对象引用未设置为对象的实例。（C＃Web应用程序）

Question

Please Help Me...from last two days I am facing this issue

My Connection class

public class Connection
{
    SqlConnection conn;
    SqlCommand cmd;

    public void connclose()
    {
        conn.Close();
    }

    public Connection()
    {
        SqlConnection conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");
        SqlCommand cmd = null;
    }

    public void nonquery(string qry)
    {
        conn.Open();
        cmd = new SqlCommand(qry, conn);
        cmd.ExecuteNonQuery();
        conn.Close();
    }
}

My Class

public class Master
{
    Connection conn = new Connection();

    public void insert(string name, string place, string company, string post)
    {
        string qry = "insert into company values('" + name + "','" + place + "','" + company + "'.'" + post + "')";
        conn.nonquery(qry);
    }
}

Am not asking you to debug code for me...please just point what is the error..I am a beginner so please..

Answer 1

The problem here is that you are trying to instantiate fields of your Connection class in a constructor but instead of it creating a local variables. So in terms of scope you are hiding your conn and cmd variables.

Try this:

public Connection()
{
    conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");
    cmd = null;
}

Answer 2

try this code

public class Connection
{
    SqlConnection conn;
    SqlCommand cmd;

    public void connclose()
    {
        conn.Close();
    }

    public Connection()
    {
        // initializing global variables
        conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");
        cmd = null;
    }

    public void nonquery(string qry)
    {
        conn.Open();
        cmd = new SqlCommand(qry, conn);
        cmd.ExecuteNonQuery();
        conn.Close();
    }
}

Answer 3

Although answer has been selected (which exactly solves the issue here) but still I would like to post my answer which uses SqlCommand Parameters.

public class Connection
{
   SqlConnection conn;
   SqlCommand cmd;

   public void connclose()
   {
     conn.Close();
   }

   public Connection()
   {   
       conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");        
       cmd = null;
   }

   public void nonquery(string qry, string[] arrParams, string[] arrParamsVals)
   {          
      try
      {
          conn.Open();
          cmd = new SqlCommand(qry, conn);

          for(int i=0; i < arrParams.Length; i++)
             cmd.Paratmeters.AddWithValue(arrParams[i], arrParamsVals[i]);

          cmd.ExecuteNonQuery();

      }
      catch{}
      finally { conn.Close(); }          
   }
 }

Master Class :

public class Master
{
    Connection conn = new Connection();

    public void insert(string name, string place, string company, string post)
    {
       string qry = "Insert into company values(@name, @place, @company, @post)";
       string[] arrParams= {"@name", "@place", "@company", "@post"};
       string[] arrParamsVals= {name, place, company, post};
       conn.nonquery(qry, arrParams, arrParamsVals);
    }
 }