Question

I’m trying to pass a value from DetailsView to FormView but I always get an error: Object reference is not set to an instance of an object. Somehow it did pass a value and I could still perform an insert. Its my first time programming in C#. Any hep would be much appreciated!

Thanks in advance

Here I’ve attached a code behind. I think the prob here is that I dont have a null check so how can I add a null check?

using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class BookLending : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void FormView1_DataBound(object sender, EventArgs e)
        {
            if(FormView1.CurrentMode == FormViewMode.Insert && FormView1.Fin != null) 
            {
                TextBox bookid = FormView1.FindControl("bookidTextBox") as TextBox;
                bookid.Text = ((DataRowView)DetailsView1.DataItem)["bookid"].ToString();
            }
            {
                TextBox employee = FormView1.FindControl("EmployeeIDTextBox") as TextBox;
                employee.Text = ((DataRowView)DetailsView1.DataItem)["EmployeeID"].ToString();
            }
        }
    }
}

Answer 1

There are a few places you can check for null.

1) If your cast is incorrect:

TextBox bookid = FormView1.FindControl("bookidTextBox") as TextBox;
if (bookid != null)
    bookid.Text = ((DataRowView)DetailsView1.DataItem)["bookid"].ToString();

TextBox employee = FormView1.FindControl("EmployeeIDTextBox") as TextBox;
if (employee != null)
    employee.Text = ((DataRowView)DetailsView1.DataItem)["EmployeeID"].ToString();

2) If the controls don’t have values, ToString() will also throw the object null reference exception:

((DataRowView)DetailsView1.DataItem)["bookid"] != null
((DataRowView)DetailsView1.DataItem)["EmployeeID"] != null

In which line of your code is the exception thrown?