[Solved] DropDownList SelectedValue Error: Object reference not set to an instance of an object

Hi Vincenzo67,

Use GridView OnRowDataBound event to set the DropDownList selected value based on the column value.

Refer below sample. I have used temporary DataTable for binding the GridView. You need to replace the binding code with your MySql client code.

HTML

<asp:GridView ID="gvProducts3" runat="server" DataKeyNames="ID" EnableViewState="true"
    CssClass="mGrid" HorizontalAlign="Center" OnRowDataBound="gvProducts3_RowDataBound"
    AutoGenerateColumns="false" Width="100%">
    <AlternatingRowStyle CssClass="altrows" />
    <Columns>
        <asp:TemplateField HeaderText="DDL" ItemStyle-CssClass="ddl_Class_new"
            ItemStyle-HorizontalAlign="Center">
            <ItemTemplate>
                <div>
                    <asp:DropDownList ID="ddl_I" runat="server" AutoPostBack="true"
                        BackColor="Yellow" CssClass="ddl_Class_new">
                        <asp:ListItem Text="[ === === === ]" Value=""></asp:ListItem>
                        <asp:ListItem Text="OK" Value="OK"></asp:ListItem>
                        <asp:ListItem Text="KO" Value="KO"></asp:ListItem>
                    </asp:DropDownList>
                </div>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Namespaces

C#

using System.Data;

VB.Net

Imports System.Data

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    gvProducts3.DataSource = RetrieveProducts_reco3();
    gvProducts3.DataBind();
}

private DataTable RetrieveProducts_reco3()
{
    DataTable dt = new DataTable();
    dt.Columns.Add("ID");
    dt.Columns.Add("tMotiv");
    dt.Rows.Add(1, "OK");
    dt.Rows.Add(1, "KO");
    return dt;
}

protected void gvProducts3_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DataRowView dr = (DataRowView)e.Row.DataItem;
        DropDownList ddl_I = e.Row.FindControl("ddl_I") as DropDownList;
        if (ddl_I.Items.FindByValue(dr["tMotiv"].ToString()) != null)
        {
            ddl_I.Items.FindByValue(dr["tMotiv"].ToString()).Selected = true;
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    gvProducts3.DataSource = RetrieveProducts_reco3()
    gvProducts3.DataBind()
End Sub

Private Function RetrieveProducts_reco3() As DataTable
    Dim dt As DataTable = New DataTable()
    dt.Columns.Add("ID")
    dt.Columns.Add("tMotiv")
    dt.Rows.Add(1, "OK")
    dt.Rows.Add(1, "KO")
    Return dt
End Function

Protected Sub gvProducts3_RowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
    If e.Row.RowType = DataControlRowType.DataRow Then
        Dim dr As DataRowView = CType(e.Row.DataItem, DataRowView)
        Dim ddl_I As DropDownList = TryCast(e.Row.FindControl("ddl_I"), DropDownList)
        If ddl_I.Items.FindByValue(dr("tMotiv").ToString()) IsNot Nothing Then
            ddl_I.Items.FindByValue(dr("tMotiv").ToString()).Selected = True
        End If
    End If
End Sub

Screenshot