Question

请不要将其标记为重复问题。我知道如何在上传到网络服务器之前预览图像＆amp;我试过以下代码。但是，我如何在Web服务器上传相同的文件，因为在回发文件上传丢失后选择文件值。我只是想知道它将如何上传到服务器＆amp;如果选择了多个文件？

<asp:FileUpload ID="FileUpload1" runat="server" /><br /><br />


    <asp:Image ID="preview1" runat="server" CssClass="preview" />

<asp:Button ID="delete1" runat="server" Text="Delete1" /><br />

<script type="text/javascript">
        function uploadPreview(fileUpload) {
            if (fileUpload.value != '') {
                document.getElementById("<%=Upload.ClientID %>").click();
        }
    }
    </script>

VB代码

Private Sub Online_Medicines_order_online_Default2_Load(sender As Object, e As EventArgs) Handles Me.Load
        FileUpload1.Attributes("onchange") = "uploadPreview(this)"
    End Sub
    Protected Sub uploadPreview(sender As Object, e As EventArgs)
        Dim fs As System.IO.Stream = FileUpload1.PostedFile.InputStream
        Dim br As New System.IO.BinaryReader(fs)
        Dim bytes As Byte() = br.ReadBytes(CType(fs.Length, Integer))
        Dim base64String As String = Convert.ToBase64String(bytes, 0, bytes.Length)
        If preview1.ImageUrl = "" Then
            preview1.ImageUrl = "data:image/png;base64," & base64String
            preview1.Visible = True
        End If
    End Sub

它还有一个按钮来上传文件。

Answer 1

您可以尝试使用

停止回发

<asp:FileUpload ID="FileUpload1" runat="server" OnClientClick="return false;"/>

以避免丢失最近加载的图像

或者将图像保留在Session对象中：

'If first time page is submitted and we have file in FileUpload control but not in session
'Store the values to SEssion Object
If (Session("FileUpload1") Is Nothing AndAlsdo FileUpload1.HasFile) Then  
    Session("FileUpload1") = FileUpload1
    Label1.Text = FileUpload1.FileName    
'Next time submit and Session has values but FileUpload is Blank
ElseIf (Session("FileUpload1") IsNot Nothing AndAlso (Not FileUpload1.HasFile)) Then    
    FileUpload1 = (FileUpload) Session("FileUpload1")
    Label1.Text = FileUpload1.FileName
' Session has File but user want to change the file
ElseIf (FileUpload1.HasFile) Then    
    Session("FileUpload1") = FileUpload1
    Label1.Text = FileUpload1.FileName
End IF

预览所选图像＆amp;然后上传到vb.net中的服务器

1 个答案: