View Source Live layouts
From Phoenix v1.7, your application is made of two layouts:
the root layout - this is a layout used by both LiveView and regular views. This layout typically contains the
<html>
definition alongside the head and body tags. Any content defined in the root layout will remain the same, even as you live navigate across LiveViews. The root layout is typically declared on the router withput_root_layout
and defined as "root.html.heex" in your layouts folderthe app layout - this is the default application layout which is rendered on both regular HTTP requests and LiveViews. It defaults to "app.html.heex"
Overall, those layouts are found in components/layouts
and are
embedded within MyAppWeb.Layouts
.
All layouts must call <%= @inner_content %>
to inject the
content rendered by the layout.
Root layout
The "root" layout is rendered only on the initial request and
therefore it has access to the @conn
assign. The root layout
is typically defined in your router:
plug :put_root_layout, html: {MyAppWeb.LayoutView, :root}
The root layout can also be set via the :root_layout
option
in your router via Phoenix.LiveView.Router.live_session/2
.
Application layout
The "app.html.heex" layout is rendered with either @conn
or
@socket
. Both Controllers and LiveViews explicitly define
the default layouts they will use. See the def controller
and def live_view
definitions in your MyAppWeb
to learn how
it is included.
For LiveViews, the default layout can be overidden in two different ways for flexibility:
The
:layout
option inPhoenix.LiveView.Router.live_session/2
, when set, will override the:layout
option given viause Phoenix.LiveView
The
:layout
option returned on mount, via{:ok, socket, layout: ...}
will override any previously set layout option
The LiveView itself will be rendered inside the layout wrapped by
the :container
tag.
Updating document title
Because the root layout from the Plug pipeline is rendered outside of
LiveView, the contents cannot be dynamically changed. The one exception
is the <title>
of the HTML document. Phoenix LiveView special cases
the @page_title
assign to allow dynamically updating the title of the
page, which is useful when using live navigation, or annotating the browser
tab with a notification. For example, to update the user's notification
count in the browser's title bar, first set the page_title
assign on
mount:
def mount(_params, _session, socket) do
socket = assign(socket, page_title: "Latest Posts")
{:ok, socket}
end
Then access @page_title
in the root layout:
<title><%= @page_title %></title>
You can also use the Phoenix.Component.live_title/1
component to support
adding automatic prefix and suffix to the page title when rendered and
on subsequent updates:
<Phoenix.Component.live_title prefix="MyApp – ">
<%= assigns[:page_title] || "Welcome" %>
</Phoenix.Component.live_title>
Although the root layout is not updated by LiveView, by simply assigning
to page_title
, LiveView knows you want the title to be updated:
def handle_info({:new_messages, count}, socket) do
{:noreply, assign(socket, page_title: "Latest Posts (#{count} new)")}
end
Note: If you find yourself needing to dynamically patch other parts of the
base layout, such as injecting new scripts or styles into the <head>
during
live navigation, then a regular, non-live, page navigation should be used
instead. Assigning the @page_title
updates the document.title
directly,
and therefore cannot be used to update any other part of the base layout.