Phoenix.View (phoenix_view v1.0.0) View Source

Defines the view layer of a Phoenix application.

The view layer contains conveniences for rendering templates, including support for layouts and encoders per format.

Examples

Phoenix defines the view template at lib/your_app_web.ex:

defmodule YourAppWeb do
  # ...

  def view do
    quote do
      use Phoenix.View, root: "lib/your_app_web/templates", namespace: "web"

      # Import convenience functions from controllers
      import Phoenix.Controller,
        only: [get_flash: 1, get_flash: 2, view_module: 1, view_template: 1]

      # Use all HTML functionality (forms, tags, etc)
      use Phoenix.HTML

      import YourAppWeb.ErrorHelpers
      import YourAppWeb.Gettext

      # Alias the Helpers module as Routes
      alias  YourAppWeb.Router.Helpers, as: Routes
    end
  end

  # ...
end

You can use the definition above to define any view in your application:

defmodule YourApp.UserView do
  use YourAppWeb, :view
end

Because we have defined the template root to be "lib/your_app_web/templates", Phoenix.View will automatically load all templates at "your_app_web/templates/user" and include them in the YourApp.UserView. For example, imagine we have the template:

# your_app_web/templates/user/index.html.heex
Hello <%= @name %>

The .heex extension maps to a template engine which tells Phoenix how to compile the code in the file into Elixir source code. After it is compiled, the template can be rendered as:

Phoenix.View.render_to_string(YourApp.UserView, "index.html", name: "John Doe")
#=> "Hello John Doe"

Differences to `Phoenix.LiveView`

Traditional web applications, that rely on a request/response life cycle, have been typically organized under the Model-View-Controller pattern. In this case, the Controller is responsible for organizing interacting with the model and passing all relevant information to the View for rendering. Phoenix.Controller and Phoenix.View play those roles respectively.

Phoenix.LiveView introduces a declarative model where the controller and the view are kept side by side. This empowers Phoenix.LiveView to provide realtime and interactive features under a stateful connection.

In other words, you may consider that Phoenix.LiveView abridges both Phoenix.Controller and Phoenix.View responsibilities. Developers do not generally use Phoenix.View from their live views, but LiveView does use Phoenix.View and its features under the scenes.

Rendering and formats

The main responsibility of a view is to render a template.

A template has a name, which also contains a format. For example, in the previous section we have rendered the "index.html" template:

Phoenix.View.render_to_string(YourApp.UserView, "index.html", name: "John Doe")
#=> "Hello John Doe"

While we got a string at the end, that's not actually what our templates render. Let's take a deeper look:

Phoenix.View.render(YourApp.UserView, "index.html", name: "John Doe")
#=> ...

This inner representation allows us to separate how templates render and how they are encoded. For example, if you want to render JSON data, we could do so by adding a "show.json" entry to render/2 in our view:

defmodule YourApp.UserView do
  use YourApp.View

  def render("show.json", %{user: user}) do
    %{name: user.name, address: user.address}
  end
end

Notice that in order to render JSON data, we don't need to explicitly return a JSON string! Instead, we just return data that is encodable to JSON. Now, when we call:

Phoenix.View.render_to_string(YourApp.UserView, "user.json", user: %User{...})

Because the template has the .json extension, Phoenix knows how to encode the map returned for the "user.json" template into an actual JSON payload to be sent over the wire.

Phoenix ships with some template engines and format encoders, which can be further configured in the Phoenix application. You can read more about format encoders in Phoenix.Template documentation.

Link to this section Summary

Functions

__using__(opts)

When used, defines the current module as a main view module.

render(module, template, assigns)

Renders a template.

render_existing(module, template, assigns \\ []) deprecated

Renders a template only if it exists.

render_layout(module, template, assigns, list)

Renders the given layout passing the given do/end block as @inner_content.

render_many(collection, view, template, assigns \\ %{})

Renders a collection.

render_one(resource, view, template, assigns \\ %{})

Renders a single item if not nil.

render_to_iodata(module, template, assign)

Renders the template and returns iodata.

render_to_string(module, template, assign)

Renders the template and returns a string.

Link to this section Functions

using(opts)

(macro)

When used, defines the current module as a main view module.

Options

:root - the template root to find templates
:path - the optional path to search for templates within the :root. Defaults to the underscored view module name. A blank string may be provided to use the :root path directly as the template lookup path
:namespace - the namespace to consider when calculating view paths
:pattern - the wildcard pattern to apply to the root when finding templates. Default "*"

The :root option is required while the :namespace defaults to the first nesting in the module name. For instance, both MyApp.UserView and MyApp.Admin.UserView have namespace MyApp.

The :namespace and :path options are used to calculate template lookup paths. For example, if you are in MyApp.UserView and the namespace is MyApp, templates are expected at Path.join(root, "user"). On the other hand, if the view is MyApp.Admin.UserView, the path will be Path.join(root, "admin/user") and so on. For explicit root path locations, the :path option can be provided instead. The :root and :path are joined to form the final lookup path. A blank string may be provided to use the :root path directly as the template lookup path.

Setting the namespace to MyApp.Admin in the second example will force the template to also be looked up at Path.join(root, "user").

render(module, template, assigns)

Renders a template.

