How to load values in the combobox by the form load event C#

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I’m trying through this code:

private void frmAdicionarProdutos_Load(object sender, EventArgs e)
        {
             string serverName = "localhost";
             string port = "5432";
             string userName = "postgres";
             string password = "adm";
             string databaseName = "GE";
             NpgsqlConnection conn = null;
             string ConnString = null;

             ConnString = String.Format("Server={0};Port={1};User Id={2};Password={3};Database={4};",
                                           serverName, port, userName, password, databaseName);

            using (conn = new NpgsqlConnection(ConnString))
            {
                conn.Open();

                string cmdCarregar = String.Format("SELECT PRODUTOS.ID_PRODUTO, PRODUTOS.NOME, PRODUTOS.PRECO FROM PRODUTOS;");
                using (NpgsqlCommand cmd = new NpgsqlCommand(cmdCarregar, conn))
                {
                    NpgsqlDataReader dr = cmd.ExecuteReader();
                    DataTable dt = new DataTable();
                    dt.Load(dr);

                    cbProdutos.DisplayMember = "nome";
                    cbProdutos.ValueMember = "id_produto";
                    cbProdutos.DataSource = dt;
                    conn.Close();
                }     
            }
        }

At first I just want to test this way anyway, then implement by calling the bank class.

This code does not show anything in Combobox, I think I forgot something.. I would like to show: Product name + value of it (concatenated).

c#

  • Probably the query should be like this: string cmdCarregar = String.Format("SELECT ID_PRODUTO, NOME, PRECO FROM PRODUTOS;");

  • In the same, I tested the query in postgres and returned me what I needed, but the combobox shows nothing yet..

  • 2 points, 1 do not need to use String.Format . 2 as you yourself said you need concatenate the PRODUCTS.NAME, PRODUCTS.PRICE .

2 answers

0

I can only see one cause for trouble: you nay associated the method frmAdicionarProdutos_Load to the event Form.Load

this.Load += new System.EventHandler(this.frmAdicionarProdutos_Load);

I tested your code here and the combo loaded right.

  • I made this change too and didn’t load it anyway.. load I think you’re right.. because I went to the events and the only load you have was the one that implemented the code

  • Weird. I tested your code and it worked. I just made a change to the query to take advantage of a table I already had. My query looked like this: string cmdCarregar = String.Format("SELECT \"ID\", \"Descricao\" FROM \"SchemaTeste\".\"TabTeste\";");

  • Another detail: I’m using the Npgsql versão 3.2.5, You came to check if the code of your routine is running?

  • How can I verify this? It would be by Breakpoint but I don’t know how to use it in this case

  • I used them, and it turned out Items.Count = 0

  • Yeah, put a Breakpoint pressing F9 over a line within Function. If the execution is not interrupted, then your routine is not running.

  • So it’s running.. Just don’t give the return

  • Let’s go continue this discussion in chat.

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0

I believe it will work when adding Databind()

cbProdutos.DataBind();

Make sure it works.

private void frmAdicionarProdutos_Load(object sender, EventArgs e)
    {
         string serverName = "localhost";
         string port = "5432";
         string userName = "postgres";
         string password = "adm";
         string databaseName = "GE";
         NpgsqlConnection conn = null;
         string ConnString = null;

         ConnString = String.Format("Server={0};Port={1};User Id={2};Password={3};Database={4};",
                                       serverName, port, userName, password, databaseName);

        using (conn = new NpgsqlConnection(ConnString))
        {
            conn.Open();

            string cmdCarregar = String.Format("SELECT PRODUTOS.ID_PRODUTO, PRODUTOS.NOME, PRODUTOS.PRECO FROM PRODUTOS;");
            using (NpgsqlCommand cmd = new NpgsqlCommand(cmdCarregar, conn))
            {
                NpgsqlDataReader dr = cmd.ExecuteReader();
                DataTable dt = new DataTable();
                dt.Load(dr);

                cbProdutos.DisplayMember = "nome";
                cbProdutos.ValueMember = "id_produto";
                cbProdutos.DataSource = dt;
                cbProdutos.DataBind();
                conn.Close();
            }     
        }
    }

  • There’s no such thing for me .DataBind() only .DataBindinds but tested and did not load it anyway.

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