Currently, in September 2023, LiveView does not offer an easy way to check if the @streams does not contain elements. The information is essential if we want a different UI for our empty state. After some research, I saw a post from “codeanpeace” on the Elixir Forum proposing using some Tailwind helpers. I decided to give it a try, and it works pretty great.

The final solution will be like this:

Now, let’s dive into the code. Our list is very straightforward. We added a boards key with the list of “boards” to our stream and will use this later in the html.

defmodule ReflectiveLoopWeb.BoardLive.Index do
  use ReflectiveLoopWeb, :live_view
  alias ReflectiveLoop.Retro

  @impl true
  def mount(_params, _session, socket) do
    {:ok, stream(socket, :boards, Retro.list_boards())}
  end
  # ...
end

I use a custom component to display a list that applies my desired style. I’ve omitted the non-essential parts. The critical factor is the render_slot(@new_item_action). Notice that it’s inside the div that will have the items from the @streams. The stacked_list component doesn’t know about the style of the slot, so we have the freedom to have lists with or without a custom empty state.

  def stacked_list(assigns) do
    ~H"""
    <div id={@id}>
      <div phx-update="stream" id="board-list">
        <%= render_slot(@new_item_action) %>

        <div :for={{dom_id, line} <- @lines} id={dom_id} role="list">
          <div>
            <p>
              <a href="#">
                <%= render_slot(@title, line) %>
              </a>
            </p>
          </div>
        </div>
      </div>
    </div>
    """
  end

Now, for the html part, we will use some pseudo-classes to change the style of the new item button, considering if the list is empty or not. I opted to use a single link with some extra css applied when it is the only element in the list.

Let’s check how the component works. Again, I’ve omitted the non-essential parts. As you can see, it’s straightforward. What makes the “magic” is the only pseudo-class that I’ve applied in the link.

<.stacked_list
  id="boards"
  lines={@streams.boards}
>
  <:title :let={board} label="name">
    <%= board.name %>
  </:title>

  <:new_item_action>
    <.link
      id="new-action-button"
      patch={~p"/boards/new"}
      class="only:block only:relative only:w-full only:rounded-lg only:bg-white only:border-2 only:border-dashed only:border-gray-300 only:p-12 only:text-center"
    >
      <.icon name="hero-inbox-stack-solid" class="text-gray-900" />

      <span class="pl-1 text-sm font-semibold text-gray-900">
        Create a new board
      </span>
    </.link>
  </:new_item_action>
</.stacked_list>

The structure needs to have a specific format. We have a div with two children, and we use Tailwind to display extra css when the link is the only child.

<div phx-update="stream">
  <a></a>
  <div></div>
</div>

But there is an a and a div, so we always have two children, no? Actually, no. The tag is not rendered when no items are in the @streams. In the empty state, the HTML will be a single child tag.

<div>
  <a></a>

</div>

I have never considered using CSS to handle states, but this works well with streams. If you don’t use Tailwind, style your div with :only-child, and you have the same result.