global variable in c#

kobystud · April 15th, 2004, 01:10 PM

hey,
i need help with c#.
i want to define a global variable that all classes know this variable without doing 'new' in every class where i want to use this variable.

this is my program - tell me whats wrong or what should i do? (pseudo code)

public class AA
{
    private static SqlConnection sqlCon;
    public AA()//constructor
    {
    sqlCon = new SqlConnection();
    sqlCon.ConnectionString = ".....";
    }

       public SqlConnection con2
    {
    get{return sqlCon;}
    set{SqlCon = value;}
    }

    }
}

when i try to use sqlCon in other classes there is an error:
"Object reference not set to an instance of an object"

class BB
{
AA a;
  public BB()//constructor
  {
   . . . .
  }

  void func1()
  {
   a.con2.open(); <----------- this is the error line
   ..........
   ..........
   }
}

thanking you in advance
koby

Imar · April 15th, 2004, 01:42 PM

Hi there,

That's because you only declared the private SqlConnection as static. You should change the public property con2 to static as well.

However, I am not so sure if this is a wise design decision. With this design, all classes that use AA (nice name, BTW ;) ) share *one* global connection object. I think this will result in poor performance, as all requests are queued up. If one of the classes that use AA open a DataReader, the connection is blocked until you close the reader.

A better approach is to have a public connection string that other classes can use. Alternatively, create a class that abstracts the data access code for you. e.g.:

Code:

public class MyDataClass()
{
  public DataSet ExecuteSQL(string sql)
  {
    string connectionString = AA.ConnectionString;
    // Create connection here with the ConnectionString from AA
    // return a dataset constructed with the connection created in
    // this method
  }
}

If you're trying to abstract your data access code from your UI or business layer, take a look here: http://msdn.microsoft.com/library/de...ml/daab-rm.asp
This is the Data Access Application Block from Microsoft and demonstrates a nice (and ready to use) way to implement a data access class.

HtH,

Imar
---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.
While typing this post, I was listening to: Pumpkin by Tricky (Track 5 from the album: Maxinquaye)

melvik · April 17th, 2004, 01:00 AM

take a look at this http://p2p.wrox.com/topic.asp?TOPIC_ID=2064.

HTH.

Always:),
Hovik Melkomian.

janeprime2001 · April 22nd, 2004, 05:56 AM

Hi there (hope this what you mean)

My connection string is stored in a public static string variable attached to my mainform. my mainform is declared public, so you can see all the form variables ans so forth. Then all you have to is SqlConnection cnfind = new SqlConnection(mdiMain.strConnectString);

This way you create a new connection and the danger of a deadlock is smaller

Hope it hels

jan

dude_in_africa