Preview selected image & then upload to server in vb.net

Question

Please Don't mark it as repeated question. I know how to preview image before uploading to web server & I tried as following code. But then how do I upload same file on web server because after postback file upload losses selected files value. I just want to know how will it upload to server & also if multiple files selected?

<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 code

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

It will have one more button to upload a file.

Answer 1

You can try stopping the postback with

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

to avoid losing the recently loaded image

Or retain the image in the Session object:

'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