How to show database data in Textboxes?

Question

Hello! My scenario is as follows:

I am developing a web application in C# ASP.NET, and I am having some difficulties to bring the database data (via LINQ to SQL) to the page controls.

Below one of the controls of my file .aspx where I wish to bring a certain bank information

 <asp:TextBox 
    ID="txtCodigo" 
    ClientIDMode="Static" 
    CssClass="form-control"
    MaxLength="4"
    Enabled="false"
    runat="server">
 </asp:TextBox>

And down with mine .aspx.cs.

protected void Page_Load(object sender, EventArgs e)
    {            
            int idCliente;
            TB_CLIENTE_CLI cliente = new TB_CLIENTE_CLI();
            if (Int32.TryParse(Request.QueryString["ID"], out idCliente))
            {
                ClienteBusiness.ListarCliente(idCliente);

                txtCodigo.Text = cliente.ID_CLIENTE_CLI.ToString();
                txtRazaoSocial.Text = cliente.TXT_RAZAOSOCIAL_CLI;
                txtNomeFantasia.Text = cliente.TXT_NOMEFANTASIA_CLI;
                txtCNPJ.Text = cliente.TXT_CNPJ_CLI;
                txtCEP.Text = cliente.TXT_CEP_CLI;
                txtLogradouro.Text = cliente.TXT_LOGRADOURO_CLI;
            }

}

My application is divided into layers. The method ClienteBusiness.ListarCliente(idCliente) calls another method that, in turn, makes the query to the bank, as shown in the code below:

public static List<TB_CLIENTE_CLI> ListarCliente(int idCliente)
    {
        List<TB_CLIENTE_CLI> cliente = null;
        using (PlanoTesteDataContext context = new PlanoTesteDataContext())
        {
            cliente = (from clientes in context.TB_CLIENTE_CLIs
                       where clientes.ID_CLIENTE_CLI == idCliente
                       select clientes).ToList();
        }
        return cliente;
    }

Answer 1

There are some problems in your code:

1. In the Page_Load the command ClienteBusiness.ListarCliente(idCliente); does not populate the object cliente, since nothing receives the return of the métood listarCliente(...).
2. The method public static List<TB_CLIENTE_CLI> ListarCliente(int idCliente) returns a list while it should return only one client object, so that its code in the Page_Loadmake sense.

The line ClienteBusiness.ListarCliente(idCliente); in the method Page_Load should be: cliente = ClienteBusiness.ListarCliente(idCliente);.

The method public static List<TB_CLIENTE_CLI> ListarCliente(int idCliente) should be implemented as follows:

public static List<TB_CLIENTE_CLI> ListarCliente(int idCliente)
{
    List<TB_CLIENTE_CLI> cliente = null;
    using (PlanoTesteDataContext context = new PlanoTesteDataContext())
    {
        cliente = (from clientes in context.TB_CLIENTE_CLIs
                   where clientes.ID_CLIENTE_CLI == idCliente
                   select clientes).ToList();
    }
    return cliente.First();
}