Może to wyglądać mniej więcej tak 
, z zapisem stanu do pliku xml (który jest tworzony przy pierwszym uruchomieniu):
Imports System.IO
Imports System.Text
Imports System.Xml
Imports WindowsApplication1.ApplicationDataXml
Public Class Form1
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
End Sub
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
SetValueMonthly(TextBox1) ' Wartość domyslnie wzrośnie o 1 np.: TextBox1.Text += 1
' TextBox1.Name = Amount
' SetValueMonthly(Amount) ' itp.
' SetValueMonthly(TextBox1, 3) ' Wartość wzrośnie o 3 np.: TextBox1.text += 3
End Sub
Private Sub SetValueMonthly(ByRef TextBox As TextBox, Optional ByVal value As Integer = 1)
Try
Dim value_from_xml, value_date_from_xml As String
value_from_xml = GetValueFromXmlFile("monthly-value", "value")
value_date_from_xml = GetValueFromXmlFile("monthly-value", "date")
If String.IsNullOrEmpty(value_from_xml) Or String.IsNullOrEmpty(value_date_from_xml) Then
Throw New System.Exception("Nie mogę ustawić prawidłowej wartości dla: " & TextBox.Name)
Else
Dim textbox_value As Integer = Int32.Parse(value_from_xml)
Dim check_date As DateTime = Date.Parse(value_date_from_xml)
Dim check_date_interval As DateTime = check_date.AddMonths(1)
Dim check_date_today As DateTime = Today.ToString("d")
Dim date_compare As Integer = DateTime.Compare(check_date_today, check_date_interval)
If date_compare >= 0 Then ' Minął miesiąc
Dim textbox_value_computed As Integer = textbox_value + value
' Zapisanie nowych wartości do pliku xml
SetValueToXmlFile("monthly-value", "value", textbox_value_computed)
SetValueToXmlFile("monthly-value", "date", check_date_today)
TextBox.Text = textbox_value_computed
Else ' Nie minął miesiąc
TextBox.Text = textbox_value
End If
End If
Catch ex As Exception
MsgBox(ex.Message, MsgBoxStyle.OkOnly + MsgBoxStyle.Exclamation, "Wystąpił błąd")
End Try
End Sub
End Class
Module ApplicationDataXml
Private Const APP_DATA_FILE_NAME = "data.xml"
Private APP_PATH As String = Application.StartupPath()
Private APP_DATA_FILE_PATH As String = Path.Combine(APP_PATH, APP_DATA_FILE_NAME)
Public Function GetValueFromXmlFile(ByVal node_name As String, ByVal value_name As String) As String
Try
Dim return_value As String = String.Empty
If CreateAppDataXmlFile() Then
Dim oXMLDoc As New XmlDocument()
oXMLDoc.Load(APP_DATA_FILE_PATH)
Dim oNodes As XmlNodeList = oXMLDoc.DocumentElement.SelectNodes(node_name)
For Each oNode As XmlNode In oNodes
return_value = oNode.SelectSingleNode(value_name).InnerText
Next
End If
If String.IsNullOrEmpty(return_value) Then
Throw New System.Exception("Wartość o nazwie: " & value_name & " nie istnieje.")
End If
Return return_value
Catch ex As Exception
MsgBox("Nie mogę wczytać wartości: " & node_name & vbCrLf & _
"Z pliku: " & APP_DATA_FILE_NAME & vbCrLf & ex.Message,
MsgBoxStyle.OkOnly + MsgBoxStyle.Exclamation, "Wystąpił błąd")
Return String.Empty
End Try
End Function
Public Function SetValueToXmlFile(ByVal node_name As String, ByVal value_name As String, ByVal value As String) As Boolean
Try
If CreateAppDataXmlFile() Then
Dim oXMLDoc As New XmlDocument()
oXMLDoc.Load(APP_DATA_FILE_PATH)
Dim oNodes As XmlNodeList = oXMLDoc.DocumentElement.SelectNodes(node_name)
For Each oNode As XmlNode In oNodes
oNode.SelectSingleNode(value_name).InnerText = value
Next
oXMLDoc.Save(APP_DATA_FILE_PATH)
End If
Return True
Catch ex As Exception
MsgBox(ex.Message, MsgBoxStyle.OkOnly + MsgBoxStyle.Exclamation, "Wystąpił błąd")
Return False
End Try
End Function
Private Function CreateAppDataXmlFile(Optional ByVal overwrite As Boolean = False) As Boolean
Try
If Not File.Exists(APP_DATA_FILE_PATH) Or overwrite = True Then
' Pierwsze uruchomienie programu tworzenie pliku: APP_DATA_FILE_NAME
' Z począkowymi danymi.
Dim oXMLWriter As New XmlTextWriter(APP_DATA_FILE_PATH, Encoding.UTF8)
With oXMLWriter
.WriteStartDocument(True)
.Formatting = Formatting.Indented
.Indentation = 2
.WriteStartElement("root")
.WriteStartElement("monthly-value")
.WriteStartElement("value")
.WriteString("0") ' Wartość domyślna początkowa
.WriteEndElement()
.WriteStartElement("date")
.WriteString(Today.ToString("d")) ' Data w formie: 05.09.2020
.WriteEndElement()
.WriteEndElement() ' "/monthly-value"
.WriteFullEndElement()
.WriteEndDocument()
.Close()
' Zostaje zapisany plik xml o takiej strukturze
' <?xml version="1.0" encoding="utf-8" standalone="yes"?>
' <root>
' <monthly-value>
' <value>0</value>
' <date>05.09.2020</date>
' </monthly-value>
' </root>
End With
End If
' Przy kolejnych uruchomieniach, gdy plik istnieje ...
Return True ' ... można odczytać dane
Catch ex As Exception
MsgBox("Nie mogę utworzyć pliku: " & APP_DATA_FILE_NAME & vbCrLf & _
"W lokalizacji: " & APP_PATH, MsgBoxStyle.OkOnly + MsgBoxStyle.Exclamation, "Wystąpił błąd")
Return False
End Try
End Function
End Module
data.xml - widok
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<root>
<monthly-value>
<value>0</value>
<date>05.09.2020</date>
</monthly-value>
</root>
