What's wrong with my Phoenix LiveView code?

Backend Developer Forum Backend Questions/Help
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1

Currently reading the book “Programming Phoenix LiveView”.
At the end of the Chapter 1, I’m trying to solve the guess game. If the user guesses the random number generated by the program the program should say Your guess: #{guess}. Correct!, but it doesn’t run that condition even if the guessed number is exactly the same as the random_number generated at the time of mount.
I’ve also added the line The randome number is <%= @random %> to see if I’m guessing the correct number.

Following is the code.

defmodule PentoWeb.WrongLive do
  use PentoWeb, :live_view

  def mount(_params, _session, socket) do
    {:ok, assign(socket, score: 0, message: "Make a guess:", time: time(), random: random())}
  end

  def render(assigns) do
    ~H"""
    <h1 class="mb-4 text-4xl font-extrabold">Your score: <%= @score %></h1>
    <h2>
      <%= @message %>
      The randome number is <%= @random %>
    </h2>
    <br/>
    <h2>
      <%= for n <- 1..10 do %>
        <.link class="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 border border-blue-700 rounded m-1" phx-click="guess" phx-value-number= {n} >
          <%= n %>
        </.link>
      <% end %>
    </h2>
    """
  end

  def time() do
    DateTime.utc_now() |> to_string()
  end

  def random() do
    Enum.random(1..10)
  end

  def handle_event("guess", %{"number" => guess}, socket) do
    message = cond do
      guess == socket.assigns.random ->
        "Your guess: #{guess}. Correct!"
      true ->
        "Your guess: #{guess}. Wrong. Guess again."
    end

    {:noreply, assign(socket, score: socket.assigns.score + 1, message: message, time: time(), random: socket.assigns.random)}
  end
end

@SophieDeBenedetto

1 Like
2

Bard said to make the handle_event like this,

  def handle_event("guess", %{"number" => guess}, socket) do
    message = cond do
      guess == socket.assigns.random ->
        "Your guess: #{guess}. Correct!"
        {:noreply, assign(socket, random: random())}
      true ->
        "Your guess: #{guess}. Wrong. Guess again."
    end

      {:noreply, assign(socket, score: socket.assigns.score + 1, message: message, time: time())}
    end

but that didn’t work either.

1 Like
3

Your guess variable in the handle_event function is a string, so guess == socket.assigns.random is comparing a string against an integer. An easy fix would be to return a string from your random/0 function.

2 Likes
4

Thank you for your reply!

It doesn’t work. I tried converting the value inside random() function to String, it didn’t work that way.
Then I converted the guess coming from the user inside the handle_event to integer before comparing it with socket.assign.random, it didn’t work again.

Right now my code is as follows,

defmodule PentoWeb.WrongLive do
  use PentoWeb, :live_view

  def mount(_params, _session, socket) do
    {:ok, assign(socket, score: 0, message: "Make a guess:", time: time(), random: random())}
  end

  def render(assigns) do
    ~H"""
    <h1 class="mb-4 text-4xl font-extrabold">Your score: <%= @score %></h1>
    <h2>
      <%= @message %>
      The randome number is <%= @random %>
    </h2>
    <br/>
    <h2>
      <%= for n <- 1..10 do %>
        <.link class="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 border border-blue-700 rounded m-1" phx-click="guess" phx-value-number= {n} >
          <%= n %>
        </.link>
      <% end %>
    </h2>
    """
  end

  def time() do
    DateTime.utc_now()
  end

  def random() do
    Enum.random(1..10)
  end

  def handle_event("guess", %{"number" => guess}, socket) do
    guess = Integer.parse(guess) |> elem(0)
    message = cond do
      guess == socket.assigns.random ->
        "Your guess: #{guess}. Correct!"
        {:noreply, assign(socket, random: random())}
      true ->
        "Your guess: #{guess}. Wrong. Guess again."
    end

      {:noreply, assign(socket, score: socket.assigns.score + 1, message: message, time: time())}
    end
  end

