declaring variables in a class

Question

User-1820614410 posted

What's the proper way to declare variables in a class? I've been doing something like:

'in a class
public shared teststring As String = "first"

'on a code behind
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
  response.write("Current: " & someclass.teststring & "<br/>")
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
  someclass.teststring = "hello world"
  response.write(someclass.teststring)
End Sub

with shared variables loading a second window or reloading the page (without clicking the button) renders the hello world string. so how do I declare variables in a class but make it per instance? Thanks

Answer 1

User-68639941 posted

hi,

 you have declared the variable as shared i.e

 only one copy of that variable is shared across the class objects, so whoever requesting this page all will share this variable, that means it will persist the changes of this variable across the request or users.

if you want to maintain a separate copy for each request then you can remove the "shared" keyword

hi , while accessing dont use ClassName i.e simple access teststring instead of someclass.teststring

Answer 2

User-1820614410 posted

yes I understand that but see:

so how do I declare variables in a class but make it per instance? Thanks

if I remove the shared keyword and try to access it from the page I get an error message

Answer 3

User-1184423958 posted

For this scenario, you must implement Singleton pattern. Singleton pattern ensures a class has only one instance and provide a global point of access to it.

public class MySingletonClass
    {
        #region constructor
        private static MySingletonClass instance = null;

        /// <summary>
        /// Gets the instance.
        /// </summary>
        /// <value>The instance.</value>
        public static MySingletonClass Instance
        {
            get
            {
                if (instance == null)
                    instance = new MySingletonClass();

                return instance;
            }
        }

        //Private constructor prevents the class from being created.
        private MySingletonClass()
        {
        }
        #endregion

	
	public teststring As String
}

Then, access your variable like this...

MySingletonClass.Instance.teststring = "Saravanan M"

 

 

Answer 4

User-573138384 posted

For that you need to create an instance of the object and access the variable from that instance.

Lets assume your class name is TestClass like shown below then

Public Class TestClass
    Public teststring As String = "first"
End Class

Create instance of that class and access public members like

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim someclass As New TestClass()
        Response.Write("Current: " & someclass.teststring & "<br/>")
    End Sub
    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim someclass As New TestClass()
        someclass.teststring = "hello world"
        Response.Write(someclass.teststring)
    End Sub

Answer 5

User-1820614410 posted

worked. thanks!