TextBox.SelStart gives different value for mouse and keyboard - ms-access

Question

I have a TextBox on a Form. I take the cursor position using .SelStart property in that TextBox. It works as required when I click within TextBox. I then use that position to insert certain symbols on cursor position by pressing buttons on the same form which print their captions.
However, if I type some characters with the keyboard in TextBox, the Selstart returns 0. Even though I type several characters and cursor visibly is at the end of text, SelStart remains 0. Now, if I print buttons on other form the new characters get printed always at the start of TextBox which is not what I want. I want the captions to be printed always at cursor location even when I type with keyboard.
This behavior is very puzzling. Can someone help out on this?
Private LastPosition as Long 'declared in form module
Private sub t_LostFocus() 'to obtain last position in `TextBox`
LastPosition = Me!t.SelStart
End Sub
Private Sub Insert()
Dim Text As String
If LastPosition = 0 AND IsNull(Me!t.value) Then
Me!t.Value = " " + Me.ActiveControl.Caption
LastPosition = LastPosition + Len(Me.ActiveControl.Caption) + 1
ElseIf LastPosition >=0 AND Not IsNull(Me!t.Value) Then
Text = Me!t.Value
Me!t.Value = Left(Text, LastPosition) & " " & Me.ActiveControl.Caption & Mid (Text, LastPosition + 1)
LastPosition = LastPosition + Len(Me.ActiveControl.Caption)+1
Else
Me!t.Value = Me!t.Value + " " + Me.ActiveControl.Caption
End If
End Sub
Private Sub button1_Click()
Call Insert
End Sub

Answer 1

First a few facts about data entry on an Access Form. These need to be understood separately to properly explain the behavior described in the question, and especially if one is trying to alter the default behavior of the control.
The TextBox.SelStart, SelLength, and SelText are only available and valid when the control has focus. When a TextBox control receives focus again, the default is for all text to be selected, so that SelStart = 0 and SelLength = length of Text property. When using the mouse and clicking on the TextBox at a particular character position, the default behavior is bypassed and the cursor is placed at the mouse cursor, as expected.
TextBox controls have both a Text property and a Value property. The Text property represents the text string as it is displayed in the control. The displayed text can be different than the underlying value that the control represents, especially if Value is a non-text data type (e.g. an integer is stored as a number, but represented as individual text digits). The Value property returns a VBA variant which itself holds the underlying value of a particular data type.
For a bound control (i.e. the ControlSource property is populated), the Value data type will be the same as the bound source column.
For an unbound control (i.e. ControlSource is blank), the Value data type is dictated by the TextBox.Format property. If Format is blank, then the data type is text and will effectively match the Text property.
Text and Value are not always synced and this is especially true when the control has focus and is being edited. When the text is edited by the form user (i.e. not from code), Value is not updated until the control loses focus or Shift+Enter saves the form (except in cases when the Enter key behavior has been altered). Most events that will update the control will also involve clicking or otherwise moving focus outside the control, like saving the record, changing focus to another control, etc.
When the control’s Value is updated, the displayed text--accessible via the Text property--is interpreted and/or convert into the appropriate data type which is then saved to the Value property. (Sometimes the synchronization continues by reformatting the ‘Value’ back into a representation specified in the Format property. For instance, if Format = Long Date then: Text entered as “4-12-19” --> updated Value: #4/12/19 00:00# → updated Text: “Friday, April 12, 2019”.
One important last fact before I get to the point:
When TextBox.Value property is updated--even if it is also a String data type--the Text property is also refreshed and the cursor position and text selection is reset so that the entire text is selected. In other words, SelStart is set to 0 and SelLength is set to the length of Text, just like the behavior observed when the TextBox newly receives focus (as mentioned in the first point above).
Finally to the crux of all this detail:
When the keyboard is used to alter the text, this will eventually trigger an update, but usually not until the control loses focus. But when such an update occurs, it happens before the LostFocus event and the text selection is reset as described above, so that within the LostFocus event handler, SelStart == 0.
The issue is really not between keyboard and mouse, rather between the control text being altered or unaltered. If one only uses the arrow keys while in the textbox, then the cursor position and text selection are retained in the LostFocus event because a control update has not occurred. Contrariwise, if the mouse is used to alter the text (e.g. right-click Paste), this also triggers an update which will reset the selection. In fact, if one changes the text in any way and then uses the arrow keys or the mouse clicks, an update will still occur and reset the cursor position and text selection.
If the focus is moved outside the textbox and then back in using the mouse, an update may have occurred but the mouse will subsequently set the cursor position. I only mention this to be aware of stray clicks that might unknowing cause an update and still give the illusion that there is unique behavior to the mouse.
For kicks, press Shift+Enter to force an update but retain focus on the control, and observe that all of the text is automatically selected.
It is worth tracing the code by placing some "logging" statements in the various events, so that you can observe when they happen and the order.
Option Explicit
Option Compare Database
Dim LastSelStart As Integer
Dim LastSelLength As Integer
Dim UpdateSelStart As Integer
Dim UpdateSelLength As Integer
Private Sub button1_Click()
Insert
End Sub
Private Sub button2_Click()
Insert
End Sub
Private Sub Form_Load()
LastSelStart = -1
LastSelLength = 0
ResetUpdateSelValues
End Sub
Private Sub ResetUpdateSelValues()
UpdateSelStart = -1
UpdateSelLength = 0
End Sub
Private Sub t_AfterUpdate()
On Error Resume Next
UpdateSelStart = Me.t.SelStart
UpdateSelLength = Me.t.SelLength
If Err.Number <> 0 Then
UpdateSelStart = -1
End If
End Sub
Private Sub t_GotFocus()
On Error Resume Next
If LastSelStart >= 0 Then
Me.t.SelStart = LastSelStart
Me.t.SelLength = LastSelLength
End If
End Sub
Private Sub t_LostFocus()
LastSelStart = Me.t.SelStart
LastSelLength = Me.t.SelLength
If LastSelStart = 0 And UpdateSelStart > 0 Then
LastSelStart = UpdateSelStart
LastSelLength = UpdateSelLength
End If
ResetUpdateSelValues
End Sub
Private Sub Insert()
Dim caption As String
caption = Me.ActiveControl.caption
If IsNull(Me.t.Value) Then
Me.t.Value = caption
LastSelStart = Len(caption)
LastSelLength = 0
Else
Dim Text As String
Text = Me.t.Value
If LastSelStart = 0 Then
'* Don't add extra space at beginning
Text = caption & Mid(Text, LastSelLength + 1)
'Text = caption & Text
LastSelStart = Len(caption)
LastSelLength = 0
ElseIf LastSelStart > 0 Then
Text = Left(Text, LastSelStart) & " " & caption & Mid(Text, LastSelStart + LastSelLength + 1)
'Text = Left(Text, LastSelStart) & " " & caption & Mid(Text, LastSelStart + 0 + 1)
LastSelStart = LastSelStart + 1 + Len(caption)
LastSelLength = 0
Else
'If last cursor position is invalid, append characters
Text = Text & " " & caption
LastSelStart = Len(Text)
LastSelLength = 0
End If
t.Value = Text
End If
Me.t.SetFocus
End Sub