ASP.NET：从C#代码隐藏显示警报

我有一个asp.net页面与c#代码隐藏.如果更改gridview对象的选定索引而不选择“确认”或“取消”,我正在尝试使代码隐藏显示“警报”.用于检测确认或取消的代码是否正在工作,但是我的信息不会显示. “Alert.Show”代码从： http://archive.devnewz.com/devnewz-3-20061129JavaScriptAlertShowmessagefromASPNETCodebehind.html借用.

例如,当从page_load()测试时,Alert.show工作正常,但不在我的selected_index_changed方法中.任何想法为什么？也许与如何实现Alert.Show()有关？

if (ChangeAttemptedId && !IsSavedId)
{
 Alert.Show("Dispatch assignment saved,but you forgot to click Confirm or Cancel!)");
}

ASP.NET代码：

<asp:Table ID="Table1" runat="server" CssClass="DefaultTable">
    <asp:TableRow runat="server">
        <asp:TableCell runat="server" Width="50%" VerticalAlign="Top" HorizontalAlign="Left">
            <asp:UpdatePanel ID="detailsUP" runat="server" UpdateMode="Always" ChildrenAsTriggers="True">
                <ContentTemplate>
                    <!--
                    <asp:Label ID="label1" runat="server" Text="Car To Dispatch: " CssClass="DefaultLabel"></asp:Label>
                    <asp:DropDownList ID="CarsDDL" runat="server" DataSourceID="VehiclesEDS" DataMember="CarNum" DataTextField="CarNum" AppendDataBoundItems="True" Font-Bold="True">
                        <asp:ListItem Selected="True" Text="-"></asp:ListItem>
                    </asp:DropDownList>
                    -->
                    <asp:DetailsView ID="RideToAssignDV" runat="server" Height="400px" 
                        Width="400px" AutoGenerateRows="False" 
                        BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px" 
                        CellPadding="3" GridLines="Vertical">
                        <AlternatingRowStyle BackColor="#DCDCDC" />
                        <EditRowStyle BackColor="#008A8C" Font-Bold="True" ForeColor="White" />
                        <Fields>
                            <asp:BoundField DataField="AssignedCar" HeaderText="Car" 
                                SortExpression="AssignedCar" NullDisplayText="---" />            
                            <asp:BoundField DataField="Name" HeaderText="Name" 
                                SortExpression="Name" NullDisplayText="---" />
                            <asp:BoundField DataField="Phone" HeaderText="Phone" 
                                SortExpression="Phone" NullDisplayText="---" />
                            <asp:BoundField DataField="NumPatrons" HeaderText="Size" 
                                SortExpression="NumPatrons" NullDisplayText="---" />                
                            <asp:BoundField DataField="PickupAddress" HeaderText="Pickup Address" 
                                SortExpression="PickupAddress" NullDisplayText="---" />
                            <asp:BoundField DataField="DropoffAddress" HeaderText="Drop-Off Address" 
                                SortExpression="DropoffAddress" NullDisplayText="---" />
                            <asp:BoundField DataField="CreatedBy" HeaderText="Created By" 
                                SortExpression="CreatedBy" NullDisplayText="---" />
                            <asp:BoundField DataField="TimeOfCall" HeaderText="Call Time" 
                                SortExpression="TimeOfCall" ReadOnly="True" NullDisplayText="---" />
                        </Fields>
                        <FooterStyle BackColor="#CCCCCC" ForeColor="Black" BorderStyle="Inset" BorderColor="#C6940D" HorizontalAlign="Center" Height="25px" />
                        <FooterTemplate>
                            <asp:Button ID="confirmButton" runat="server" Text="Confirm" ForeColor="Green" HorizontalAlign="Center" OnClick="confirmButton_Click"/>
                            <asp:Button ID="cancelButton" runat="server" Text="Cancel" ForeColor="Red" HorizontalAlign="Center" 
                                OnClick="cancelButton_Click" OnClientClick="displayTopTen();" />
                        </FooterTemplate>
                        <HeaderStyle BackColor="#004812" Font-Bold="True" />
                        <PagerStyle BackColor="#999999" ForeColor="Black" />
                        <RowStyle BackColor="#EEEEEE" ForeColor="Black" />                            
                    </asp:DetailsView>
                </ContentTemplate>
            </asp:UpdatePanel>
        </asp:TableCell>

