Flash Messages

Flash messages are basically read-once messages attached to a controller response. They are attached to a user session and kept in memory until read.

Flash messages can persist through multiple redirects as long as nothing reads them in the process.

Enabling Flash Messages

To enable flash messages, you will need to register the Flash Message Middleware. The easiest way to do this is with the UseFlashMessages() extension method.

The Flash Message Middleware requires a Session Store, and will register an InMemorySessionStore if no other session store is found.

hostBuilder.UseFlashMessages();

Displaying Flash Messages

Any flash messages for the current session are available from the flash_messages variable in templates. Each message is an instance of FlashMessage and has a message and type fields.

You can use these to display flash messages in your templates.

{% if flash_messages %}
    <div class="container">
        {% for message in flash_messages %}
            <div class="alert alert-{{ message.type }}">{{ message.message }}</div>
        {% endfor %}
    </div>
{% endif %}

Sending Flash Messages

To create a new flash message and attach it to the session, you will need to get an instance of FlashService from DI and then call the AddFlashMessage method.

[Controller]
[Route("/")]
public class IndexController(FlashService flashService) : ControllerBase 
{
    [HttpGet]
    [Route("")]
    public ViewResult GetIndex() 
    {
        flashService.AddFlashMessage("Hello World!", FlashMessageType.Info);
        return View("index");
    }
}

Message Types

There are 5 predefined message types in the FlashService.FlashMessageType enum that translate into a string like this:

• Primary => primary
• Info => info
• Warning => warning
• Success => success
• Error => error

The FlashService#AddFlashMessage method has an overload that accepts a string for the type. You can pass in any custom value.

flashService.AddFlashMessage("Hey there!", "greeting");