为什么我的表单会回发，尽管有“必填字段验证不匹配”？

Question

问：

我的页面上有一个 RequiredFieldValidator ，当我单击（回发触发）按钮时，它会进行回发，尽管该字段未输入必填项！ 这种行为的原因是什么？

我的.aspx：

                       <asp:UpdatePanel ID="UpdatePanel2" runat="server">
                            <Triggers>
                                <asp:PostBackTrigger ControlID="btn_Search" />
                            </Triggers>
                            <ContentTemplate>
                                <asp:ImageButton ID="btn_Search" runat="server" ImageUrl="~/Images/save.png" 
                                    OnClick="btn_Search_Click" OnClientClick="return postbackButtonClick();" />
                            </ContentTemplate>
                        </asp:UpdatePanel>

---

                     <asp:DropDownList ID="ddl_department" runat="server" Width="200px" OnSelectedIndexChanged="ddl_department_SelectedIndexChanged"
                            AutoPostBack="True">
                        </asp:DropDownList>
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="ddl_department"
                            Display="Dynamic" ErrorMessage="*" InitialValue="-1"></asp:RequiredFieldValidator>

                        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                            <ContentTemplate>
                                <asp:DropDownList ID="ddl_study" runat="server" Width="200px">
                                </asp:DropDownList>
                                <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="ddl_study"
                                    Display="Dynamic" ErrorMessage="*" InitialValue="-1"></asp:RequiredFieldValidator>
                            </ContentTemplate>
                            <Triggers>
                                <asp:AsyncPostBackTrigger ControlID="ddl_department" EventName="SelectedIndexChanged" />
                            </Triggers>
                        </asp:UpdatePanel>

---

                        <script type="text/javascript">
                            var updateProgress = null;
                            function postbackButtonClick() {
                                updateProgress = $find("<%= UpdateProgress1.ClientID %>");
                                window.setTimeout("updateProgress.set_visible(true)", updateProgress.get_displayAfter());
                                return true;
                            }
                        </script>

Answer 1

从 LinkBut​​ton 的 OnClientClick 属性值中删除 return 子句：OnClientClick="postbackButtonClick()" 并重写 postbackButtonClick 如下：

function postbackButtonClick() {
     Page_ClientValidate();

     if (Page_IsValid) {
          updateProgress = $find("<%= UpdateProgress1.ClientID %>");
          window.setTimeout("updateProgress.set_visible(true)", updateProgress.get_displayAfter());
          return true;
     }
}