ASP.NET中的静态方法问题

Question

I have an issue with the static method in ASP.NET. I created the Singleton below. During the execution process I will call Context.getInstance() several times and I need the same context value. But, once I make another request (Get, Post, wherever) to the server I need a new context because my context is dependant from .NET HttpContext. But, unfortunately once I call getInstance for the first time the class never will be instantiated again.

Any ideas how I solve this problem?

public class Context
{
   private static Context _context = null;

   private Context()
   { ... }

   public static Context getInstance()
   {
       if (Context._context == null)
           _context = new Context();

       return _context;
   }
}

Answer 1

Get rid of your static variable and store it in HttpContext.Current.Items .

public static Context GetInstance()
{
    if (HttpContext.Current.Items["MyContext"] == null) 
    {
        HttpContext.Current.Items["MyContext"] = new Context();
    }
    return (Context)HttpContext.Current.Items["MyContext"];
}

Answer 2

If I understand you correctly, you need the context only in a single page request, correct? If so, the method above certainly won't work - the static will live for the life of the app domain. This lifetime can vary depending on a number of factors. I would start by creating a base page class (inheriting from the core ASP.NET Page class) and include a Context property on it. Since the page only "lives" for one request, that should work for you.

Answer 3

Another approach - I prefer using my own ThreadStatic variables (ala HttpContext.Current) rather than use the HttpContext Items collections simply because I think (an opinion) that it makes for cleaner code. YMMV.

public class Context
{
    [ThreadStatic()]
    private static Context _Context = null;

    private HttpContext _HttpContext = null;

    public Context()
    {
        _HttpContext = HttpContext.Current;
    }

    public static Context Current
    {
        if(_Context == null || 
           _HttpContext != _HttpContext.Current)
        {
            _Context = new Context();
        }
        return _Context;
    }
}

Answer 4

如果您的变量是静态的，那么所有用户都将访问同一变量，并且对该变量的任何更改将仅在Web应用程序的情况下影响所有用户，逻辑是当您将变量设为静态时，则在服务器上分配内存位置时分配此位置是所有用户共享该位置的唯一原因，因为它是静态的。