Added new kb article multiselect-retrieve-selected-items-client-side (#631)

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

Author: github-actions[bot]

knowledge-base/multiselect-retrieve-selected-items-client-side.md

@@ -0,0 +1,82 @@
+---
+title: Retrieve Selected Items Client-Side
+description: Learn how to capture selected items from RadMultiSelect using its change event and store them in a hidden field on an ASP.NET AJAX page.
+type: how-to
+page_title: Retrieve Selected Items Client-Side
+slug: multiselect-retrieve-selected-items-client-side
+tags: radmultiselect, asp.net ajax, client-side, onchange, javascript, hidden field
+res_type: kb
+ticketid: 1670936
+---
+
+## Environment
+
+<table>
+<tbody>
+<tr>
+<td>Product</td>
+<td>RadMultiSelect for ASP.NET AJAX</td>
+</tr>
+<tr>
+<td>Version</td>
+<td>All</td>
+</tr>
+</tbody>
+</table>
+
+## Description
+Capturing selected items from a [RadMultiSelect](https://docs.telerik.com/devtools/aspnet-ajax/controls/multiselect/overview) and storing them in a hidden field on the client side is needed when handling selections without postbacks. This KB article also answers the following questions:
+
+- How can I update a hidden field based on RadMultiSelect selections?
+- Is it possible to handle RadMultiSelect change events on the client side?
+- How do I store RadMultiSelect selected items in a web form?
+
+## Solution
+To list and store the selected items of a RadMultiSelect in a hidden field on an .aspx page, follow these steps:
+
+**Add a Hidden Field to Your Page:** Insert a hidden field in your .aspx page to hold the selected values.
+
+````ASP.NET
+<asp:HiddenField ID="hiddenFieldSelectedItems" runat="server" />
+````
+
+**Configure RadMultiSelect:** Set up the RadMultiSelect with the necessary configurations and client events.
+
+````ASP.NET
+<telerik:RadMultiSelect ID="RadMultiSelect1" runat="server" DataTextField="text" DataValueField="value" Filter="Contains" AutoPostBack="false">
+        <Items>
+            <telerik:MultiSelectItem Text="Element1" Value="1"></telerik:MultiSelectItem>
+            <telerik:MultiSelectItem Text="Element2" Value="2"></telerik:MultiSelectItem>
+            <telerik:MultiSelectItem Text="Element3" Value="3"></telerik:MultiSelectItem>
+        </Items>
+        <ClientEvents OnSelect="onSelect" />
+    </telerik:RadMultiSelect>
+````
+
+**Implement JavaScript Function:** Create a JavaScript function to update the hidden field with the texts of the selected items, separated by commas.
+
+````JavaScript
+function onSelect(sender, args) {
+        let selectedTexts = [];
+        let selectedItems = sender.get_selectedDataItems();
+        let hiddenField = document.getElementById('<%= hiddenFieldSelectedItems.ClientID %>');
+
+        if (selectedTexts.length < 1) {
+            selectedTexts.push(args.get_dataItem().text)
+        }
+
+        for (let i = 0; i < selectedItems.length; i++) {
+            selectedTexts.push(selectedItems[i].text);
+        }
+
+        hiddenField.value = selectedTexts.join(", ");
+    }
+````
+
+### Explanation
+- **JavaScript Approach:** Utilizing JavaScript allows for real-time updates to the hidden field without the need for postbacks, enhancing the user experience.
+- **Handling Events:** The `OnChange` event of the RadMultiSelect ensures the hidden field is consistently synchronized with the user's selections.
+
+## See Also
+- [RadMultiSelect Overview](https://docs.telerik.com/devtools/aspnet-ajax/controls/multiselect/overview)
+- [Client-Side Programming](https://docs.telerik.com/devtools/aspnet-ajax/controls/multiselect/client-side-programming/overview)