Added new kb article datepicker-select-all-content-on-focus (#3408)

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

Author: kendo-bot

knowledge-base/datepicker-select-all-content-on-focus.md

@@ -0,0 +1,88 @@
+---
+title: How to Select All Content in DatePicker on Focus
+description: Learn how to ensure the entire content of the DatePicker input is selected on focus.
+type: how-to
+page_title: Automatically Select All Text in DatePicker Input on Focus
+meta_title: Automatically Select All Text in DatePicker Input on Focus
+slug: datepicker-kb-select-all-content-on-focus
+tags: datepicker, focus, input, selection
+res_type: kb
+ticketid: 1704388
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>DatePicker for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+
+I want the entire content of the [Telerik DatePicker](slug:components/datepicker/overview) input to be automatically selected when focused, allowing users to copy-paste dates directly.
+
+## Solution
+
+To ensure the entire input content is selected on focus and the popup calendar remains functional, follow these steps:
+
+1. Hide the default calendar button using CSS.
+2. Add a custom button for opening the popup calendar.
+3. Utilize the [`FocusAsync`](slug:components/datepicker/overview#datepicker-reference-and-methods) and a JavaScript function to select all text in the input.
+
+Here is the complete implementation:
+
+````Razor
+@inject IJSRuntime JS
+
+<style>
+    .k-datepicker button{
+        display: none;
+    }
+</style>
+
+<span @onclick="FocusAndSelect">
+    <TelerikDatePicker @ref="DatePickerRef"
+                       @bind-Value="DatePickerValue"
+                       Width="200px" />
+</span>
+<TelerikButton Icon="@SvgIcon.Calendar" OnClick="@OpenPicker" />
+
+<script>
+    window.selectDatePickerInput = function () {
+        // Finds the active element (the DatePicker input after FocusAsync)
+        const input = document.activeElement;
+        if (input && input.tagName === "INPUT") {
+            input.select();    // selects all text
+        }
+    }
+</script>
+
+@code {
+    private TelerikDatePicker<DateTime> DatePickerRef { get; set; }
+    private DateTime DatePickerValue { get; set; } = DateTime.Now;
+
+    private void OpenPicker()
+    {
+        DatePickerRef?.Open();
+    }
+
+    private async Task FocusAndSelect()
+    {
+        await DatePickerRef.FocusAsync();
+
+        // wait a moment so the input renders focus
+        await Task.Delay(20);
+
+        await JS.InvokeVoidAsync("selectDatePickerInput");
+    }
+}
+````
+
+## See Also
+
+* [DatePicker Documentation](slug:components/datepicker/overview)
+* [FocusAsync Method](slug:components/datepicker/overview#datepicker-reference-and-methods)