Split checkbox demo into client-only and remote

Controllers/Validations.cs

@@ -11,9 +11,9 @@ public IActionResult CheckRemote(string id)
     }
 
     [HttpPost]
-    public IActionResult CheckboxRemote(bool isChecked)
+    public IActionResult CheckboxRemote(bool isChecked, bool isCheckedToo)
     {
-        return Ok(isChecked);
+        return Ok(isChecked == isCheckedToo);
     }
 
     [HttpGet]

Pages/Demos/Checkboxes.cshtml

@@ -15,6 +15,7 @@
     <legend>Required ASP.NET Checkboxes (with hidden input) and Radio buttons</legend>
 
     <form method="post">
+
         <div class="form-field">
             <p>
                 ASP.NET renders a checkbox and a hidden input for each boolean property.
@@ -32,6 +33,20 @@
             }
         </div>
 
+        <div class="form-field">
+            <p>
+                One can also use the <code>[Remote]</code> validation attribute with checkboxes.
+                This checkbox's remote validator returns valid only when it matches the one above.
+                <strong>Note:</strong> Changes to
+                <a href="https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc.remoteattributebase.additionalfields">additional fields</a>
+                do <em>not</em> automatically revalidate.
+            </p>
+            <label>Is checked, too
+                <input asp-for="Input.IsCheckedToo"/>
+            </label>
+            <span asp-validation-for="Input.IsCheckedToo"></span>
+        </div>
+
         <div class="form-field">
             <p>
                 However, if you manually render a checkbox, the checkbox is only submitted
@@ -101,6 +116,7 @@
         </div>
 
         <input type="submit" value="Submit"/>
+
     </form>
 </fieldset>
 

Pages/Demos/Checkboxes.cshtml.cs

@@ -41,8 +41,13 @@ public IActionResult OnPost()
 
     public class InputModel
     {
-        [Remote("CheckboxRemote", "Validations", HttpMethod = "Post")]
         public bool IsChecked { get; set; }
+
+        [Remote("CheckboxRemote", "Validations", HttpMethod = "Post",
+            ErrorMessage = "Must match other checkbox.",
+            AdditionalFields = $"{nameof(IsChecked)}"
+        )]
+        public bool IsCheckedToo { get; set; }
     }
 
     [BindProperty]
@@ -54,4 +59,4 @@ public class Selectable
 
         public bool IsSelected { get; set; }
     }
-}
+}