Added new kb article asyncupload-clear-uploaded-files-from-the-server-side (#619)

Co-authored-by: KB Bot <[email protected]>

Author: github-actions[bot]

knowledge-base/asyncupload-clear-uploaded-files-from-the-server-side.md

@@ -0,0 +1,82 @@
+---
+title: Clear Uploaded Files From The Server  
+description: This article demonstrates how to reset the RadAsyncUpload control to its initial state with no files selected using server-side code.
+type: how-to
+page_title: Clear Uploaded Files From The Server 
+slug: asyncupload-clear-uploaded-files-from-the-server-side
+tags: radasyncupload, asp.net ajax, server-side, clear, reset
+res_type: kb
+ticketid: 1668634
+---
+
+## Environment
+
+<table>
+<tbody>
+<tr>
+<td>Product</td>
+<td>RadAsyncUpload for ASP.NET AJAX</td>
+</tr>
+<tr>
+<td>Version</td>
+<td>All</td>
+</tr>
+</tbody>
+</table>
+
+## Description
+
+I have a [RadAsyncUpload](https://docs.telerik.com/devtools/aspnet-ajax/controls/asyncupload/overview) control on an ASP.NET Web form along with other controls. I need to clear out all the controls after some server-side code is called after a button click. For other controls, I can easily set their value to an empty string or their default state. I would like to reset the RadAsyncUpload control to its initial state, with no files selected.
+
+This KB article also answers the following questions:
+
+- How can I reset RadAsyncUpload after submitting the form?
+- Is it possible to clear the RadAsyncUpload control using server-side code?
+- How to remove all files from RadAsyncUpload from the server-side?
+
+## Solution
+
+To clear the RadAsyncUpload control and reset it to its initial state using server-side code, you can call a JavaScript function that removes the uploaded files from the client-side. This approach involves using a RadButton for postback and a RadAjaxManager to update the controls without a full page postback.
+
+First, define the RadAsyncUpload, RadButton, and RadAjaxManager in your ASPX page as follows:
+
+````ASP.NET
+<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">
+    <AjaxSettings>
+        <telerik:AjaxSetting AjaxControlID="RadButton1">
+            <UpdatedControls>
+                <telerik:AjaxUpdatedControl ControlID="RadButton1" />
+            </UpdatedControls>
+        </telerik:AjaxSetting>
+    </AjaxSettings>
+</telerik:RadAjaxManager>
+
+<telerik:RadAsyncUpload ID="RadAsyncUpload1" runat="server"></telerik:RadAsyncUpload>
+<telerik:RadButton runat="server" ID="RadButton1" Text="Postback" AutoPostBack="true" OnClick="RadButton1_Click" />
+````
+
+Next, add the following JavaScript function to your page. This function uses the client-side API of RadAsyncUpload to clear the files:
+
+````JavaScript
+function clearUploadedFiles() {
+    let upload = $find("<%= RadAsyncUpload1.ClientID %>");
+    upload.deleteAllFileInputs();
+}
+````
+
+Finally, call this JavaScript function from the server-side event handler of the button click event. Use the `ScriptManager.RegisterStartupScript` method to execute the JavaScript function from the server-side code:
+
+````C#
+protected void RadButton1_Click(object sender, EventArgs e)
+{
+    ScriptManager.RegisterStartupScript(this, GetType(), "key", "clearUploadedFiles();", true);
+}
+````
+
+By following these steps, you can successfully reset the RadAsyncUpload control to its initial state with no files selected after a server-side event.
+
+## See Also
+
+- [RadAsyncUpload Overview](https://docs.telerik.com/devtools/aspnet-ajax/controls/asyncupload/overview)
+- [RadAsyncUpload Client-Side Programming](https://docs.telerik.com/devtools/aspnet-ajax/controls/asyncupload/client-side-programming/overview)
+- [RadAjaxManager Overview](https://docs.telerik.com/devtools/aspnet-ajax/controls/ajaxmanager/overview)