C# UpdateProgress在图像上载后第二次不工作

UpdateProgress在btnSubmit单击时显示，但在我上载图像后的第二次中，UpdateProgress不会显示。如果我没有上传图像，则会显示更新进度。我还发现第二次上传图像后，内容占位符1\u updProgress从控制台中消失。否则（在第二次中没有图像上载）内容占位符1\u updProgress在控制台中。所以我认为问题在于第二次上传的图像。在我第一次点击时，一切都正常

我的Aspx

<asp:UpdatePanel ID="UpdatePanel2" runat="server">
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="btnSubmit" />
    </Triggers>
    <ContentTemplate>
        <div class="form-group row">
            <div class="col-sm-6">
                <p style="margin: 0 0 5px 0;"><b>Class</b></p>
                <asp:DropDownList ID="drpClass" CssClass="form-control" OnSelectedIndexChanged="drpClass_SelectedIndexChanged" AutoPostBack="true" runat="server"></asp:DropDownList>
            </div>
            <div class="col-sm-6">
                <p style="margin: 0 0 5px 0;"><b>Division</b></p>
                <asp:DropDownList ID="drpDiv" CssClass="form-control"
                    runat="server">
                </asp:DropDownList>
            </div>
        </div>
        <div class="form-group row">
            <div class="col-sm-6">
                <p style="margin: 0 0 5px 0;"><b>Date</b></p>
                <asp:TextBox runat="server" ID="txtDateGiven" CssClass="form-control"
                    placeholder="Select a Date"></asp:TextBox>
                <asp:CalendarExtender ID="CalendarExtender2" runat="server" Format="dd/MMM/yyyy" PopupButtonID="txtDateGiven"
                    TargetControlID="txtDateGiven">
                </asp:CalendarExtender>
            </div>

            <div class="col-sm-6">
                <p style="margin: 0 0 5px 0;"><b>Date of Submission</b></p>
                <asp:TextBox runat="server" ID="txtDateSubmit" CssClass="form-control"
                    placeholder="Select a Date"></asp:TextBox>
                <asp:CalendarExtender ID="CalendarExtender1" runat="server" Format="dd/MMM/yyyy" PopupButtonID="txtDateSubmit"
                    TargetControlID="txtDateSubmit">
                </asp:CalendarExtender>
            </div>
        </div>

        <div class="form-group row">
            <div class="col-sm-12">
                <p style="margin: 0 0 5px 0;"><b>Subject</b></p>
                <asp:DropDownList ID="drpSubject" CssClass="form-control" runat="server"></asp:DropDownList>
            </div>
        </div>
        <div class="form-group row">
            <div class="col-sm-12">
                <p style="margin: 0 0 5px 0;"><b>Type</b></p>
                <asp:DropDownList ID="drpAssignmentType" CssClass="form-control" runat="server"></asp:DropDownList>
            </div>
        </div>
        <div class="form-group row">
            <div class="col-sm-12">
                <p style="margin: 0 0 5px 0;"><b>Title</b></p>
                <asp:TextBox ID="txtAssignmentTitle" CssClass="form-control" placeholder="Enter Title"
                    runat="server"></asp:TextBox>
            </div>
        </div>
        <div class="form-group row">
            <div class="col-sm-12">
                <p style="margin: 0 0 5px 0;"><b>Description</b></p>
                <asp:TextBox ID="txtAssignmentDes" CssClass="form-control" TextMode="MultiLine" Height="250"
                    placeholder="Enter Description"
                    runat="server"></asp:TextBox>
            </div>
        </div>
    </ContentTemplate>
</asp:UpdatePanel>
<asp:UpdatePanel ID="UpdatePanel3" runat="server">
    <Triggers>
        <asp:PostBackTrigger ControlID="btnUpload" />
    </Triggers>
    <ContentTemplate>
        <div class="form-group row">
            <div class="col-sm-6">
                <p style="margin: 0 0 5px 0;"><b>Upload File</b></p>
                <asp:FileUpload ID="imgPhoto" runat="server" />
                <br />
                <asp:Button ID="btnUpload" Text="Upload" runat="server" OnClick="btnUpload_Click"  />
                <% if (ViewState["Image"] != null)
                    {%>
                <a target="_blank" href="<%=ViewState["ImageName"]%>">View Attachment</a>
                <%}
                    else
                    { %>
                <asp:Label ID="Label1" runat="server" ForeColor="Red" Text="No File Uploaded"></asp:Label>
                <%} %>
            </div>
        </div>
    </ContentTemplate>
</asp:UpdatePanel>
<asp:UpdateProgress ID="updProgress" AssociatedUpdatePanelID="UpdatePanel1"
    runat="server">
    <ProgressTemplate>
        <div class="modal">
            <div class="center">
                <span style="padding-left: 10px"><b>Please Wait..</b></span>
                <img alt="" src="../images/Preloader_3.gif" width="50" height="50" />
            </div>
        </div>
    </ProgressTemplate>
</asp:UpdateProgress>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="btnSubmit" EventName="Click" />
    </Triggers>
    <ContentTemplate>
        <div class="form-group row">
            <div class="col-sm-6">
                <div class="col-sm-6">
                    <asp:Button ID="btnSubmit" OnClick="btnSubmit_Click"
                        CssClass="btn btn-primary" OnClientClick="javascript:return btnSubmit();"
                        runat="server" Text="Submit" AutoPostBack="true" />
                    <a href="assignment.aspx?sid=<%=Request.QueryString["sid"] %>" class="btn btn-default">Cancel</a>
                </div>
            </div>
        </div>
    </ContentTemplate>
</asp:UpdatePanel>
</div>

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可能这是一个重复的问题，但我需要解决我的问题

将其从代码中删除

updProgress.Visible = true;
updProgress.Visible = false;

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当我从代码中删除可见性控件时，我得到了这个结果。如果它在，那么隐藏和显示它是没有意义的synchronization@Yogesh是，因此建议从abve答案中的代码隐藏中删除此代码。那是我的错误

updProgress.Visible = true;
updProgress.Visible = false;