added flashes with a couple of examples

Controllers/AccountController.cs

@@ -65,6 +65,7 @@ public async Task<IActionResult> Login(LoginViewModel model, string returnUrl =
                 if (result.Succeeded)
                 {
                     _logger.LogInformation("User logged in.");
+                    this.FlashSuccess("Logged in");
                     return RedirectToLocal(returnUrl);
                 }
                 if (result.RequiresTwoFactor)
@@ -247,6 +248,7 @@ public async Task<IActionResult> Logout()
         {
             await _signInManager.SignOutAsync();
             _logger.LogInformation("User logged out.");
+            this.FlashSuccess("Logged out");
             return RedirectToAction(nameof(HomeController.Index), "Home");
         }
 

Extensions/ControllerExtensions.cs

@@ -0,0 +1,38 @@
+namespace Microsoft.AspNetCore.Mvc
+{
+   public static class FlashMessages
+    {
+        public static string Info = "InfoMessage";
+        public static string Success = "SuccessMessage";
+        public static string Error = "ErrorMessage";
+        public static string Warning = "WarningMessage";
+    }
+
+    //TODO: allow mulitple flashes of same type???
+    public static class ControllerExtensions
+    {
+        static void FlashMessage(this Controller controller, string type, string message)
+        {
+            controller.TempData[type] = message;
+        }
+        public static void FlashInfo(this Controller controller, string message)
+        {
+            FlashMessage(controller, FlashMessages.Info, message);
+        }
+
+        public static void FlashSuccess(this Controller controller, string message)
+        {
+            FlashMessage(controller, FlashMessages.Success, message);
+        }
+
+        public static void FlashError(this Controller controller, string message)
+        {
+            FlashMessage(controller, FlashMessages.Error, message);
+        }
+
+        public static void FlashWarning(this Controller controller, string message)
+        {
+            FlashMessage(controller, FlashMessages.Warning, message);
+        }
+    }
+ }

Views/Shared/_FlashMessages.cshtml

@@ -0,0 +1,21 @@
+@using Microsoft.AspNetCore.Mvc.RazorPages
+
+@if (TempData.ContainsKey(FlashMessages.Error))
+{
+    <div class="alert alert-danger">@TempData[FlashMessages.Error]</div>
+}
+
+@if (TempData.ContainsKey(FlashMessages.Info))
+{
+    <div class="alert alert-info">@TempData[FlashMessages.Info]</div>
+}
+
+@if (TempData.ContainsKey(FlashMessages.Warning))
+{
+    <div class="alert alert-warning">@TempData[FlashMessages.Warning]</div>
+}
+
+@if (TempData.ContainsKey(FlashMessages.Success))
+{
+    <div class="alert alert-success" role="alert">@TempData[FlashMessages.Success]</div>
+}

Views/Shared/_Layout.cshtml

@@ -38,6 +38,9 @@
             </div>
         </div>
     </nav>
+
+    @await Html.PartialAsync("_FlashMessages")
+
     <div class="container body-content">
         @RenderBody()
         <hr />