At this point when I click the correct option, it gives the following error,

[debug] HANDLE EVENT "guess" in PentoWeb.WrongLive
  Parameters: %{"number" => "3"}
[debug] Replied in 729µs
[error] GenServer #PID<0.505.0> terminating
** (Protocol.UndefinedError) protocol Phoenix.HTML.Safe not implemented for {:noreply, #Phoenix.LiveView.Socket<id: "phx-F5RYrXnIuZbLRwBE", endpoint: PentoWeb.Endpoint, view: PentoWeb.WrongLive, parent_pid: nil, root_pid: #PID<0.505.0>, router: PentoWeb.Router, assigns: %{message: "Make a guess:", time: ~U[2023-11-04 06:49:57.476986Z], random: 2, __changed__: %{random: true}, flash: %{}, live_action: nil, score: 0}, transport_pid: #PID<0.497.0>, ...>} of type Tuple. This protocol is implemented for the following type(s): Atom, BitString, Date, DateTime, Decimal, Float, Integer, List, NaiveDateTime, Phoenix.HTML.Form, Phoenix.LiveComponent.CID, Phoenix.LiveView.Component, Phoenix.LiveView.Comprehension, Phoenix.LiveView.JS, Phoenix.LiveView.Rendered, Time, Tuple, URI
    (phoenix_html 3.3.3) lib/phoenix_html/safe.ex:97: Phoenix.HTML.Safe.Tuple.to_iodata/1
    (pento 0.1.0) lib/pento_web/live/wrong_live.ex:12: anonymous fn/2 in PentoWeb.WrongLive.render/1
    (phoenix_live_view 0.19.5) lib/phoenix_live_view/diff.ex:363: Phoenix.LiveView.Diff.traverse/7
    (phoenix_live_view 0.19.5) lib/phoenix_live_view/diff.ex:538: anonymous fn/4 in Phoenix.LiveView.Diff.traverse_dynamic/7
    (elixir 1.15.7) lib/enum.ex:2510: Enum."-reduce/3-lists^foldl/2-0-"/3
    (phoenix_live_view 0.19.5) lib/phoenix_live_view/diff.ex:361: Phoenix.LiveView.Diff.traverse/7
    (phoenix_live_view 0.19.5) lib/phoenix_live_view/diff.ex:136: Phoenix.LiveView.Diff.render/3
    (phoenix_live_view 0.19.5) lib/phoenix_live_view/channel.ex:833: Phoenix.LiveView.Channel.render_diff/3
    (phoenix_live_view 0.19.5) lib/phoenix_live_view/channel.ex:689: Phoenix.LiveView.Channel.handle_changed/4
    (stdlib 5.1.1) gen_server.erl:1077: :gen_server.try_handle_info/3
    (stdlib 5.1.1) gen_server.erl:1165: :gen_server.handle_msg/6
    (stdlib 5.1.1) proc_lib.erl:251: :proc_lib.wake_up/3
Last message: %Phoenix.Socket.Message{topic: "lv:phx-F5RYrXnIuZbLRwBE", event: "event", payload: %{"event" => "guess", "type" => "click", "value" => %{"number" => "3"}}, ref: "13", join_ref: "11"}
State: %{socket: #Phoenix.LiveView.Socket<id: "phx-F5RYrXnIuZbLRwBE", endpoint: PentoWeb.Endpoint, view: PentoWeb.WrongLive, parent_pid: nil, root_pid: #PID<0.505.0>, router: PentoWeb.Router, assigns: %{message: "Make a guess:", time: ~U[2023-11-04 06:49:57.476986Z], random: 3, __changed__: %{}, flash: %{}, live_action: nil, score: 0}, transport_pid: #PID<0.497.0>, ...>, components: {%{}, %{}, 1}, topic: "lv:phx-F5RYrXnIuZbLRwBE", serializer: Phoenix.Socket.V2.JSONSerializer, join_ref: "11", upload_names: %{}, upload_pids: %{}}
[debug] MOUNT PentoWeb.WrongLive
  Parameters: %{}
  Session: %{"_csrf_token" => "-UTX1GiHNYDm90jd4qqktPfh"}
[debug] Replied in 104µs
1 Like
5

In case the guess was right you’re now setting the message variable to {:noreply, socket}. You need to remove that line. Also there’s no need to use cond here, just use if/else.

1 Like