上传图片，显示并允许上传下一张图片

Question

我在asp.net（VS2012）中写了这个事件。我希望用户上传图像和说明，上传后我想在页面的网格视图中显示图像名称和描述，并允许上传下一张图像。我不确定为什么事件被调用两次，第二次我在“if strfile.hasfile ...”中得到“Object reference not set to ....”错误。希望我能正确解释。

    Protected Sub btnUpload_Click(sender As Object, e As EventArgs) Handles btnUpload.Click
    Dim strfilename, strfilepath As String
    strfilename = Nothing
    strfilepath = lblInciID.Text.Trim
    Try
        ' Dim CurrentPath As String = Server.MapPath("C:\DSimages\")
        If strFile.HasFile Then
            Try
                strFile.SaveAs("C:\DSimages\" & _
                   strfilepath + strFile.FileName)
                'Save the name in the table
                strfilename = strFile.PostedFile.FileName
                strfilename = strfilepath + strfilename
                If strFile.HasFile Then strFile = Nothing
            Catch ex As Exception
                MsgBox("ERROR: " & ex.Message.ToString())
            End Try
        End If

        ImageDS.InsertParameters("ImagePath").DefaultValue = strfilename.Trim
        ImageDS.InsertParameters("ImageDescription").DefaultValue = txtPicDesc.Text.Trim()
        ImageDS.InsertParameters("InciID").DefaultValue = lblInciID.Text.Trim()
        ImageDS.InsertParameters("Category").DefaultValue = lblCategory.Text.Trim()
        ImageDS.Insert()
        'MsgBox("Picure was uploaded successfully! Upload another picture or click on 'Cancel'")
        txtPicDesc.Text = ""

    Catch ex As Exception
        MsgBox(ex.Message)
    End Try

    GridView_Image.Visible = True

End Sub   

aspx页面：

    <div class="clearclass padtop">
        <div class="div2">
            <h4 style="width:23.2em">Browse file</h4>
            <asp:FileUpload runat="server" ID="strFile" width="25em" Height="30px"/><br />
            <asp:Label runat="server" ID="imgtoupload"></asp:Label>
            <asp:RequiredFieldValidator ID="RequiredFieldValidatorFile" runat="server" ErrorMessage="File" ControlToValidate="strFile" 
                CssClass="fontred style_bold" Display="Static">File</asp:RequiredFieldValidator>
        </div>
        <div class="div2">
            <h4 style="width:24.6em">Add Description</h4>
            <asp:TextBox runat="server" ID="txtPicDesc" Width="30.4em" Height="5em" TextMode="MultiLine"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidatorDesc" runat="server" ControlToValidate="txtPicDesc" CssClass="fontred style_bold" 
                ErrorMessage="Description">Description</asp:RequiredFieldValidator>
        </div>
    </div>
<asp:GridView ID="GridView_Image" runat="server" DataSourceID="ImageDS" AutoGenerateColumns="False" HorizontalAlign="Center" Visible="false">
            <Columns>
                <asp:BoundField DataField="InciID" HeaderText="InciID" SortExpression="InciID" />
                <asp:BoundField DataField="Imagepath" HeaderText="Imagepath" SortExpression="Imagepath" />
                <asp:BoundField DataField="ImageDescription" HeaderText="ImageDescription" SortExpression="ImageDescription" />
            </Columns>
            <RowStyle BackColor="#EFF3FB" Height="2em" />
        </asp:GridView>