I'm creating a .net program that uploads images to the FTP server. A blank listbox is populated dynamically on the client side from the value of the html input file widget. There is also a requiredfieldva lidator on the listbox to make sure there is an item in the listbox. When I click the button to submit, however, the listbox clears itself and a validation error shows. Below is the relevant code in C# plus the Javascript code. Thanks in advance.
.aspx code: -
<%@ Page Language="C#" ContentType="text/html" ResponseEncoding="utf-8" CodeFile="logopageAdmin.aspx.cs" Inherits="_Default" trace=true %>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>Untitled Document</title>
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</head>
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<body>
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<form id="attachme" method="post" encType="multipart/form-data" runat="server">
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<div id="fileSelection">
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<input type="file" id="fileDialog" name="fileDialog" />
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<input id="addFile" name="addFile" type="button" value="Add" onclick="addToList()" />
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</div>
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<div id="listEdit">
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<asp:ListBox ID="uploadList" runat="server" Rows="10" ValidationGroup="uploadSelection"></asp:ListBox><br/>
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<asp:RequiredFieldValidator ID="reqUpload" runat="server" ControlToValidate="uploadList" InitialValue="" EnableClientScript="true" Display="Dynamic" ErrorMessage="Please select files to upload<br/>" ValidationGroup="uploadSelection" />
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<input type="button" id="removeItem" name="removeItem" value="Remove Selected Files" onclick="removeFromList()" />
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<asp:Button ID="upload" runat="server" Text="Upload Files" OnClick="Upload_ServerClick" ValidationGroup="uploadSelection" />
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</div>
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<asp:TextBox ID="status" runat="server" TextMode="MultiLine" Rows="10" Columns="60" Wrap="true" Enabled="false" />
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...
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</form>
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</body>
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</html>
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C# code: -
protected void Page_Load(object sender, EventArgs e)
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{
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Page.RegisterClientScriptBlock("logopageAdminMain", "<script type=\"text/javascript\" src=\"logopageAdminScript.js\"></script>");
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...
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}
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-
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public void Upload_ServerClick(object sender, System.EventArgs e)
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{
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foreach (ListItem i in uploadList.Items)
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{
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try
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{
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//testing to see if listbox items are read
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Response.Write(i.Value + "<br/>");
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//upload code here
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}
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catch(Exception err)
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{
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//do code
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}
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}
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}
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javascript code: -
var listWidget;
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function addToList()
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{
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var fileWidget = document.getElementById("fileDialog");
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listWidget = document.getElementById("uploadList");
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if (fileWidget.value.substring(fileWidget.value.length - 4) == ".jpg" || fileWidget.value.substring(fileWidget.value.length - 4) == ".gif" || fileWidget.value.substring(fileWidget.value.length - 4) == ".png")
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{
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var newOption = document.createElement("Option");
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newOption.text = fileWidget.value;
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newOption.value = fileWidget.value;
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listWidget.options[listWidget.length] = newOption;
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}
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else
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{
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alert("Files must be either .jpg, gif, or .png");
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}
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}
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function removeFromList()
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{
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listWidget = document.getElementById("uploadList");
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for (var i = listWidget.length - 1; i>=0; i--)
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{
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if (listWidget.options[i].selected)
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{
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listWidget.remove(i);
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}
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}
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}
7  3132 
What i understand is that u have assigned the element in listbox from client side (i.e. from java script) addToList() doing this .. and when the postback occur server doesnot know the items of listbox and clear it out and after postback listbox contain no element in it ... for this u have to call the this addToList()
function when the postback occur ... bcoz client (browser) is stateless it can not maintain its state so u have to call java script function once again after the post back .....
Thanks, Shabazz, I'll give it a try! :D
Frinavale 9,735
Recognized Expert Moderator Expert
I'm creating a .net program that uploads images to the FTP server. A blank listbox is populated dynamically on the client side from the value of the html input file widget. There is also a requiredfieldva lidator on the listbox to make sure there is an item in the listbox. When I click the button to submit, however, the listbox clears itself and a validation error shows. Below is the relevant code in C# plus the Javascript code. Thanks in advance.
...
What is the validation error?
I think that ShahbazAshraf is right.
The server loads controls based on their ViewState.
When you add items to a listbox, you could be messing this up.
What is the validation error?
I think that ShahbazAshraf is right.
The server loads controls based on their ViewState.
When you add items to a listbox, you could be messing this up.
The validation error is line 16. It basically acts as if there were no items in the listbox at all.
Frinavale 9,735
Recognized Expert Moderator Expert
The validation error is line 16. It basically acts as if there were no items in the listbox at all.
Could you please copy/paste the exact error here.
Again, I'm sure it's because your ListBox is registered into your ViewState, changing the ListBox with JavaScript is going to mess this up and an error will occur....either that or the ListBox (when recreated on the server) will be empty upon postback every time (because it's loaded based on it's ViewState).
I'm creating a .net program that uploads images to the FTP server.
I don't think you can use a ListBox to upload files anyways.....
I'm pretty sure you can only use UploadControls (<input> is the html tag for it)
Have you seen this tutorial?
-Frinny
Below are the filepaths added to the listbox. 
After I click "Upload Files", the list box clears itself and I get the validation error. 
I did run across a control like the one you linked to. It just seemed easier to plug the item value from the listbox into FTPWebRequest. I'll look into that again, though.
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