kb(Switch): Add KB for indeterminate Switch

Author: dimodi

knowledge-base/switch-indeterminate-state.md

@@ -0,0 +1,75 @@
+---
+title: Add Indeterminate Switch State
+description: Learn how to customize the Telerik Switch for Blazor and add an indeterminate state when the component Value is null.
+type: how-to
+page_title: How to Add Indeterminate State to the Telerik Switch for Blazor
+slug: switch-kb-indeterminate-state
+tags: blazor, switch, css, styling
+ticketid: 1677869, 1587745
+res_type: kb
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>Switch for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+
+This KB answers the following questions:
+
+* How to implement an indeterminate state feature for the Switch component with CSS?
+* How to use a Switch component with an undetermined state for nullable boolean values?
+* How to enable inteterminate Switch state when the value is null?
+
+## Solution
+
+1. Use a specific `Class` parameter value to toggle the indeterminate UI state of the Switch.
+1. [Apply custom CSS styles to override](slug:themes-override) the default Switch appearance.
+
+> Indeterminate Switches are uncommon and users may not identify or distinguish them easily. Also evaluate other options, such as [indeterminate checkboxes](slug:checkbox-indeterminate-state) or a [RadioGroup](slug:radiogroup-overview) with three visible options.
+
+>caption Switch with indeterminate state for null values
+
+````RAZOR
+<p>Switch <code>Value</code>: <code>@( SwitchValue?.ToString().ToLowerInvariant() ?? "null" )</code></p>
+
+<TelerikSwitch @bind-Value="@SwitchValue"
+               Class="@( SwitchValue.HasValue ? string.Empty : IndeterminateClass )" />
+
+<TelerikButton OnClick="@( () => SwitchValue = default )">Reset Switch</TelerikButton>
+
+<style>
+    /* Set a custom Switch background in indeterminate state. */
+    span.switch-indeterminate .k-switch-track {
+        background-color: var(--kendo-color-warning);
+    }
+
+    /* Hide Switch labels */
+    span.switch-indeterminate .k-switch-label-on,
+    span.switch-indeterminate .k-switch-label-off {
+        display: none;
+    }
+
+        /* Center the Switch thumb */
+        span.switch-indeterminate .k-switch-thumb {
+            transform: translate(0, -50%);
+        }
+</style>
+
+@code {
+    private bool? SwitchValue { get; set; }
+
+    private const string IndeterminateClass = "switch-indeterminate";
+}
+````
+
+## See Also
+
+* [CheckBox Indeterminate State](slug:checkbox-indeterminate-state)