Get error when set datasource for DropDownList in Gridview by using code behind

Question

I have a GridView to display my products and i have also made EditButton and DeleteButton to Update and Delete my products in the GridView. When I click on EditButton my gridview have a DropDownList to display my ProductType but i get an error with this message:

object reference not set to an instance of an object

This picture will show where i get that error:

And this is my method i use to fill datasource for my DropDownList:

Thank you for your help!

<asp:GridView ID="gridviewSanPham" runat="server" DataKeyNames="ID" AllowPaging="True" PageSize="4" AutoGenerateColumns="False" OnPageIndexChanging="gridviewSanPham_PageIndexChanging" OnRowCancelingEdit="gridviewSanPham_RowCancelingEdit" OnRowDeleting="gridviewSanPham_RowDeleting" OnRowEditing="gridviewSanPham_RowEditing" OnRowUpdating="gridviewSanPham_RowUpdating" OnRowDataBound="gridviewSanPham_RowDataBound">
        <Columns>
            <asp:CommandField ButtonType="Button" ShowEditButton="true" ShowCancelButton="true" />
            <asp:CommandField ButtonType="Button" ShowDeleteButton="true" ShowCancelButton="true" />
            <asp:BoundField DataField="ID" HeaderText="Mã sản phẩm" ReadOnly="true"/>

            <asp:TemplateField HeaderText="Mã Loại">
                <ItemTemplate>
                    <%# Eval("TypeID") %>
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:Label runat="server" ID="lblTypeID" Text='<%# Eval("TypeID") %>'></asp:Label>
                    <asp:DropDownList runat="server" ID="cboTypeID" ></asp:DropDownList> 
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Tên SP">
                <ItemTemplate>
                    <%# Eval("Name") %>
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:TextBox runat="server" ID="txtName" Text='<%# Eval("Name") %>'></asp:TextBox>
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Giá">
                <ItemTemplate>
                    <%# Eval("Price") %>
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:TextBox runat="server" ID="txtPrice" Text='<%# Eval("Price") %>'></asp:TextBox>
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Mô tả">
                <ItemTemplate>
                    <%# Eval("Description") %>
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:TextBox runat="server" ID="txtDescription" Text='<%# Eval("Description") %>'></asp:TextBox>
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Hình"> 
                <ItemTemplate>
                    <%# Eval("Image") %>
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:Label runat="server" ID="lblImage" Text='<%# Eval("Image") %>'></asp:Label>
                    <asp:FileUpload runat="server" ID="uploadImage" />
                </EditItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>

That is my aspx code

Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Suprabhat Biswal, Jul 18 '17 at 07:41
Can you also add a screen shot to show the values that come up your `SqlDataAdapter` object `da` — praty, Jul 18 '17 at 07:42
Please share your gridview html mark-up and FillLoaIsp code. This will help us identifying root cause. — Suprabhat Biswal, Jul 18 '17 at 07:44
Are you giving the correct dropdown ID in FindControl("cboTypeID") as from name it looks like you are giving checkbox ID in this. Can you share your gridview HTML? — Aman Sahni, Jul 18 '17 at 07:49
@Prabhat Yes i gave my Picture to show my FillLoaiSP method in my question — binh nguyen, Jul 18 '17 at 08:05
@AmanSahni Yes the ID in FindControl("cboTypeID") is correct — binh nguyen, Jul 18 '17 at 08:06

score 0 · Accepted Answer · 2017-07-18T08:28:01.843

0

Put your Dopdownlist binding code in if ((e.Row.RowState & DataControlRowState.Edit) > 0) in RowDataBound event:

protected void gridviewSanPham_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        // check if dropdownlist in edittemplate
        if ((e.Row.RowState & DataControlRowState.Edit) > 0)
        {
           DropDownList drop = (DropDownList)e.Row.FindControl("cboTypeID");

           drop.DataSource = FillLoaiSP();
           drop.DataBind();
        }
    }
 }

edited Jul 18 '17 at 08:28

answered Jul 18 '17 at 08:13

Thank you for your help. I will try it – binh nguyen Jul 18 '17 at 09:24
1

Thank you so much for your help. You made my day. I did like your code and my problem has been solved. – binh nguyen Jul 18 '17 at 10:22

score -1 · Answer 2 · edited Jul 18 '17 at 12:49

It will always throw an error because you are trying to find the dropdown in thegridviewSanPham_RowDataBound method. Just try to find the dropdown in the gridviewSanPham_RowEditing method. Because in RowDataBound event it will iterate through all rows, including the header and footer also, so it will throw a null object reference error in the case of the header and footer row.

Also your dropdown will be there in case of edit operation so either you can put filters for datarow and operation in the gridviewSanPham_RowDataBound method. But it's highly recommended that you bind the dropdown in the gridviewSanPham_RowEditing method.

Thank you for your help. I will try it. – binh nguyen Jul 18 '17 at 09:23 — binh nguyen, Jul 18 '17 at 09:23

Get error when set datasource for DropDownList in Gridview by using code behind

2 Answers2