index to add the new item to the end of the ComboBox
SendMessage(comboBoxHandle, &H143, New IntPtr(-1), itemText)
End If
End Sub
' Get ComboBox handle when the form loads
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
comboBoxHandle = comboBox1.Handle
End Sub
End Class
In the above example, we use Declare Function
with the Alias
attribute to explicitly specify the SendMessage
function with the StdCall
calling convention (Alias "SendMessageA"
). We also use ByVal
to pass parameters by value, as required by the StdCall
calling convention.
With the correct calling convention, the "unbalance the stack" error should be resolved, and your VB.NET application should be able to use the SendMessage
function with CB_ADDSTRING
properly.