Why does unreachable code Detected error occur in C#?

Question

    public Boolean LogarUsuario(string Pnome, string Psenha)
    {
        using (OleDbConnection conexao = new OleDbConnection(Conexao.stringConn))
        {
            conexao.Open();
            cmd.CommandText = "SELECT * FROM Usuario WHERE Nome = ? AND Senha = ?";
            cmd.Connection = conexao;
            cmd.CommandType = CommandType.Text;
            cmd.Parameters.Add("@Nome", OleDbType.WChar).Value = Pnome;
            cmd.Parameters.Add("@Senha", OleDbType.WChar).Value = Psenha;

            OleDbDataReader reader = cmd.ExecuteReader();

            try
            {
                reader.Read();
                Nome = String.Format("{0}", reader[1]);
                return true;
            }
            catch (Exception)
            {

                return false;
            }
            conexao.Close();
        }
    }

Answer 1

Don’t worry, the connection will be closed by using. Good, because if it hadn’t been used, there would have been more serious problems with the code. I don’t know if you have other problems because I haven’t seen everything, I can only talk about this method in isolation.

The way I was making it was wrong because nothing can be executed after one return unconditional, which is the case of try-catch. So how can an execution be done after it’s already out of the method? Usually when you want to ensure that the execution is always done before exiting the method you can use a try-finally, which is exactly what the using makes for resources that need to be closed.

But something I find strange is the exception being responsible for determining whether the user can log in or not, it seems very wrong, or at least not robust, even more capturing Exception that in this case it is not only risky, it seems to be quite wrong, to be almost certain that something wrong will happen and cause undesirable faults. I would take this.

And wouldn’t wear Boolean This is not C# "real", prefer bool :)

Ideally the OleDbDataReader should be "protected" by using also. It suffers from the same connection problem, it is an external resource that needs to be closed.

Besides, I’m worried about the variable cmd not be declared within this method. There may be a reason for this, but I doubt it is the right one.

I will understand that the exception is being used to detect whether the user is logged in or not. If this is not the case you have no reason to take this exception and return the result.

I’ll put a shape that looks better:

public bool LogarUsuario(string Pnome, string Psenha) {
    using (var conexao = new OleDbConnection(Conexao.stringConn)) {
        conexao.Open();
        var cmd = new OleDbCommand("SELECT * FROM Usuario WHERE Nome = ? AND Senha = ?", conexao);
        cmd.Parameters.Add("@Nome", OleDbType.WChar).Value = Pnome;
        cmd.Parameters.Add("@Senha", OleDbType.WChar).Value = Psenha;
        using (OleDbDataReader reader = cmd.ExecuteReader()) {
            reader.Read();
            if (reader.HasRows) {
                Nome = reader[1];
            }
            return reader.HasRows;
        }
    }
}

I put in the Github for future reference.

Answer 2

This warning/error indicates that there is code that will never be executed regardless of the execution path.

Note that when the execution reaches the block try/catch, whether an exception is made or not, a return, it is therefore not possible to execute the line conexao.Close();.

It is also not necessary because the Oledbconnection is instantiated inside the block using, the compiler create the necessary code for it to be closed, whether or not there is an exception.