Win32 EM_GETTEXTEX causing the application to crash.

Question

Hi,

Well this question is related to use of Win32 API. I am trying to get text of a RichTextBox which is located in one of my text application. I am trying to use EM_GETTEXTEX message  to collect the data.

Here is the code

            Dim Struct As New GetTexTex
            Struct.cb = GetTextLength(hWnd, FlagVal)  'A wrapper function over WIN32 API Rich text box gettext message
            Struct.Flags = FlagVal
            Struct.CodePage = 1200
            Struct.LPBOOL = Nothing
            Struct.LPCSTR = Nothing

            Dim text As New StringBuilder("", CType(Struct.cb, Integer))
            Try
                Win32_user32_Functions.SendMessage(hWnd, EM_GETTEXTEX, Struct, text)
                Return text.ToString
            Catch ex As Exception
                Return text.ToString
            End Try

 'Structure definition

    Public Structure GetTexTex
        Dim cb As Long
        Dim Flags As RichTextGetTextTexEnum
        Dim CodePage As Long
        Dim LPCSTR As String
        Dim LPBOOL As String
    End Structure

'Enum Def

    Public Enum RichTextGetTextTexEnum
        GT_DEFAULT = 0
        GT_SELECTION
        GT_USECRLF = 1&
    End Enum

When I run this code it causes the application to crash. Can some one tell me what is it that I am doing wrong?

I tried sending the string both byval and byref. Each makes the test app to crash everytime.

A help or pointer will help a lot.

Regards

Virender

---

Regards Virender

Answer 1

These are VB6 declarations that don't work since 2002.

Please also show the declarations for GetTextLength, hWnd, EM_GETTEXTEX and SendMessage.

What's the reason for "Return text.ToString" in the Try block and also in the catch block?

---

Armin

Answer 2

You can pick out the parts you need from this (untested!) code: 

Imports System.Runtime.InteropServices
Imports System.Text

Public Class Main
   Shared Sub main()

   End Sub

   Const WM_USER As UInteger = &H400

   Const EM_GETTEXTEX As UInteger = WM_USER + 94
   Const EM_GETTEXTLENGTHEX As UInteger = WM_USER + 95

   Public Shared ReadOnly E_INVALIDARG As New IntPtr(&H80070057)

   <Flags()> _
   Public Enum GetTextFlags As UInteger
      [Default] = 0
      UserCrLF = 1
      Selection = 2
      RawText = 4
      NoHiddenText = 8
   End Enum


   <Flags()> _
   Public Enum GetTextLengthFlags As UInteger
      [Default] = 0
      UseCrLf = 1
      Precise = 2
      Close = 4
      NumChars = 8
      NumBytes = 16
   End Enum

   <StructLayout(LayoutKind.Sequential)> _
   Public Structure GetTextEx
      Public cb As UInt32
      Public Flags As GetTextFlags
      Public CodePage As UInt32
      <MarshalAs(UnmanagedType.LPStr)> Public DefaultChar As String
      Public UsedDefChar As IntPtr
   End Structure

   <StructLayout(LayoutKind.Sequential)> _
   Public Structure GetTextLengthEx
      Public flags As GetTextLengthFlags
      Public codepage As UInt32
   End Structure

   Public Declare Auto Function SendMessage Lib "user32.dll" ( _
      ByVal hWnd As IntPtr, ByVal Msg As UInteger, _
      ByRef wParam As GetTextEx, ByVal lParam As System.Text.StringBuilder) _
      As IntPtr

   Public Declare Auto Function SendMessage Lib "user32.dll" ( _
      ByVal hWnd As IntPtr, ByVal Msg As UInteger, _
      ByRef wParam As GetTextLengthEx, ByVal lParam As IntPtr) _
      As IntPtr

   Shared Function GetText( _
      ByVal hWnd As IntPtr, _
      ByVal GetLengthFlags As GetTextLengthFlags, _
      ByVal GetTextFlags As GetTextFlags) As String

      Dim Struct As GetTextEx
      Dim sb As StringBuilder

      Struct.cb = CUInt(GetTextLength(hWnd, GetLengthFlags))
      Struct.Flags = GetTextFlags
      Struct.CodePage = 1200

      sb = New StringBuilder(CInt(Struct.cb))

      SendMessage(hWnd, EM_GETTEXTEX, Struct, sb)
      Return sb.ToString

   End Function
   Shared Function GetTextLength(ByVal hWnd As IntPtr, ByVal flags As GetTextLengthFlags) As Integer

      Dim struct As GetTextLengthEx
      Dim result As IntPtr

      struct.flags = flags

      result = SendMessage(hWnd, EM_GETTEXTLENGTHEX, struct, IntPtr.Zero)

      If result = E_INVALIDARG Then
         Throw New System.ComponentModel.Win32Exception("Invalid argument calling SendMessage")
      Else
         Return CInt(result)
      End If

   End Function

End Class

Armin

Answer 3

'Get text length is defined as this

        Public Shared Function GetTextLength(ByVal hWnd As IntPtr, ByVal FlagVal As RichTextGetTextTexEnum) As Long
            Dim Struct As New RichTextGetTextLengthEx
            Struct.Codepage = 1200
            Struct.Flags = FlagVal
            Try
                Return Win32_user32_Functions.SendMessage(hWnd, RichTextBoxMessages.EM_GETTEXTLENGTHEX, Struct, 0)
            Catch ex As Exception
                Return -100
            End Try
        End Function

This function uses

Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal Msg As RichTextBoxMessages, ByRef wParam As RichTextGetTextLengthEx, ByVal lParam As Integer) As IntPtr

dim hWnd as Intptr

EM_GETTEXTLENGTHEX = (1024 + 95)

Return text is just the way I have implemented it. It gives back the text from the richtext edit box

Thanks

And hoping for a reply from you

---

Regards Virender

Answer 4

Thanks Armin. I will try to use this code and will post you back on the result.

---

Regards Virender

Answer 5

SOlution given doesnt work. It is still crashing the application.

---

Regards Virender

Answer 6

SOlution given doesnt work. It is still crashing the application.

Again, please show the error line and all related declarations. We do not know which parts you've changed.

---

Armin

Answer 7

Well it seems that the code given earlier is working. It was the way I was passing values. Thanks for all your help and sorry for replying to it so late.

---

Regards Virender