How To Resize RichTextbox Control with Endless Bottom (257849)

MORE INFORMATION

This sample demonstrates how to intercept windows messages and check for a specific message, EN_REQUESTRESIZE. This is accomplished by creating a message handler (hook) and sending an event mask to the parent window. The event mask tells the form what type of messages the control is sending. If you are unfamiliar with message handlers, please see the "References" section of this article.

WARNING: Failure to unhook a window before its imminent destruction results in application errors, Invalid Page Faults, and data loss. This is due the fact that the new WindowProc function being pointed to no longer exists, but the window has not been notified of the change. Always unhook the sub-classed window upon unloading the sub-classed form or exiting the application. This is especially important while debugging an application that uses this technique within the Microsoft Visual Basic Development Environment. Pressing the End button or selecting End from the Run menu without unhooking causes an Invalid Page Fault and closes Microsoft Visual Basic.

Sample Code

1. Start a new Visual Basic Standard EXE project. Form1 is created by default.
2. On the Project menu, select Components. Check the Rich Textbox and Common Dialog controls, and then click OK.
3. Add a CommandButton, a CommonDialog, and a RichTextBox control to Form1.
4. In the Properties window, set the ScrollBars property of RichTextBox1 to 2-rtfVertical.
5. Add the following code to the General Declarations section of Form1:

   Option Explicit
   
   Private Sub Form_Load()
   ' Create a Hook and populate a global variable with the Richtextbox hwnd.
      Call NewWindowProc(Me.hWnd)
      RichWnd = RichTextBox1.hWnd
   End Sub
   
   Private Sub Command1_Click()
   ' Load a file into the richtextbox control
      With CommonDialog1
         .Filter = "All Files|*.*|Text Files|*.txt|RTF Files|*.rtf"
         .ShowOpen
         RichTextBox1.FileName = .FileName
      End With
   End Sub
   
   Private Sub Form_Resize()
   ' 1.)Populate global variables with the Height and Width of the 
   '   Richtextbox control.
   ' 2.)Set an event mask for the Richtextbox control.
   ' 3.)Send an EM_REQUESTRESIZE Message to the Form.
   
      gblWidth = RichTextBox1.Width / Screen.TwipsPerPixelX
      gblHeight = ((Form1.Height - RichTextBox1.Top) - 450) / _
                  Screen.TwipsPerPixelY
      Call SetMask(RichWnd)
      Call SendMessage(RichWnd, EM_REQUESTRESIZE, 0, 0)
   End Sub
   
   Private Sub Form_Unload(Cancel As Integer)
      Call ResetWindProc(Me.hWnd) ' Remove the Windows Hook
   End Sub
   					

6. On the Project menu, select Add Module to add a BAS module to the project. Module1 is created by default.
7. Add the following code to General Declarations section of Module1:

   Option Explicit
   
   ' Private Variables
   
   Private rResize As REQSIZE ' <--- Pointer to REQSIZE Structure
   Private MaskHdr As nmhdr   ' <--- Pointer to nmhdr Structure
   Private OldWndProc As Long
   Private Const GWL_WNDPROC = (-4)
   Private Const WM_USER = &H400
   Private Const WM_NOTIFY = &H4E
   Private Const SWP_NOMOVE = &H2
   Private Const SWP_SHOWWINDOW = &H40
   Private Const EM_GETEVENTMASK = (WM_USER + 59)
   Private Const EM_SETEVENTMASK = (WM_USER + 69)
   Private Const ENM_REQUESTRESIZE As Long = &H40000
   Private Const EN_REQUESTRESIZE = &H701
   
   ' Public Variables
   
   Public gblWidth As Long     ' <--- Var Holder for Richtext Width
   Public gblHeight As Long    ' <--- Var Holder for Richtext Height
   Public Const EM_REQUESTRESIZE = (WM_USER + 65)
   Public Const VBNullPtr = 0&
   Public RichWnd As Long      ' <--- Var Holder for Richtext Hwnd
   
   Private Type nmhdr
      hwndFrom As Long
      idfrom As Long
      code As Long
   End Type
   
   Private Type rect
      Left As Long
      Top As Long
      Right As Long
      Bottom As Long
   End Type
   
   Private Type REQSIZE
      nmhdr As nmhdr
      rect As rect
   End Type
   
   Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
      (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
      ByVal lParam As Long) As Long
   
