Null Reference error when calling a Methode

Question

User1600235305 posted

I have a method called NewBatch_GetAndSetBatchID.

When I call this methode in the Page_Load methode it works perfectly.

But when I call this methode from a button (on the same page), I get:

Null reference exeption Object reference not set to an instance of an object.

It throws an error at:

BatchNoTextBox.Text = (batchID += 1).ToString();

When I debug, I can see that my batchID is filled with a value, somehow my BatchNoTextBox = null but I can't understand why.

This is my code:

        public void NewBatch_GetAndSetBatchID()
        {
            FormView1.ChangeMode(FormViewMode.Insert);

            
            string connectionString = ConfigurationManager.ConnectionStrings["DBConnection"].ConnectionString;
            try
            {
                using (SqlConnection conn = new SqlConnection(connectionString))
                {
                    SqlCommand sqlCommando = new SqlCommand("SELECT MAX(BatchNo) FROM BM_BrewBatchHeader", conn);

                    try
                    {
                        conn.Open();
                        batchID = Convert.ToInt32(sqlCommando.ExecuteScalar());
                    }
                    catch (Exception)
                    {

                    }
                    finally
                    {
                        conn.Close();
                    }
                }
            }
            catch (SqlException error)
            {

            }

            try
            {

                TextBox BatchNoTextBox = (TextBox)FormView1.FindControl("BatchNoTextBox");
                BatchNoTextBox.Text = (batchID += 1).ToString();
            }
            catch (Exception)
            {
                throw;
            }
        }

Answer 1

User409696431 posted

Can you clarify, which is null, the value of BatchNoTextBox.Text, or the result of the FindControl?

Answer 2

User1600235305 posted

TextBox BatchNoTextBox = (TextBox)FormView1.FindControl("BatchNoTextBox");
batchNoTextBox.Text = (batchID += 1).ToString();

The TextBox BatchNoTextBox is null.
When I call the methode from the Page_Load the TextBox BatchNoTextBox is {System.Web.UI.WebControls.TextBox}

Answer 3

User1120430333 posted

Martapon

TextBox BatchNoTextBox = (TextBox)FormView1.FindControl("BatchNoTextBox");
batchNoTextBox.Text = (batchID += 1).ToString();

The TextBox BatchNoTextBox is null.
When I call the methode from the Page_Load the TextBox BatchNoTextBox is {System.Web.UI.WebControls.TextBox}

It didn't find the control. The control can have a different name at the time you are trying to find the control. You should use the F12 Developer tool with the DOM Element browser and click on the control to show the actual name that it has at the time your program is trying to find it, if it's even there.. 

Answer 4

User1600235305 posted

I Found the answer here: https://forums.asp.net/t/1227594.aspx?Accessing+the+TextBoxes+in+a+FormView+from+C+code+behind

Thanks for the help people.

When I use the PreRender event it works fine:

protected void FormView1_PreRender(object sender, EventArgs e)
        {
            // if the mode is Edit or Insert
            if (this.FormView1.CurrentMode == FormViewMode.Edit || this.FormView1.CurrentMode == FormViewMode.Insert)
            {
                TextBox BatchNoTextBox = (TextBox)FormView1.FindControl("BatchNoTextBox");
                BatchNoTextBox.Text = (batchID += 1).ToString();
            }
        }