public variable. c#

The good solution from it_siege (http://www.experts-exchange.com/Programming/Languages/.NET/Q_28530111.html) uses arguments to pass cnString variable.

Question: Could you please revise this code to do it using a public variable?

namespace CodeSampleCS
{
    public partial class frmCS01 : Form
    {
        private string cnString = string.Empty;
        public frmCS01(string argument)
        {
            if (!string.IsNullOrEmpty(argument))
            {
                cnString = argument;
            }
            InitializeComponent();
        }

        private void frmCS01_Load(object sender, EventArgs e)
        {
            MessageBox.Show(string.Format("msg form{0}", !string.IsNullOrEmpty(cnString) ? string.Format(" - {0}", cnString) : "")); 
        }
    }
}
--------------------------------------------
namespace CodeSampleCS
{
    static class Program
    {
        public static string cnString = "";
        [STAThread]
        static void Main()
        {
            XmlTextReader xmlReader = new XmlTextReader("csNorthwind.xml");
            cnString = xmlReader.ReadElementString("connection");
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            MessageBox.Show("msg 1" + cnString);
            Application.Run(new frmCS01(cnString));
            MessageBox.Show("msg 2" + cnString);
        }
    }
}

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LVL 34
Mike EghtebasDatabase and Application DeveloperAsked:
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käµfm³d 👽Commented:
It should be exceedingly rare that you ever expose a variable (a.k.a. a field) publicly. Best practice is to create a public property that exposes the variable.

What is the goal here?
0
it_saigeDeveloperCommented:
To do it using a public variable (which is generally frowned upon) would take a couple of modifications (depended upon the way you wanted to do it -

1.  Using an instance variable passed as an argument:
namespace CodeSampleCS
{
    public partial class frmCS01 : Form
    {
        private Program caller = null;
        public frmCS01(Program argument)
        {
            if (argument != null)
                caller = argument;

            InitializeComponent();
        }

        private void frmCS01_Load(object sender, EventArgs e)
        {
            MessageBox.Show(string.Format("msg form{0}", !string.IsNullOrEmpty(caller.cnString) ? string.Format(" - {0}", caller.cnString) : "")); 
        }
    }
}
--------------------------------------------
namespace CodeSampleCS
{
    class Program
    {
        public string cnString = "";
        [STAThread]
        static void Main()
        {
            XmlTextReader xmlReader = new XmlTextReader("csNorthwind.xml");
            cnString = xmlReader.ReadElementString("connection");
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            MessageBox.Show("msg 1" + cnString);
            Application.Run(new frmCS01(this));
            MessageBox.Show("msg 2" + cnString);
        }
    }
}

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2.  Implement a globals class:
namespace CodeSampleCS
{
    public class Globals
    {
        private static string cnString = string.Empty;
        public static string ConnectionString
        {
            get { return cnString; }
            set 
            {
                if (!string.IsNullOrEmpty(value) && !value.Equals(cnString))
                    cnString = value;
            }
        }
    }
}

namespace CodeSampleCS
{
    public partial class frmCS01 : Form
    {
        public frmCS01()
        {
            InitializeComponent();
        }

        private void frmCS01_Load(object sender, EventArgs e)
        {
            MessageBox.Show(string.Format("msg form{0}", !string.IsNullOrEmpty(Globals.ConnectionString) ? string.Format(" - {0}", Globals.ConnectionString) : "")); 
        }
    }
}
--------------------------------------------
namespace CodeSampleCS
{
    static class Program
    {
        [STAThread]
        static void Main()
        {
            XmlTextReader xmlReader = new XmlTextReader("csNorthwind.xml");
            Globals.ConnectionString = xmlReader.ReadElementString("connection");
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            MessageBox.Show("msg 1" + Globals.ConnectionString);
            Application.Run(new frmCS01());
            MessageBox.Show("msg 2" + Globals.ConnectionString);
        }
    }
}

Open in new window


-saige-
0

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Mike EghtebasDatabase and Application DeveloperAuthor Commented:
kaufmed,

With vba background, having a global variable and using everywhere has its advantages.

I appreciate good comments and suggestion from both and follow it accordingly.

The current question is also good to know to be used when it is appropriate but not reading connection string.

I have a follow up question as to why cnString read from the xml file is different. I will post a link shortly.

Mike
0
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käµfm³d 👽Commented:
With vba background, having a global variable and using everywhere has its advantages.
Yes, that's typically the feeling of people who come from backgrounds where globals are prevalent. But as you program (object-oriented) more and more, and your programming becomes more advanced, you will begin to see how globals actually can do more harm that good. They especially make parallel programming difficult.
0
it_saigeDeveloperCommented:
Parrallel programming and threading are two examples of why I stated
which is generally frowned upon
@kaufmed - I just now realized that your avatar is not a pirate.  :D

-saige-
0
Mike EghtebasDatabase and Application DeveloperAuthor Commented:
0
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