Global variable

Often we want to use globals in ASP.NET. These do not need to be copied and only one is needed in the website application.

We use static properties (in the C# language) to store this single instance data. In testing, statics work well for global data.

First, older versions of ASP used the Application[] object, but this is inefficient in ASP.NET. To get started in adding your static global variables in ASP.NET, create the App_Code folder.

Then Right-click on your project name and select "Add ASP.NET Folder" and then App_Code. Here is the code you can put in the class file.

Detail The Global class is static. This means it is only created once for the type. You can name the class anything, not just Global.

Tip The class contains string types. Here we can have any value or reference type—not just string, but int, List or Dictionary.

Also It has a property. The "get" and "set" keywords mean you can access the field variable through the property.

using System;
using System.Data;
using System.Linq;
using System.Web;

/// <summary>
/// Contains my site's global variables.
/// </summary>
public static class Global
{
    /// <summary>
    /// Global variable storing important stuff.
    /// </summary>
    static string _importantData;

    /// <summary>
    /// Get or set the static important data.
    /// </summary>
    public static string ImportantData
    {
        get
        {
            return _importantData;
        }
        set
        {
            _importantData = value;
        }
    }
}

Example 2

Here we want to use the static global variables in the class. Open your web page's code-behind file. It is usually named Default.aspx.cs. This web form accesses the global variable.

And Page_Load first gets the static data. This example initializes the global variable if it isn't initialized yet.

Then It writes the value of Global.ImportantData to the literal. This is rendered to the browser.

using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // 1.
        // Get the current ImportantData.
        string important1 = Global.ImportantData;

        // 2.
        // If we don't have the data yet, initialize it.
        if (important1 == null)
        {
            // Example code.
            important1 = DateTime.Now.ToString();
            Global.ImportantData = important1;
        }

        // 3.
        // Render the important data.
        Important1.Text = important1;
    }
}

Discussion

Now run your web page and you will see that the global variable is used. This global data will only be run once for your entire application, saving lots of resources.

Note Static fields and properties in ASP.NET are always global. Another copy is never created. You will not have duplication.

Note 2 Static fields are efficient in normal situations. You will only have one copy of the data and there is no locking required.

Also The Application collection can be used the same way as static variables. But it may be slower and harder to deal with.

Tip With static fields, casting is not required. A problem with the Application object in ASP.NET is that it requires casting.

Note, startup

You can initialize the class at startup—put the code in the Application_Start event in Global.asax. Alternatively, use logic to lazily initialize the class.

We used static classes and variables to store site-wide objects in memory. This is a recommended practice. Static variables can make code easier to read and more robust.