cro

cro

Programming Phoenix LiveView: P27, live_path confusion

I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into the live_patch function to patch the view and add the button. Many examples involving live_patch I found on the web suggested something like

<%= live_patch to: Routes.live_path(@socket, __MODULE__), replace: true do %>
   <button>Try again!</button>
<%end>

but Elixir complains with

warning: Routes.live_path/2 is undefined (module Routes is not available or is yet to be defined)
  lib/pento_web/live/wrong_live.ex:50: PentoWeb.WrongLive.render/1

mix phx.routes says the helper is defined:

$ mix phx.routes
          page_path  GET  /                                      Phoenix.LiveView.Plug :index
          live_path  GET  /guess                                 Phoenix.LiveView.Plug PentoWeb.WrongLive
live_dashboard_path  GET  /dashboard                             Phoenix.LiveView.Plug :home
live_dashboard_path  GET  /dashboard/:page                       Phoenix.LiveView.Plug :page
live_dashboard_path  GET  /dashboard/:node/:page                 Phoenix.LiveView.Plug :page
          websocket  WS   /live/websocket                        Phoenix.LiveView.Socket
           longpoll  GET  /live/longpoll                         Phoenix.LiveView.Socket
           longpoll  POST  /live/longpoll                         Phoenix.LiveView.Socket
          websocket  WS   /socket/websocket                      PentoWeb.UserSocket

So I must be missing a use or alias somewhere? Help?

Marked As Solved

SophieDeBenedetto

SophieDeBenedetto

Author of Programming Phoenix LiveView

Hello and thank you all for your patience! A lot has changed in LiveView lately and Bruce and I are hard at work on a new version of the book with the latest version and all new code samples. Keep an eye out for that in the next few weeks.

In the meantime, yes the live path helpers have been replaced with the link/1 function component Phoenix.Component — Phoenix LiveView v0.19.5.

I believe the latest version of the book that is currently out does reflect this change though. Please do make sure you’re working off of the latest version. If you’ve purchased the e-book, you’ll be emailed when a new Beta release is made available for download and you’ll have access to download it for free.

Also Liked

SophieDeBenedetto

SophieDeBenedetto

Author of Programming Phoenix LiveView

Re-posting here for visibility bc I accidentally replied privately:

Mystery solved!

At the top of your PentoWeb.WrongLive module, you should pull in the LiveView behavior like this:

defmodule PentoWeb.WrongLive do
  use PentoWeb, :live_view

I think there was someplace in the book where we gave you an outdated instruction to do so like this instead:

defmodule PentoWeb.WrongLive do
  use Phoenix.LiveView

That has since been corrected but I’m not sure if the fix is out in the Beta release from last week or if it will be included in the next one. In either case, that is the change you need to make and I’m sorry for any confusion this caused!

Let me know if this un-sticks you or if you encounter any other errors :slight_smile:
And @cro confirmed this fixed the issue!

SophieDeBenedetto

SophieDeBenedetto

Author of Programming Phoenix LiveView

Hi @IwateKyle, I’m sorry to hear that you found this particular exercise so challenging. Rest assured that live_patch is covered in greater detailed later on in the book and we will update the text to let readers know.

In the meantime, here is some guidance on the solution:

  • Per the docs here (and as shown in the original question on this thread above), you can write the live_patch function call in the markup in the render function of WrongLive like this:
<%= live_patch to: Routes.live_path(@socket, __MODULE__), replace: true do %>
      <button>Try again!</button>
<%end%>

This adds a button that is wrapped in a special kind of link called a “live patch”. A “live patch” link basically re-directs to the current live view without reloading it. From the docs, if you call live_patch with the route to the current live view…

…the new state is pushed to the client, without reloading the whole page while also maintaining the current scroll position

The value of the :to key in the argument to live_patch can be any route. To specify the route of the current live view, you use: Routes.live_path(@socket, __MODULE__) or you could use Routes.live_path(@socket, PentoWeb.WrongLive), which evaluates to the same thing. The third example in the docs here is accurate https://hexdocs.pm/phoenix_live_view/Phoenix.LiveView.Helpers.html#live_patch/2-examples.

To fully get this working, you need to add this live_patch link I described above, and you need to implement a new function in your live view, a handle_params/3 function. From the docs:

When navigating to the current LiveView, Phoenix.LiveView.handle_params/3 is immediately invoked to handle the change of params and URL state.

If you follow the link to the handle_params/3 docs, you will see that it takes in three arguments: some params, the URI and the socket, and it needs to return {:noreply, socket}. If we are aiming to “reset” the game, then we should return a socket with the appropriate starting state. So something like this:

def handle_params(_params, _uri, socket) do
    {
      :noreply,
      assign(
        socket,
        score: 0,
        message: "Guess a number."
      )
    }
  end

That should do it! I hope this helps and thanks very much for your feedback.

IwateKyle

IwateKyle

Bless you Sophie. You are a super star! I appreciate your time. I’ve since moved ahead, but I’ll definitely add this to exercise. :slight_smile:

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