It expects the view module, the template as a string, and a set of assigns.

Notice that this function returns the inner representation of a template. If you want the encoded template as a result, use render_to_iodata/3 instead.

Examples

Phoenix.View.render(YourApp.UserView, "index.html", name: "John Doe")
#=> {:safe, "Hello John Doe"}

Assigns

Assigns are meant to be user data that will be available in templates. However, there are keys under assigns that are specially handled by Phoenix, they are:

:layout - tells Phoenix to wrap the rendered result in the given layout. See next section

Layouts

Templates can be rendered within other templates using the :layout option. :layout accepts a tuple of the form {LayoutModule, "template.extension"}.

To template that goes inside the layout will be placed in the @inner_content assign:

<%= @inner_content %>

render_existing(module, template, assigns \\ [])

This function is deprecated. Use function_exported?/3 instead.

Renders a template only if it exists.

Note: Using this functionality has been discouraged in recent Phoenix versions, see the "Alternatives" section below.

This function works the same as render/3, but returns nil instead of raising. This is often used with Phoenix.Controller.view_module/1 and Phoenix.Controller.view_template/1, which must be imported into your views. See the "Examples" section below.

Alternatives

This function is discouraged. If you need to render something conditionally, the simplest way is to check for an optional function in your views.

Consider the case where the application has a sidebar in its layout and it wants certain views to render additional buttons in the sidebar. Inside your sidebar, you could do:

<div class="sidebar">
  <%= if function_exported?(view_module(@conn), :sidebar_additions, 1) do
    <%= view_module(@conn).sidebar_additions(assigns) %>
  <% end %>
</div>

If you are using Phoenix.LiveView, you could do similar by accessing the view under @socket:

<div class="sidebar">
  <%= if function_exported?(@socket.view, :sidebar_additions, 1) do
    <%= @socket.view.sidebar_additions(assigns) %>
  <% end %>
</div>

Then, in your view or live view, you do:

def sidebar_additions(assigns) do
  ~H\"""
  ...my additional buttons...
  \"""

Using render_existing

Consider the case where the application wants to allow entries to be added to a sidebar. This feature could be achieved with:

<%= render_existing view_module(@conn), "sidebar_additions.html", assigns %>

Then the module under view_module(@conn) can decide to provide scripts with either a precompiled template, or by implementing the function directly, ie:

def render("sidebar_additions.html", _assigns) do
  ~H"""
  ...my additional buttons...
  """
end

To use a precompiled template, create a scripts.html.eex file in the templates directory for the corresponding view you want it to render for. For example, for the UserView, create the scripts.html.eex file at your_app_web/templates/user/.

render_layout(module, template, assigns, list)

Renders the given layout passing the given do/end block as @inner_content.

This can be useful to implement nested layouts. For example, imagine you have an application layout like this:

# layout/app.html.heex
<html>
<head>
  <title>Title</title>
</head>
<body>
  <div class="menu">...</div>
  <%= @inner_content %>
</body>

This layout is used by many parts of your application. However, there is a subsection of your application that wants to also add a sidebar. Let's call it "blog.html". You can build on top of the existing layout in two steps. First, define the blog layout:

# layout/blog.html.heex
<%= render_layout LayoutView, "app.html", assigns do %>
  <div class="sidebar">...</div>
  <%= @inner_content %>
<% end %>

And now you can simply use it from your controller:

plug :put_layout, "blog.html"

render_many(collection, view, template, assigns \\ %{})

Renders a collection.

A collection is any enumerable of structs. This function returns the rendered collection in a list:

render_many users, UserView, "show.html"

is roughly equivalent to:

Enum.map(users, fn user ->
  render(UserView, "show.html", user: user)
end)

The underlying user is passed to the view and template as :user, which is inferred from the view name. The name of the key in assigns can be customized with the :as option:

render_many users, UserView, "show.html", as: :data

is roughly equivalent to:

Enum.map(users, fn user ->
  render(UserView, "show.html", data: user)
end)

render_one(resource, view, template, assigns \\ %{})

Renders a single item if not nil.

The following:

render_one user, UserView, "show.html"

is roughly equivalent to:

if user != nil do
  render(UserView, "show.html", user: user)
end

The underlying user is passed to the view and template as :user, which is inflected from the view name. The name of the key in assigns can be customized with the :as option:

render_one user, UserView, "show.html", as: :data

is roughly equivalent to:

if user != nil do
  render(UserView, "show.html", data: user)
end

render_to_iodata(module, template, assign)

Renders the template and returns iodata.

render_to_string(module, template, assign)

Renders the template and returns a string.

Phoenix.View (phoenix_view v1.0.0) View Source

Examples

Differences to Phoenix.LiveView

Rendering and formats

Link to this section Summary

Functions

Link to this section Functions

__using__(opts)

Options

render(module, template, assigns)

Examples

Assigns

Layouts

render_existing(module, template, assigns \\ [])

Alternatives

Using render_existing

render_layout(module, template, assigns, list)

render_many(collection, view, template, assigns \\ %{})

render_one(resource, view, template, assigns \\ %{})

render_to_iodata(module, template, assign)

render_to_string(module, template, assign)

Differences to `Phoenix.LiveView`

using(opts)