[Solved] ASP.Net GridView Row Update not working on Button Click

You need to call the Button Click event instead of GridView OnRowUpdating event.

Refer updated code.

HTML

<div>
    <span class="style1"><strong>Dropdownlist in Gridview </strong></span>
    <br />
    <br />
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
        BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px"
        CellPadding="3" DataKeyNames="COMP_ID" GridLines="Vertical" 
        OnRowDataBound="GridView1_RowDataBound" OnSelectedIndexChanged="GridView1_SelectedIndexChanged">
        <AlternatingRowStyle BackColor="#DCDCDC" />
        <Columns>
            <asp:TemplateField HeaderText="COMP_ID">
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("COMP_ID") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Emloyee ID">
                <ItemTemplate>
                    <asp:Label ID="Label2" runat="server" Text='<%# Bind("EMP_ID") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="COMP_MESSAGE">
                <ItemTemplate>
                    <asp:Label ID="Label4" runat="server" Text='<%# Bind("COMP_MESSAGE") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="COMP_LODGE_DATE">
                <ItemTemplate>
                    <asp:Label ID="Label5" runat="server" Text='<%# Bind("COMP_LODGE_DATE") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="STATUS_NAME">
                <ItemTemplate>
                    <asp:DropDownList ID="DropDownList1" runat="server">
                    </asp:DropDownList>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Assign_to">
                <ItemTemplate>
                    <asp:DropDownList ID="DropDownList2" runat="server">
                    </asp:DropDownList>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Remark">
                <ItemTemplate>
                    <asp:TextBox ID="TextBox5" runat="server">
                    </asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:Button ID="Button1" Text="Update" runat="server" CommandName="Save" OnClick="Update" CommandArgument="<%# Container.DataItemIndex %>" />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:Button ID="Button2" Text="Closed" runat="server" CommandName="Closed" CommandArgument="<%# Container.DataItemIndex %>" />
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
        <FooterStyle BackColor="#CCCCCC" ForeColor="Black" />
        <HeaderStyle BackColor="#000084" Font-Bold="True" ForeColor="White" />
        <PagerStyle BackColor="#999999" ForeColor="Black" HorizontalAlign="Center" />
        <RowStyle BackColor="#EEEEEE" ForeColor="Black" />
        <SelectedRowStyle BackColor="#008A8C" Font-Bold="True" ForeColor="White" />
        <SortedAscendingCellStyle BackColor="#F1F1F1" />
        <SortedAscendingHeaderStyle BackColor="#0000A9" />
        <SortedDescendingCellStyle BackColor="#CAC9C9" />
        <SortedDescendingHeaderStyle BackColor="#000065" />
    </asp:GridView>
    <br />
    <br />
</div>

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        refreshdata();
    }
}

public void refreshdata()
{
    con.Open();
    SqlCommand cmd = new SqlCommand("select * from comp_box", con);
    SqlDataAdapter sda = new SqlDataAdapter(cmd);
    DataTable dt = new DataTable();
    sda.Fill(dt);
    con.Close();
    GridView1.DataSource = dt;
    GridView1.DataBind();
}

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        SqlConnection con = new SqlConnection(@"Data Source=(localdb)\Projects;Initial Catalog=ocms_admin;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False");
        DropDownList DropDownList1 = (e.Row.FindControl("DropDownList1") as DropDownList);
        SqlCommand cmd = new SqlCommand("select * from complaint_status", con);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        sda.Fill(dt);
        DropDownList1.DataSource = dt;
        DropDownList1.DataTextField = "STATUS_NAME";
        DropDownList1.DataValueField = "STATUS_NAME";
        DropDownList1.DataBind();
        DropDownList1.Items.Insert(0, new ListItem("--STATUS_NAME--", "0"));

        DropDownList DropDownList2 = (e.Row.FindControl("DropDownList2") as DropDownList);
        cmd = new SqlCommand("select * from Assign_to", con);
        sda = new SqlDataAdapter(cmd);
        dt = new DataTable();
        sda.Fill(dt);
        DropDownList1.DataSource = dt;
        DropDownList1.DataTextField = "STATUS_NAME";
        DropDownList1.DataValueField = "STATUS_NAME";
        DropDownList1.DataBind();
        DropDownList1.Items.Insert(0, new ListItem("--SELECT_NAME--", "0"));
    }
}

protected void Update(object sender, EventArgs e)
{
    GridViewRow row = (sender as Button).NamingContainer as GridViewRow;
    int COMP_ID = Convert.ToInt32(GridView1.DataKeys[Convert.ToInt32((sender as Button).CommandArgument)].Values[0]);
    string STATUS_ID = (row.FindControl("DropDownList1") as DropDownList).SelectedItem.Text;
    string ATTEND_BY = (row.FindControl("DropDownList2") as DropDownList).SelectedItem.Text;
    string remark = (row.FindControl("TextBox5") as TextBox).Text;
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("UPDATE comp_box SET STATUS_ID = @STATUS_ID, ATTEND_BY = @ATTEND_BY, REMARKS = @REMARKS WHERE COMP_ID = @COMP_ID"))
        {
            cmd.Parameters.AddWithValue("@STATUS_ID", STATUS_ID);
            cmd.Parameters.AddWithValue("@ATTEND_BY", ATTEND_BY);
            cmd.Parameters.AddWithValue("@COMP_ID", COMP_ID);
            cmd.Parameters.AddWithValue("@REMARKS", remark);
            cmd.Connection = con;
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
    GridView1.EditIndex = -1;
}
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{

}