回发后保持FileUpload控制的路径 [英] Remain path of FileUpload control after postback

问题描述

在一个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（还没有上传）的同时，用户从DropDownList控件中选择一个选项，这将导致一个回发！一旦页面回发，在FileUpload控件中选择的路径将消失。我怎么能保持在FileUpload控制的路径？文件上传功能正在工作。我希望在回发期间可以保持在FileUpload控件的路径。

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

 如果Session（FileUpload1）是Nothing并且上传.HasFile然后
 Session（FileUpload1）= Upload 
 lblPhotoUploadErr.Text = Upload.FileName 
 ElseIf Session（FileUpload1）IsNot Nothing AndAlso（Not Upload.HasFile）然后
 Upload = DirectCast（Session（FileUpload1），FileUpload）
 lblPhotoUploadErr.Text = Upload.FileName 
 ElseIf Upload.HasFile然后
 Session（FileUpload1）= Upload 
 lblPhotoUploadErr.Text = Upload.FileName 
 End If 
  

但是上传函数中的Upload.HasFile在执行时会为true。

  Public Sub uploadPhoto（）
 Dim F ileOK 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 
 
如果txtCandidateCode.Text.Trim<> Then 
 CandidateCode = txtCandidateCode.Text.Trim 
 End If 
 
如果Upload.HasFile然后
 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 
 $ b Upload.PostedFile.SaveAs（（path1 + newFileName））
 FileSaved = True 
赶上例外
 lblPhotoUploadErr.Text =（File could not be uploaded。+ ex.Message.ToString）
 FileSaved = False 
 End Try 
 Else 
 lblPhotoUploadErr.Text =无法接受文件这种类型。 
 End If 
 
如果FileSaved Then 
 pnlUpload.Visible = False 
 imgPhoto.ImageUrl =（〜/ images /+ newFileName）
 hfPhotoUploadPath。 Value =（〜/ images /+ newFileName）
 
 hfFileExtension.Value = extension 
 hfPhotoUploadFileName.Value = fileNameWithoutExt 
 End If 
 End Sub 
  

解决方案

如果您将FileUpload从UpdatePanel中取出。这样，你仍然可以使用DropDownList和AutoPostBack来做所有的事情，但是ajax-postback不会刷新FileUpload，导致它变空。这样你就不再需要postbacktriggers了。
$ b 将 UpdatePanel 放在 DropDownList 和任何控制回发必须改变。如果这些控件不相邻，则可以使用多个UpdatePanel，AutoPostBack将刷新所有这些控件（默认行为，甚至可以更改）。

I have a FileUpload control and a DropDownlist control in an UpdatePanel and when user select a file for the FileUpload control (no upload yet), in the meanwhile the user select an option from the DropDownList control which will cause a postback! Once the page postback, the path selected in the FileUpload control will gone. How can i remain the path in the FileUpload control? File uploading function was working. I hope can remain the path in the FileUpload control during postback.

I have tried the solution below but the "FileUpload1.HasFile" will return false to me.

            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

but the "Upload.HasFile" in the uploading function below will true when it was executed.

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

解决方案

The FileUpload will only keep it's value if you take it out of the UpdatePanel. That way you can still do everything with the DropDownList and its AutoPostBack but the ajax-postback won't refresh the FileUpload causing it to become empty. This way you don't need the postbacktriggers any more.

Put the UpdatePanel only around the DropDownList and any controls the postback has to change. If these controls are not next to each other you can use multiple UpdatePanels, the AutoPostBack will refresh all of them (default behavior, you can even change that).

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