Custom MsgBox via UserForm, startup position and resizable

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Just an observation ... there is an error message on this line :

msg = ActiveSheet.Shapes("Text Box 1").TextFrame.Characters.Text

I don't get that error. Perhaps something like ThisWorkbook.Worksheets("TheSheetName")... would work better.

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I am not certain what control is presently located on Sheet1 ... that is named "Textbox 1" .... but it isn't a textbox.

After inserting an ActiveX textbox onto the sheet and adding some text, the userform does load but is only displaying
an OK button.

???

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Disregard the last comment re: only displaying an OK button.

It is working now after adding the ActiveX textbox.

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Also ... here is the edited code :

Option Explicit

Private Sub TestMsgBox()
    Dim btnStyle As VbMsgBoxStyle
    Dim resp As VbMsgBoxResult
    Dim msg As String
    
    'msg = Replace(Space(1024), " ", "M")
    msg = ActiveSheet.TextBox1.Text
    msg = "Number of characters = " & Len(msg) & vbCrLf & msg
    
    'btnStyle = vbAbortRetryIgnore
    btnStyle = Range("VbMsgBoxStyleSelectedValue")
    
    resp = CustMsgBox.ShowMsgBox(msg, btnStyle, 144)
    
    msg = CustMsgBox.ReturnVal_btnTxt(resp)
    MsgBox "You clicked """ & msg & """"
    

End Sub

Sub Button1_Click()
    TestMsgBox
End Sub

Nice job on your project ! Good addition to the Forum that others will find helpful.

Cheers.