        <asp:TableCell runat="server" Width="50%">
            <asp:UpdatePanel ID="mapUP" runat="server" UpdateMode="Conditional">
                <ContentTemplate>
                    <div id="map_canvas" style="height: 400px; width:400px;"></div>
                </ContentTemplate>
            </asp:UpdatePanel>
        </asp:TableCell>
    </asp:TableRow>
</asp:Table>

<br />
<asp:Label ID="GV_Label1" runat="server" Text="Car To Dispatch: " CssClass="DefaultLabel"></asp:Label>

<asp:UpdatePanel ID="SelectCarUP" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <asp:GridView ID="VehiclesGridView" runat="server" AllowPaging="True" 
            AllowSorting="True" DataSourceID="VehiclesEDS" AutoGenerateColumns="False" 
            onselectedindexchanged="VehiclesGridView_SelectedIndexChanged" 
            BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px" 
            CellPadding="3" GridLines="Vertical" ShowHeaderWhenEmpty="True" AutoPostBack="True">
            <AlternatingRowStyle BackColor="#DCDCDC" />
            <Columns>
                <asp:TemplateField ShowHeader="False">
                    <ItemTemplate>
                        <asp:LinkButton ID="GVSelectButton" runat="server" CausesValidation="False" 
                            CommandName="Select" Text="Select"></asp:LinkButton>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField DataField="CarNum" HeaderText="Car" ReadOnly="True" 
                    SortExpression="CarNum" />
                <asp:BoundField DataField="CurrPassengers" HeaderText="Passengers" 
                    ReadOnly="True" SortExpression="CurrPassengers" />
                <asp:BoundField DataField="MaxPassengers" HeaderText="Capacity" ReadOnly="True" 
                    SortExpression="MaxPassengers" />
                <asp:BoundField DataField="Status" HeaderText="Status" ReadOnly="True" 
                    SortExpression="Status" />
                <asp:BoundField DataField="StartAdd" HeaderText="Pick-Up Address" 
                    ReadOnly="True" SortExpression="StartAdd" />
                <asp:BoundField DataField="EndAdd" HeaderText="Drop-Off Address" 
                    ReadOnly="True" SortExpression="EndAdd" />
                <asp:BoundField DataField="AvgRideTime" HeaderText="Avg. Ride Time" 
                    ReadOnly="True" SortExpression="AvgRideTime" />
            </Columns>
            <FooterStyle BackColor="#CCCCCC" ForeColor="Black" />
            <HeaderStyle BackColor="#004812" Font-Bold="True" ForeColor="White" />
            <PagerStyle BackColor="#999999" ForeColor="Black" HorizontalAlign="Center" />
            <RowStyle BackColor="#EEEEEE" ForeColor="Black" />
            <SelectedRowStyle BackColor="#C6940D" Font-Bold="True" ForeColor="White" />
            <SortedAscendingCellStyle BackColor="#F1F1F1" />
            <SortedAscendingHeaderStyle BackColor="#C6940D" />
            <SortedDescendingCellStyle BackColor="#CAC9C9" />
            <SortedDescendingHeaderStyle BackColor="#9F770B" />
        </asp:GridView>
    </ContentTemplate>
</asp:UpdatePanel>

protected void Page_Load(object sender,EventArgs e)
{
    ScriptManager.RegisterStartupScript(this.Page,this.Page.GetType(),"err_msg","alert('Dispatch assignment saved,but you forgot to click Confirm or Cancel!)');",true);
}