Question

I can not pass one value from one class to another, when i try, the value pass to 0 instead the value from the first class.

I have this: an method that will check if the person is in the database, and the variable IDautor will gain the id is on the database, it will enter in the if clauses then the array id2 in the position 1 will save the value from IDautor… I pretend to use that value in the class Artigo, but the value came always 0 and i don’t no why
Class Autor

    public bool Login(TextBox txtUser, TextBox txtPassword)

    {

        string utl, pass;

        try
        {
            utl = txtUser.Text;
            pass = txtPassword.Text;

            _Sql = "Select Count(IDAutor) From Autor Where uUser = @uUser and Pass = @Pass";

            SqlCommand cmd = new SqlCommand(_Sql, Conn);

            cmd.Parameters.Add("@uUser", SqlDbType.VarChar).Value = utl;
            cmd.Parameters.Add("@Pass", SqlDbType.VarChar).Value = pass;

            Conn.Open();

            IDautor = (int)cmd.ExecuteScalar();                
            if (IDautor > 0)
            {
                MessageBox.Show("Bem Vindo");                        
                Conn.Close();
                id2[1] = IDautor;
                return true;
            }
            else
            {
                MessageBox.Show("Tera que tentar de novo");
                Conn.Close();
                return false;
            }                
        }
        catch(Exception ex)
        {
            MessageBox.Show("ERRO Message: "+ ex);
            Conn.Close();
            return false;
        }
    }



public int[] id2 
    {
        get { return this.id2; }
    }

and in trying to save the value in array id2 and use that value in another class

Class Artigo

public string AddArtigo(string newArtigo)
   {
       if (newArtigo == null)
       {
           return "Nao selecionou o PDF desejado. Tente de novo";               
       }
       if (newArtigo != null)
       {
           using (FileStream st = new FileStream(newArtigo, FileMode.Open, FileAccess.Read))
           {
               SqlConnection Conn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Convidado1\Desktop\Aplicaçao C#\Aplicaçao\ITArtiConf\ITArtiConf\Database1.mdf;Integrated Security=True;User Instance=True");

               Autor au = new Autor();

               byte[] buffer = new byte[st.Length];
               st.Read(buffer, 0, (int)st.Length);
               st.Close();

               Conn.Open();
               SqlCommand cmd = Conn.CreateCommand();
               cmd.CommandText = "insert into Artigo (idAutor) values('" + au.id2[1] + "')";
               cmd.ExecuteNonQuery();
               Conn.Close();


               SqlCommand cmd1 = new SqlCommand("UPDATE SomeTable SET Artigo=@Artigo WHERE idAutor =" + au.id2[1], Conn);
               cmd1.Parameters.AddWithValue("@Artigo", buffer);
               Conn.Open();
               int i = cmd1.ExecuteNonQuery();
               Conn.Close();                   
           }
           return "Guardado";
       }

       return "Error";           
   }

the au.id2[1] become 0 instead the value on the other class.

Answer 1

The best way would be not to use Autor au = new Autor(); but rather to change the constructor of the Artigo to accept an Autor and save it or some properties as members of Artigo or to change the signature of AddArtigo to accept an Autor.

So, either:

Autor au = new Autor();    
au.Login(user, pass); // this should really accept strings and not TextBoxes...
Artigo art = new Artigo(au); // this saves id2[1] as a member somewhere
art.AddArtigo(newArtigo); // why does the Artigo class have an AddArtigo method?

or

Autor au = new Autor();    
au.Login(user, pass);    
Artigo art = new Artigo();
art.AddArtigo(newArtigo, au);

Either way, there are multiple little issues with your solution (from having an array id2, to a Login method accepting TextBoxes and an Artigo that adds itself, most likely that code would be better suited as part of the Artigo constructor).