C# TextBox.text returns null

Question

I am trying to make an editor for a webpage. However, whenever I try and access the text from my textboxes in a gridview, I receive the error "object reference not set to an instance of an object." My code is as follows.

 SqlConnection con = new SqlConnection(DatabaseClient.ConnectionString);
            try
            {
            int id = (int)CompoundTable.DataKeys[e.RowIndex].Value;



            TextBox name = CompoundTable.Rows[e.RowIndex].FindControl("name") as TextBox;
                TextBox cat = (TextBox)CompoundTable.Rows[e.RowIndex].FindControl("cation_quantity");
                TextBox catname = (TextBox)CompoundTable.Rows[e.RowIndex].FindControl("cation");
                TextBox an = (TextBox)CompoundTable.Rows[e.RowIndex].FindControl("anion");
                TextBox anName = (TextBox)CompoundTable.Rows[e.RowIndex].FindControl("anion_quantity");
                TextBox diff = (TextBox)CompoundTable.Rows[e.RowIndex].FindControl("difficulty_level");

                con.Open();
                SqlCommand command = new SqlCommand("UPDATE Compound SET compound_name='" + name.Text  + "' WHERE compound_name = @compound",con); //The line that the error is thrown.
                command.Parameters.Add("@compound", SqlDbType.NVarChar, CompoundName.Text.Trim().Length).Value = CompoundName.Text.Trim();
                command.ExecuteNonQuery();
                con.Close();


                CompoundTable.EditIndex = -1;
                BindGridView();
            }

<asp:GridView ID="CompoundTable" runat="server" AllowSorting="True" AllowPaging="True" AutoGenerateColumns="False" PageSize="20" OnSorting="CompoundTable_Sorting" OnPageIndexChanging="CompoundTable_PageIndexChanging" OnRowCancelingEdit="CompoundTable_CancelEdit" OnRowEditing="CompoundTable_Edit" OnRowUpdating="CompoundTable_Update" CellPadding="4">
                <Columns>
                    <asp:BoundField DataField="id" HeaderText="Compound" SortExpression="name" />
                    <asp:BoundField DataField="name" HeaderText="Compound" SortExpression="name" />
                    <asp:BoundField DataField="cation" HeaderText="Cation" SortExpression="cation" />
                    <asp:BoundField DataField="cation_quantity" HeaderText="Cation Quantity" SortExpression="cation" />
                    <asp:BoundField DataField="anion" HeaderText="Anion" SortExpression="anion" />
                    <asp:BoundField DataField="ANION_QUANTITY" HeaderText="Anion Quantity" SortExpression="anion" />
                    <asp:BoundField DataField="difficulty_level" HeaderText="Difficulty" SortExpression="difficulty_level" />
                    <asp:HyperLinkField DataNavigateUrlFields="compound_id" DataNavigateUrlFormatString="DeleteCompound.aspx?compound={0}" Text="Delete Compound" />
                     <asp:TemplateField>
            <ItemTemplate>
                <asp:LinkButton ID="LBEdit" runat="server"  CommandName="Edit" >Edit</asp:LinkButton>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:LinkButton ID="LBCancel" runat="server" CommandName="Cancel">Cancel</asp:LinkButton>
                <asp:LinkButton ID="LBUpdate" runat="server" CommandName="Update">Update</asp:LinkButton>
            </EditItemTemplate>
        </asp:TemplateField>
                </Columns>
            </asp:GridView>

Answer 1

Because your name.Text is null.

If your target is updating the object by clicking the button update, you could do it by doing the following simple way:

                protected void YourGridIdHere_RowCommand(object sender, GridViewCommandEventArgs e)
                {
                    // If multiple buttons are used in a GridView control, use the
                    // CommandName property to determine which button was clicked.
                    if(e.CommandName=="Your command in CommandName")
                    {
                      // Convert the row index stored in the CommandArgument
                      // property to an Integer.
                      int index = Convert.ToInt32(e.CommandArgument);

                      // Retrieve the row that contains the button clicked 
                      // by the user from the Rows collection.
                      GridViewRow row = YourGridIdHere.Rows[index];

                      // Get data from current selected row.    
                      int ID_COL = 0; 
                      TableCell wantedData = row.Cells[ID_COL];
                      string str = wantedData.Text;

                      // So on....
                }

In form html, you could run it by adding:

OnRowCommand="YourGridIdHere_RowCommand"

to your:

<asp:GridView ID="CompoundTable" runat="server" AllowSorting="True" AllowPaging="True" AutoGenerateColumns="False" PageSize="20" OnSorting="CompoundTable_Sorting" OnPageIndexChanging="CompoundTable_PageIndexChanging" OnRowCancelingEdit="CompoundTable_CancelEdit" OnRowEditing="CompoundTable_Edit" OnRowUpdating="CompoundTable_Update" CellPadding="4">

Answer 2

Look at what CompoundTable.Rows[e.RowIndex].FindControl("name") is returning. I don't know webforms too well, but a quick look at the docs shows that BoundField does not inherit from TextBox.

When you cast using as, if the cast fails, no exception is thrown, but the returned object is null. You are getting the exception when trying to access the property on the null object.