How To Manipulate Text Box Contents

MORE INFORMATION

This article assumes you are familiar with using the functions in the Windows API. The article will show you how to do the following:

• Determine the cursor position in a text box.
• Determine the line number of the line where your cursor is positioned in a multi-line text box.
• Determine the length of a selected line.
• Show all the text of a selected line.
• Insert text at a cursor position.

The first task uses a text box property. The remaining tasks use the SendMessage API function with the handle of the text box, a message, and the parameters required for that message.

To determine the cursor position in a text box, use the SelStart property of the text box. This property returns the position of the text relative to the first character of the first line. If you select a block of text, you can determine the cursor position by adding the SelLength property to the SelStart property.

The other three tasks require the SendMessage function with the Hwnd property of the text box, the appropriate message, and the required message parameters. The declaration of the SendMessage function is as follows:

   Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
      (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
      ByVal lParam As String) As Long
				

The following messages are used:

• EM_LINEFROMCHAR (&HC9)-returns the line number of the line where the cursor is positioned. Pass the cursor position with this message.
• EM_LINELENGTH (&HC1)-returns the length of the line where the cursor is positioned. Pass the cursor position with this message.
• EM_LINEINDEX (&HBB)-returns the number of characters in all the lines previous to the cursor position. Pass the results of the EM_LINEFROMCHAR message. Each line includes a carriage return and a line feed character.
• EM_GETLINECOUNT (&HBA)-returns the total number of lines in a multi-line text box.
• EM_GETLINE (&HC4)-returns the text of the line where the cursor is positioned. Pass the results of the EM_LINEFROMCHAR message.

The next section shows how to create a sample project that demonstrates how to manipulate text in a text box.

Steps to Create Sample Project

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.
2. Add a CommandButton, two Label controls and two Text boxes to Form1 and set the following properties to the appropriate controls:

      Control           Default Name     Property            Setting
      ---------------------------------------------------------------
      Text Box          Text1            MultiLine           True
   
      Label             Label1           AutoSize            True
   
   						

3. Copy the following code to the Code window of the Form1 form:

         Option Explicit
   
         Private Declare Function SendMessage Lib "user32" _
                                                Alias "SendMessageA" _
                                                (ByVal hwnd As Long, _
                                                ByVal wMsg As Long, _
                                                ByVal wParam As Long, _
                                                ByVal lParam As String) _
                                                As Long
   
         Private Const EM_GETLINE = &HC4
         Private Const EM_GETLINECOUNT = &HBA
         Private Const EM_LINEFROMCHAR = &HC9
         Private Const EM_LINEINDEX = &HBB
         Private Const EM_LINELENGTH = &HC1
         Private Const EM_REPLACESEL = &HC2
   
         Private Sub Form_Load()
            With Command1
               .Caption = "Insert This Text"
               .Height = 375
               .Left = 120
               .Top = 3000
               .Width = 1455
            End With
   
            With Form1
               .Caption = "Enhanced Text Box Sample Project"
               .Height = 4485
               .Width = 6990
            End With
   
            With Label1
               .Height = 195
               .Left = 120
               .Top = 240
               .Width = 3015
               .WordWrap = True
            End With
   
            With Label2
               .Height = 255
               .Left = 1800
               .Top = 3360
               .Width = 3135
            End With
   
            With Text1
               .Height = 2655
               .Left = 3360
               .Top = 240
               .Width = 3375
            End With
   
            With Text2
               .Height = 285
               .Left = 1680
               .Top = 3000
               .Width = 5055
            End With
   
         End Sub
   
         Private Sub Command1_Click()
            Call SendMessage(Text1.hwnd, EM_REPLACESEL, 0, Text2.Text)
            Label2.Caption = "Copied text is " + Text2.Text
            ShowInfo
         End Sub
   
         Private Sub Text1_KeyUp(KeyCode As Integer, Shift As Integer)
            ShowInfo
         End Sub
   
         Private Sub Text1_MouseMove(Button As Integer, _
                                       Shift As Integer, _
                                       X As Single, _
                                       Y As Single)
            ShowInfo
         End Sub
   
         Private Function ShowInfo()
         '********************************************************************
         ' Purpose:  Runs all the functions to get the necessary information
         '           in order to create the information text string. The text
         '           string is then displayed in the label control.
         '********************************************************************
   
            Dim strInfo As String
            Dim lCurPos As Long
            Dim lCurLineNum As Long, lTotLines As Long, lLineLength
            Dim lNumBChar As Long
            Dim sCurLine As String * 25
   
            'Determine Cursor Position
            If Text1.SelLength = 0 Then
               lCurPos = Text1.SelStart
            Else
               lCurPos = Text1.SelStart + Text1.SelLength
            End If
   
            'Determine Line Number
            lCurLineNum = SendMessage(Text1.hwnd, EM_LINEFROMCHAR, lCurPos, 0)
   
            'Determine the Line Length
            lLineLength = SendMessage(Text1.hwnd, EM_LINELENGTH, lCurPos, 0)
   
            'Determine the number of characters in lines before current
            'cursor position. Note that the number of characters includes a
            'carriage return and line feed characters at the end of each
            'line.
            lNumBChar = SendMessage(Text1.hwnd, EM_LINEINDEX, lCurLineNum, 0)
   
            'Determine Total number of lines
            lTotLines = SendMessage(Text1.hwnd, EM_GETLINECOUNT, 0, 0)
   
            'Determine Current Line
            sCurLine = Space(25)
            Call SendMessage(Text1.hwnd, EM_GETLINE, lCurLineNum, sCurLine)
   
            'Display the information
            strInfo = "Current Line: " + sCurLine + vbLf + _
                      "Line Length: " + CStr(lLineLength) + _
                      " Characters" + vbLf + _
                      "Line Number: " + CStr(lCurLineNum + 1) + _
                      " of " + CStr(lTotLines) + " Total Lines" + vbLf + _
                      "Cursor Position: " + CStr(lCurPos) + vbLf + _
                      "Total Characters in Previous Lines: " + _
                      CStr(lNumBChar) + vbLf + _
                      "Selected Length: " + CStr(Text1.SelLength) + vbLf + _
                      "Selected Text: " + Text1.SelText
   
            Label1.Caption = strInfo
   
         End Function
   						

4. On the Run menu, click Start or press the F5 key to start the program. Click inside the Text1 text box to display the text box information in Label1. To insert text into the Text1 text box, position the cursor in the Text1 text box where you want the text to be inserted. Enter the insertion text in the Text2 text box and click the CommandButton.

(c) Microsoft Corporation 1998, All Rights Reserved.
Contributions by Fred Nava, Microsoft Corporation


(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Arsenio Locsin, Microsoft Corporation