Populate Some Data into textbox ASP.NET Web Form

Question

hi guys.. l'm try to popupate some data from database but always fail. I want if the btnAddCariAnggota click will show just nama_anggota not show all row in database. Any help could be appriaciate.

 

this is the tbl_anggota

CREATE TABLE [dbo].[tbl_anggota](
    [id_anggota] [varchar](50) NOT NULL,
    [nama_anggota] [varchar](50) NULL,
    [alamat] [varchar](350) NULL,
    [no_telpon] [varchar](50) NULL,
    [saldo] [bigint] NULL,
 CONSTRAINT [PK_tbl_anggota] PRIMARY KEY CLUSTERED
(
    [id_anggota] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

this is .aspx

<div class="col-md-6">
<div class="form-group">
<label for="id_anggota">
ID Anggota</label>
<div class="input-group">
<asp:TextBox ID="txtid_anggota" runat="server" CssClass="form-control" placeholder="Enter ID Anggota"></asp:TextBox>
<div class="input-group-append">
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button ID="btnAddCariAnggota" CssClass="btn btn-warning" runat="server" Text="Cari Data Anggota" OnClick="btnAddCariAnggota_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</div>
</div>
</div>
</div>
<div class="col-md-6">
<div class="form-group">
<label for="nama_anggota">
Nama Anggota</label>
<asp:TextBox ID="txtnama_anggota" runat="server" CssClass="form-control" placeholder="Enter Nama Anggota" ReadOnly="true"></asp:TextBox>
</div>
</div>

this code bihind

protected void btnCariAnggota_Click(object sender, EventArgs e)
    {
        using (SqlConnection con = new SqlConnection(koneksi))
        {
            using (SqlCommand sqlcmd = new SqlCommand("Select * from tbl_anggota where id_anggota='" + txtid_anggota.Text.Trim() + "'",con))
            {
                con.Open();
                sqlcmd.Connection = con;
                using (SqlDataReader rdr = sqlcmd.ExecuteReader())
                {
                    while (rdr.Read())
                    {
                        txtnama_anggota.Text = rdr["nama_anggota"].ToString();
                    }
                }
                con.Close();
            }
        }
    }