Ajaxtoolkit ConfirmButtonExtender 无法触发

    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <ContentTemplate>
            <asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
            Text="Button" PostBackUrl="~/testing2.aspx" />
            <asp:ConfirmButtonExtender ID="ConfirmButtonExtender1" runat="server"
            targetControlID="Button1" 
                ConfirmText="Are you sure you want to click this button" 
                ConfirmOnFormSubmit="True" /> 
            <asp:TextBox ID="TextBox1" runat="server" Height="25px"></asp:TextBox>
            <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
        </ContentTemplate>

我认为您缺少OnClientCancel属性。查看下面的工作示例。

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确保您的页面使用正确的母版页。这是一个有效的代码。

asp:Content ContentPlaceHolderID="SampleContent" Runat="Server">
<script type='text/javascript'>
    function cancelClick() {
        var label = $get('ctl00_SampleContent_Label1');
        label.innerHTML = 'You hit cancel in the Confirm dialog on ' + (new Date()).localeFormat("T") + '.';
    }
</script>
    <ajaxToolkit:ToolkitScriptManager runat="Server" EnablePartialRendering="true" ID="ScriptManager1" />
    <div class="demoarea">
        <div class="demoheading">ConfirmButton Demonstration</div>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                    <asp:LinkButton ID="LinkButton" runat="server" OnClick="Button_Click">Click Me</asp:LinkButton>
                    <ajaxToolkit:ConfirmButtonExtender ID="ConfirmButtonExtender1" runat="server" 
                        TargetControlID="LinkButton"
                        ConfirmText="Are you sure you want to click the LinkButton?" 
                        OnClientCancel="cancelClick" />
                    <br />
                    <br />
                    <asp:Button ID="Button" runat="server" Text="Click Me" OnClick="Button_Click" /><br />
                    <ajaxToolkit:ConfirmButtonExtender ID="ConfirmButtonExtender2" runat="server" 
                        TargetControlID="Button"
                        OnClientCancel="cancelClick"
                        DisplayModalPopupID="ModalPopupExtender1" />
                    <br />
                    <ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="Button" PopupControlID="PNL" OkControlID="ButtonOk" CancelControlID="ButtonCancel" BackgroundCssClass="modalBackground" />
                    <asp:Panel ID="PNL" runat="server" style="display:none; width:200px; background-color:White; border-width:2px; border-color:Black; border-style:solid; padding:20px;">
                        Are you sure you want to click the Button?
                        <br /><br />
                        <div style="text-align:right;">
                            <asp:Button ID="ButtonOk" runat="server" Text="OK" />
                            <asp:Button ID="ButtonCancel" runat="server" Text="Cancel" />
                        </div>
                    </asp:Panel>
                <asp:Label ID="Label1" runat="server" />
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>
</asp:Content>