   Private Declare Function SetWindowLong Lib "user32" Alias _ 
      "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, _ 
      ByVal dwNewLong As Long) As Long
   
   Private Declare Function CallWindowProc Lib "user32" _
      Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, _
      ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, _
      ByVal lParam As Long) As Long
   
   Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
      (Destination As Any, Source As Any, ByVal Length As Long)
   
   Public Declare Function SetWindowPos Lib "user32" _
      (ByVal hwnd As Long, ByVal hWndInsAfter As Long, ByVal x As Long, _
       ByVal y As Long, ByVal cx As Long, ByVal cy As Long, _
       ByVal wFlags As Long) As Long
   
   ' Call SetWindowLong to instantiate the Window Procedure by passing the
   ' Address of MyWndProc.
   
   Public Sub NewWindowProc(fhWnd As Long)
      On Error Resume Next
      OldWndProc = SetWindowLong(fhWnd, GWL_WNDPROC, AddressOf MyWndProc)
   End Sub
   
   ' Once the Hook is in place, All messages will be processed by this
   ' function. Test for a WM_NOTIFY and parse the lParam to search for a
   ' specific value. In this case we are looking for EN_REQUESTRESIZE in the
   ' nmhdr structure. If an EN_REQUESTRESIZE is found then grab the next
   ' structure(REQSIZE) from the lParam.
   
   Public Function MyWndProc(ByVal hwnd As Long, _
                             ByVal Msg As Long, _
                             ByVal wParam As Long, _
                             ByVal lParam As Long) As Long
      On Error Resume Next
   
      Select Case Msg
         Case WM_NOTIFY
            Call CopyMemory(MaskHdr, ByVal lParam, Len(MaskHdr))
            
            If MaskHdr.code = EN_REQUESTRESIZE Then
               Call CopyMemory(rResize, ByVal lParam, Len(rResize))
   
   
               If rResize.rect.Bottom < gblHeight Then
                  Call SetWindowPos(RichWnd, VBNullPtr, _
                                    0, 0, gblWidth, _
                                    rResize.rect.Bottom, _
                                    SWP_SHOWWINDOW Or SWP_NOMOVE)
   
               Else
                  Call SetWindowPos(RichWnd, VBNullPtr, _
                                       0, 0, _
                                       gblWidth, gblHeight, _
                                       SWP_SHOWWINDOW Or SWP_NOMOVE)
               End If
   ' By modifying 2 of the above parameters you can create an endless bottom
   ' Richtext control. This may be desirable if you plan to wrap the control
   ' and use it on a web page. To test this, comment the 'If' Statement above
   ' and replace it with the SetWindowPos Function call below.
   ' The control will now Resize itself to its actual contents.
   
   '               Call SetWindowPos(RichWnd, VBNullPtr, _
   '                             0, 0, _
   '                             gblWidth, rResize.rect.Bottom, _
   '                             SWP_SHOWWINDOW Or SWP_NOMOVE)
            End If
               
         Case Else ' Handle other messages here.
      End Select
       
   ' Reset windowproc
      MyWndProc = CallWindowProc(OldWndProc, hwnd, Msg, wParam, lParam)
   
   End Function
   
   Public Sub ResetWindProc(hwnd As Long)
   
      On Error Resume Next
      
   ' Call SetWindowLong to remove the Windows Hook from app.
   
      Call SetWindowLong(hwnd, GWL_WNDPROC, OldWndProc)
   
   End Sub
   
   Public Sub SetMask(fhWnd As Long)
      On Error Resume Next
      Dim CurrentMask As Long
      Dim NewMask As Long
   ' Set the Event Mask to be called.
   
      CurrentMask = SendMessage(fhWnd, EM_GETEVENTMASK, 0, 0)
      NewMask = (CurrentMask Or ENM_REQUESTRESIZE)
      Call SendMessage(fhWnd, EM_SETEVENTMASK, 0, ENM_REQUESTRESIZE)
   End Sub
   					

8. Save and run the project. Note that the control is now being displayed using the height of the contents or the height of the form.
9. Comment out the If statement described in the comments in Module1 of the code sample, and uncomment the SetWindowPos function call following it.
10. Save the project and run it. The RichTextBox control now resizes itself to the height of its contents regardless of the size of the contents.