Why Do My Static Variables in ASP.NET Get Reset, Even With an Active Session?

Understanding Static Variable Lifecycles in ASP.NET

In ASP.NET, static variables declared within a page class (outside Global.asax) and initialized in Page_Load sometimes reset unexpectedly, even with an active session. This behavior stems from the nature of static variables and ASP.NET's dynamic compilation.

Why Static Variables Reset

ASP.NET static variables exist for the application domain's lifespan. They are reset when the app domain restarts or the containing class is replaced. Since ASPX pages are dynamically compiled, ASP.NET might recompile the page class, effectively creating a new instance and resetting static variables.

Preventing Static Variable Loss During Class Replacement

While app domain restarts inevitably reset static variables, you can mitigate loss from class replacement. The solution is to relocate static variables from ASPX pages and the App_Code directory. A separate, static class within a different application module is recommended.

Important Considerations

Keep in mind that static variables are per application pool. Multi-pool deployments will have separate sets of static variables. Also, static variables aren't inherently thread-safe, requiring explicit synchronization mechanisms for multi-threaded access.

Alternatives to Static Variables in ASP.NET

For more reliable data persistence, consider alternatives to static variables if their reset is problematic. Databases with custom classes provide persistent storage, while Session State offers per-user data persistence. Avoid Application State as it's also memory-resident and lost on app domain restarts.

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