Will I Need a Public Shared Variable Here? - vb.net

Question

I have this sub in one form of my program to calculate and display a total profit from my database:
Public Sub Profit()
Try
Using connection As New OleDbConnection(connectionstring)
connection.Open()
Dim Command As New OleDbCommand("SELECT SUM(Price) FROM ItemsSold", connection)
Dim command2 As New OleDbCommand("SELECT SUM(TotalCost) FROM Inventory", connection)
Dim Turnover As Double = Convert.ToDouble(Command.ExecuteScalar())
Dim Cost As Double = Convert.ToDouble(command2.ExecuteScalar())
Dim TotalProfit As Double = Turnover - Cost
lblProfit.Text = "Profit: £" & TotalProfit
lblProfit2.Text = "Profit: £" & TotalProfit
lblProfit3.Text = "Profit: £" & TotalProfit
lblProfit4.Text = "Profit: £" & TotalProfit
connection.Close()
End Using
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
Also, in a different form of the program, I am updating a database table with a value provided by the user. What I want to do, is add this input value to this profit that is displayed in the label in the Profit() sub.
How can I go about doing this? Would I need to somehow make this profit variable a public shared variable to be able to access it in my other form? Is there another way to just increase this value and display the new increased variable?

Answer 1

How does shared variable supposed to help you?
you should to split functions which works with data and which works with form. In other words, when you need display data, you call GetProfit, and when you need to update profit you call SetProfit(ByVal profit As Double). And then use them in your project.
Based on your code, I suppose it should looks something like that
Public Sub GetProfit()
Dim profit As Double
Try
Using connection As New OleDbConnection(connectionstring)
connection.Open()
Dim Command As New OleDbCommand("SELECT SUM(Price) FROM ItemsSold", connection)
Dim command2 As New OleDbCommand("SELECT SUM(TotalCost) FROM Inventory", connection)
Dim Turnover As Double = Convert.ToDouble(Command.ExecuteScalar())
Dim Cost As Double = Convert.ToDouble(command2.ExecuteScalar())
Dim TotalProfit As Double = Turnover - Cost
profit = TotalProfit
connection.Close()
End Using
Catch ex As Exception
MsgBox(ex.Message)
End Try
' Return the result
return profit
End Sub
And for update
Public Sub SetProfit(ByVal newProfit As Double)
Try
Using connection As New OleDbConnection(connectionstring)
connection.Open()
' Commands for updating data (just for example)
Dim Command As New OleDbCommand("UPDATE ItemsSold SET Price = " & newProfit)
connection.Close()
End Using
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
And then you when you dealing with your form you just do like this
Private Sub Form1_Load()
Label1.Text = GetProfit()
Label2.Text = GetProfit()
End Sub
When you need to update
Private Sub Button1_Click()
SetProfile(GetProfit() + 5)
End
It is not exactly production code, just for an example