Passing parameters by value - mysql

Question

To all, I am learning Visual Basic and I am currently working on a Windows Application. I have two text box methods (usernameTextBox, passwordTextBox). In which the user will enter data and then hit the submit button (Button1_Click). That method will call connect. What I want to be able to do, is to have the user type-in their username and password. Then it is passed by value, not reference into connect() when it is invoked inside the Button method.
Kind of like an authentication page. Now I have values in connect(FirstName:="JohnDoe", Password:="password") - this is basically for testing MySQL server and for demonstration of what I am trying to attempt.
Imports MySql.Data.MySqlClient
Public Class SecurePasswordList
Dim conn As New MySqlConnection
Public Sub connect(ByVal FirstName As String, ByVal Password As String)
Dim DatabaseName As String = "mysql"
Dim server As String = "10.1.0.0"
If Not conn Is Nothing Then conn.Close()
conn.ConnectionString = String.Format("server={0}; user id={1}; password={2}; database={3}; pooling=false", server, FirstName, Password, DatabaseName)
Try
conn.Open()
Catch ex As Exception
MsgBox(ex.Message)
End Try
conn.Close()
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
connect(FirstName:="JohnDoe", Password:="password")
End Sub
Private Sub SecurePasswordList_Load(sender As Object, e As EventArgs) Handles MyBase.Load
End Sub
Private Sub usernameTextBox_TextChanged(sender As Object, e As EventArgs) Handles usernameTextBox.TextChanged
Dim FirstName As String
FirstName = usernameTextBox.Text
End Sub
Private Sub passwordTextBox_TextChanged(sender As Object, e As EventArgs) Handles passwordTextBox.TextChanged
Dim Password As String
Password = passwordTextBox.Text
End Sub
End Class

Answer 1

Change
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
connect(FirstName:="JohnDoe", Password:="password")
End Sub
to
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
connect(FirstName, Password)
End Sub
but you should ensure that FirstName and Password are initialized AND held as class variables.
Move
Dim FirstName As String
Dim FirstName As String
to be in the class, not the event handling functions (Click etc). Like this:
Public Class SecurePasswordList
Dim conn As New MySqlConnection
Dim FirstName As String
Dim FirstName As String
BUT really you can redo your code like this (as all you want is the Text from the controls):
Imports MySql.Data.MySqlClient
Public Class SecurePasswordList
Dim conn As New MySqlConnection
Public Sub connect(ByVal FirstName As String, ByVal Password As String)
Dim DatabaseName As String = "mysql"
Dim server As String = "10.1.0.0"
If Not conn Is Nothing Then conn.Close()
conn.ConnectionString = String.Format("server={0}; user id={1}; password={2}; database={3}; pooling=false", server, FirstName, Password, DatabaseName)
Try
conn.Open()
Catch ex As Exception
MsgBox(ex.Message)
End Try
conn.Close()
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
connect(usernameTextBox.Text, passwordTextBox.Text)
End Sub
End Class
I dont think passing by value or reference is the issue here. Do you want the connect function to modify the strings passed into it? I doubt it. So in that case Value or reference is fine. Strings are passed by a copied instance by reference, so in effect they are passed by Value unless you use Byref in the function declaration which will. Every class (int, string, etc) are passed differently in VB by default. You need to check each type to know what it will do if you specify Byval or Byref. String creates a copy of the String if you use Byval, but is actually accessed using the pointer to the newly created String. So it depends how deep you want to dig too