c# - The connection was not closed the connection's current state is open

Question

How to fix this problem; connection already closed in my function:

SqlConnection con=new SqlConnection(@"Here is My Connection");

public void run_runcommand(string query)   
{   

    try   
    {   
        con.Open();   
        SqlCommand cmd1 = new SqlCommand(query, con);   

        cmd1.ExecuteNonQuery();    
        con.Close();    
    }    
    catch (Exception ex) { throw ex; }                        
}    
//...
try       
{           
    string query="my query";           
    db.run_runcommand(query);          
}         
catch(Exception ex)            
{         
    MessageBox.Show(ex.Message);              
}

Answer 1

I assume that the error is raised on this line:

con.Open(); // InvalidOperationException if it's already open

since you're reusing a connection and you probably have not closed it last time.

You should always close a connection immediately as soon as you're finished with it, best by using the using-statement:

public void run_runcommand(string query)   
{
    using(var con = new SqlConnection(connectionString))
    using(var cmd = new SqlCommand(query, con))
    {
        con.Open();
        // ...
    }  // close not needed since dispose also closes the connection
}

Note that you should not use a Catch block just to rethrow an exception. If you don't do anything with it don't catch it at all. It would be even better to use throw; instead of throw ex; to keep the stack trace. https://stackoverflow.com/a/4761295/284240