asp.net - 回发后 FileUpload 控件的保留路径

Question

我在 UpdatePanel 中有一个 FileUpload 控件和一个 DropDownlist 控件，当用户为 FileUpload 控件选择一个文件(尚未上传)时，同时用户从 DropDownList 控件中选择一个选项，这将导致回发!一旦页面回发，在 FileUpload 控件中选择的路径将消失。如何保留 FileUpload 控件中的路径？文件上传功能正在运行。我希望在回发期间可以保留 FileUpload 控件中的路径。

我已经尝试了下面的解决方案，但“FileUpload1.HasFile”将返回 false。

            If Session("FileUpload1") Is Nothing AndAlso Upload.HasFile Then
                Session("FileUpload1") = Upload
                lblPhotoUploadErr.Text = Upload.FileName
            ElseIf Session("FileUpload1") IsNot Nothing AndAlso (Not Upload.HasFile) Then
                Upload = DirectCast(Session("FileUpload1"), FileUpload)
                lblPhotoUploadErr.Text = Upload.FileName
            ElseIf Upload.HasFile Then
                Session("FileUpload1") = Upload
                lblPhotoUploadErr.Text = Upload.FileName
            End If

但是下面上传函数中的“Upload.HasFile”在执行时会为真。

Public Sub uploadPhoto()
    Dim FileOK As Boolean = False
    Dim FileSaved As Boolean = False
    Dim CandidateCode As String = Nothing
    Dim newFileName As String = Nothing

    Dim extension As String = Nothing
    Dim fileNameWithoutExt As String = Nothing

    If txtCandidateCode.Text.Trim <> "" Then
        CandidateCode = txtCandidateCode.Text.Trim
    End If

    If Upload.HasFile Then
        Dim FileExtension As String = Path.GetExtension(Upload.FileName).ToLower
        Dim allowedExtensions() As String = {".png", ".jpeg", ".jpg", ".gif"}

        Dim i As Integer = 0
        Do While (i < allowedExtensions.Length)
            If (FileExtension = allowedExtensions(i)) Then
                FileOK = True
            End If
            i = (i + 1)
        Loop
    End If

    If FileOK Then
        Try
            fileNameWithoutExt = Path.GetFileNameWithoutExtension(Upload.FileName)
            extension = Path.GetExtension(Upload.FileName)
            newFileName = fileNameWithoutExt + "_" + CandidateCode + extension

            Upload.PostedFile.SaveAs((path1 + newFileName))
            FileSaved = True
        Catch ex As Exception
            lblPhotoUploadErr.Text = ("File could not be uploaded." + ex.Message.ToString)
            FileSaved = False
        End Try
    Else
        lblPhotoUploadErr.Text = "Cannot accept files of this type."
    End If

    If FileSaved Then
        pnlUpload.Visible = False
        imgPhoto.ImageUrl = ("~/images/" + newFileName)
        hfPhotoUploadPath.Value = ("~/images/" + newFileName)

        hfFileExtension.Value = extension
        hfPhotoUploadFileName.Value = fileNameWithoutExt
    End If
End Sub

Answer 1

如果您将 FileUpload 从 UpdatePanel 中取出，它只会保留它的值。这样你仍然可以用 DropDownList 和它的 AutoPostBack 做所有事情，但是 ajax-postback 不会刷新 FileUpload 导致它变空。这样你就不再需要 postbacktriggers 了。

把 UpdatePanel仅在 DropDownList 附近并且回发的任何控件都必须更改 .如果这些控件不相邻，您可以使用多个 UpdatePanel，AutoPostBack 将刷新所有控件(默认行为，您甚至可以更改它)。