C# and Variable Scope in Winforms

Question

Within a Winform app, I would like data in an instantiated class to be accessible by multiple form controls.

For example, if I create Class Foo, which has a string property of name, I'd like to instantiate Foo a = new a() by clicking Button1, and when I click Button2, I'd like to be able to MessageBox.Show(a.name). There may be multiple instances of Foo, if that matters at all.

What is my best option for being able to use class instances in such a way?

Answer 1

Jon Skeet [C# MVP] Guest Posts: n/a

2: May 15 '07

re: Application variables in csharp.

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On May 15, 12:04 pm, Control Freq wrote: Quote: Still new to csharp. I am coming from a C++ background. > In C++ I would create a few top level variables in the application class. These are effectively global variables which can be accessed throughout the application because the application object is known. > What is the csharp equivalent of this practice? I can't seem to add variables to the "public class Program" class and get access to them from other files. > I am probably missing something obvious. Basically you want public static fields (or preferably properties).

An alternative to this is a singleton: http://pobox.com/~skeet/csharp/singleton.html

Jon

When in doubt, find something signed by John Skeet. Found on: http://bytes.com/topic/c-sharp/answers/646865-application-variables-csharp

Answer 2

A private field or property of a class satisfies the requirement - such field can be accessed by all methods of the class.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace Test
{
    public partial class Form1 : Form
    {
        foo a;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            a = new foo();
            a.name = "bar";
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (a != null && a.name != null)
                MessageBox.Show(a.name);
            else 
                MessageBox.Show("");
        }
    }

    public class foo
    {
        public string name { get; set; }

        public foo() { }
    }
}

If you want this variable to be accessible to other forms you'd need to make it public (preferably as property) - C# winform: Accessing public properties from other forms & difference between static and public properties

Answer 3

Winforms are nothing but some graphical elements backed by code. The code can own/create objects just like regular 'non-winform' code. The same scoping rules apply.

My guess if yours is more a problem of 'how does my form access shared state defined outside of it'? Create a static class, or have a setter on the class of your form that other code can use to set this shared state.

Answer 4

maybe you just want a static class

Answer 5

A form you create is just another class, derived from Form. A class exists in a given namespace, so you just need to create your Foo class in a namespace shared by your application's forms.

If a class is shared by multiple forms, then usually you'd separate out that class into a separate file.