Merge combobox-kb-autoselect-3032 into production (#3045)

* docs(kb): add kb for automatically select

* chore: modify solution section

---------

Co-authored-by: Tsvetomir Hristov <[email protected]>

Author: github-actions[bot]

knowledge-base/combobox-auto-select-on-blur.md

@@ -0,0 +1,185 @@
+---
+title: How to Automatically Select Preselected Item on Blur
+description: Learn how to configure the Telerik ComboBox for Blazor to automatically select the first matching item when the input loses focus.
+type: how-to
+page_title: How to Automatically Select Preselected Item on Blur
+slug: combobox-kb-autoselect-on-blur
+tags: telerik, blazor, combobox, blur, auto-select
+res_type: kb
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>ComboBox for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+
+The article asnwers to the following question:
+
+* How to configure the ComboBox to automatically select the first matching item when the input loses focus (e.g., when the user tabs away or clicks outside)?
+* How to auto-select a ComboBox item based on user input when focus is lost?
+* Can the ComboBox select a suggested item on blur without pressing Enter?
+* How to set the ComboBox value when the user leaves the input field?
+
+## Solution
+To automatically select the first matching item in the ComboBox when the input loses focus, use a combination of the ComboBox [`OnRead` event](slug:components/combobox/events#onread) and JavaScript interop. The provided example demonstrates how to:
+
+1. Use the `OnRead` event to filter data and store the first matching item.
+2. Attach a JavaScript event handler to detect when the user blurs the ComboBox input.
+3. Invoke a .NET method from JavaScript to set the ComboBox value to the first matching item when focus is lost.
+4. Update the ComboBox selection programmatically and refresh the UI.
+
+>caption Auto-select the first matching item on blur
+
+````RAZOR
+@using Telerik.DataSource.Extensions
+
+@implements IDisposable
+
+@inject IJSRuntime js
+
+<p>ComboBoxFirstItem: @ComboBoxFirstItem?.Text</p>
+
+<p>Selected value: @ComboBoxValue</p>
+
+<TelerikComboBox OnRead="@OnComboBoxRead"
+                 TItem="@ListItem"
+                 TValue="@int"
+                 Value="@ComboBoxValue"
+                 ValueChanged="@( (int newValue) => ComboBoxValueChanged(newValue) )"
+                 TextField="@nameof(ListItem.Text)"
+                 ValueField="@nameof(ListItem.Id)"
+                 Filterable="true"
+                 FilterOperator="@StringFilterOperator.Contains"
+                 Placeholder="Select an item..."
+                 ShowClearButton="true"
+                 Width="200px"
+                 Id="combo-1">
+    <ComboBoxSettings>
+        <ComboBoxPopupSettings Class="select-on-tab" />
+    </ComboBoxSettings>
+</TelerikComboBox>
+<br/>
+<br/>
+<TelerikTextBox Placeholder="Next form item" Width="200px"/>
+
+@* Move JavaScript to a separate JS file *@
+<script suppress-error="BL9992">
+        function attachComboKeyDown(selector) {
+            var comboInput = document.querySelector(selector);
+            if (comboInput) {
+                comboInput.addEventListener("keydown", onComboInputKeyDown);
+            }
+        }
+
+        function detachComboKeyDown(selector) {
+            var comboInput = document.querySelector(selector);
+            if (comboInput) {
+                comboInput.removeEventListener("keydown", onComboInputKeyDown);
+            }
+        }
+
+        function onComboInputKeyDown(e) {
+            if (e.key == "Tab") {
+                dotNet.invokeMethodAsync("OnComboBoxTab", e.target.value);
+            }
+        }
+
+        var dotNet;
+
+        function saveDotNetRef(dotNetRef) {
+            dotNet = dotNetRef;
+        }
+</script>
+
+@code {
+    private DotNetObjectReference<__Main>? DotNetRef { get; set; }
+
+    private List<ListItem> ComboBoxData { get; set; } = new();
+    private int ComboBoxValue { get; set; }
+    private ListItem? ComboBoxFirstItem { get; set; }
+
+    [JSInvokable("OnComboBoxTab")]
+    public void OnComboBoxTab(string newStringValue)
+    {
+        if (ComboBoxFirstItem is not null && ComboBoxFirstItem.Text.Contains(newStringValue))
+        {
+            ComboBoxValue = ComboBoxFirstItem.Id;
+            ComboBoxFirstItem = default;
+
+            StateHasChanged();
+        }
+    }
+
+    private void ComboBoxValueChanged(int newValue)
+    {
+        ComboBoxValue = newValue;
+        ComboBoxFirstItem = default;
+    }
+
+    private async Task OnComboBoxRead(ReadEventArgs args)
+    {
+        var result = await ComboBoxData.ToDataSourceResultAsync(args.Request);
+
+        args.Data = result.Data;
+        args.Total = result.Total;
+
+        if (args.Request.Filters.Count > 0)
+        {
+            ComboBoxFirstItem = args.Data.Cast<ListItem>().First();
+        }
+        else
+        {
+            ComboBoxFirstItem = default;
+        }
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (firstRender)
+        {
+            await Task.Delay(1); // ensure HTML is ready
+            await js.InvokeVoidAsync("saveDotNetRef", DotNetRef);
+            await js.InvokeVoidAsync("attachComboKeyDown", "#combo-1");
+        }
+
+        await base.OnAfterRenderAsync(firstRender);
+    }
+
+    protected override void OnInitialized()
+    {
+        DotNetRef = DotNetObjectReference.Create(this);
+
+        for (int i = 1; i <= 24; i++)
+        {
+            ComboBoxData.Add(new ListItem()
+                {
+                    Id = i,
+                    Text = $"Item {i}"
+                });
+        }
+    }
+
+    public void Dispose()
+    {
+        DotNetRef?.Dispose();
+        _ = js.InvokeVoidAsync("detachComboKeyDown", "#combo-1");
+    }
+
+    public class ListItem
+    {
+        public int Id { get; set; }
+        public string Text { get; set; } = string.Empty;
+    }
+}
+````
+## See Also
+
+- [ComboBox Events](slug:components/combobox/events)