Column Type For Database-Retrieved Column : Windows Forms DataGridView Control

IT STUDENT 0

Hi. My issue is that related to the 3-tier Application development using ASP.NET (.NET Framework). As an IT student, I have been tasked to code for CRUD function using 3-tier.

For the Update functionality, I am facing an issue where for the row ' string tid = ((TextBox)row.Cells[0].Controls[0]).Text; ' it gives an error and I know that it is because of the '(TextBox)' part where you are supposed to input a Column Type for DataGridView. I do not understand how to resolve the issue since that column for me is retrieved from the database (a self-incremental primary key field 'PostID') and is not a 'TextBox' field unlike the other two mentioned columns. I do not know what to change the Column Type value to since those that I read about @ https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/column-types-in-the-windows-forms-datagridview-control?view=netframeworkdesktop-4.8 ('Column Types in the Windows Forms DataGridView Control' article) are not applicable in my case.

Pls advise if anyone knows the field type (column type) for a database-retrieved, unmodifiable column in DataGridView. (Pls refer to the code snippet below for reference) Thank you.

protected void gvPosts_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            PostsBLL pBLL = new PostsBLL();

            GridViewRow row = (GridViewRow)gvPosts.Rows[e.RowIndex];
            int id = int.Parse(gvPosts.DataKeys[e.RowIndex].Value.ToString());
            string tid = ((TextBox)row.Cells[0].Controls[0]).Text;
            string turgency = ((TextBox)row.Cells[3].Controls[0]).Text;
            string tdesc = ((TextBox)row.Cells[4].Controls[0]).Text;

            pBLL.PostUpdate(tid, turgency, tdesc);

            gvPosts.EditIndex = -1;
            bind();
        }

Lan Huang-MSFT 25,471 Reputation points Microsoft Vendor

2023-06-01T05:21:17.44+00:00

Hi @IT STUDENT,

I think you need to figure out whether your project is Windows Forms or ASP.NET Web Forms. Judging from the code you provided, you're using a GridView, which should be an ASP.NET Web Forms project.

But your question is about a Windows Forms project with a DataGridView.

I am facing an issue where for the row ' string tid = ((TextBox)row.Cells[0].Controls[0]).Text; ' it gives an error

You need to provide an error message, I guess it's a type conversion issue. Whether tid is int type, if yes, type conversion is required.

int tid = Convert.ToInt32(((TextBox)row.Cells[0].Controls[0]).Text.ToString());

Best regards,

Lan Huang
IT STUDENT 0 Reputation points

2023-06-07T08:34:55.18+00:00

Hello @Lan Huang-MSFT ,

Apologies for the delay in response, didn't check here for a reply (been having graded assessments 😢).

So, my project is ASP.NET Web Forms and yeah I'm using DataGridView to display retrieved data from my database, and this issue is when I'm coding for the update function where the ID is not something that the user is allowed to alter (since it a self-incremental primary key).

I found that bit of code from a practical exercise but it does not apply to my case (the ID field is a fixed field solely for relevant display, no edit) since mine is not a 'TextBox' and will not allow user input. Hence, I wish to enquire regarding what the column type really is then (an only display type) for my retrieve/display -only field.

For the error details it is a 'System.NullReferenceException' error. Once I access that particular laptop again will update here with the error message in full.

Thanks for the help!

Sincere Regards,

IT STUDENT :)

Lan Huang-MSFT 25,471 Microsoft Vendor

Hi @IT STUDENT,

I think I've explained it before. DataGridView is a winforms control, not a web control.

You cannot use the DataGridView control in ASP.NET Web Forms.

You'd better provide a minimal example that reproduces the problem so we can better help you with it.

What you're currently trying to achieve is retrieving data from a database? I think you can use Gridview.

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" AllowPaging="true">
                <Columns>
                    <asp:BoundField ItemStyle-Width="150px" DataField="ID" HeaderText="Customer ID" />
                    <asp:BoundField ItemStyle-Width="150px" DataField="Name" HeaderText="Contact Name" />
                    <asp:BoundField ItemStyle-Width="150px" DataField="disc" HeaderText="disc" />

                </Columns>
            </asp:GridView>
        </div>
    </form>
</body>
</html>

 protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                string constr = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
                using (SqlConnection con = new SqlConnection(constr))
                {
                    using (SqlCommand cmd = new SqlCommand("SELECT * FROM Table1"))
                    {
                        using (SqlDataAdapter sda = new SqlDataAdapter())
                        {
                            cmd.Connection = con;
                            sda.SelectCommand = cmd;
                            using (DataTable dt = new DataTable())
                            {
                                sda.Fill(dt);
                                GridView1.DataSource = dt;
                                GridView1.DataBind();
                            }
                        }
                    }
                }
            }
        }