How come flash messages are not propagating to the `live_component` parent?

I have an app with posts and comments, and a “Post a comment” form. The “Post a comment” form is a LiveComponent and most of the code in it has been copied from the default implementation for the way the new/update form works on default-generated index and show pages created via the generator.

However, one piece of behavior that works fine with generated index/show pages is not working for the comment form and I can’t figure out why. When a user creates a new comment, this code should trigger a flash message:

      {:ok, comment} ->
        notify_parent({:comment_saved, comment})

         |> put_flash(:info, "Comment created successfully")}

but it doesn’t.

If I instead trigger a flash message in the Post show.ex file that the comment form is rendered from, it works fine. That is, this works:

  @impl true
  def handle_info({FormComponent, {:comment_saved, comment}}, socket) do
     |> stream_insert(:comments, comment)
     |> put_flash(:info, "Comment saved successfully")}

But I’d rather the code for that flash message stay in the relevant form_component file.

The LiveComponent is invoked in the show.html.heex file like this:


If there’s any other code that would be helpful to provide to help track down why this isn’t working in this case, let me know.

The socket for the live component is different to the socket for the parent live view.

To update the live view socket you will need to send a message to the parent liveview and handle the message there to update the correct socket.

In the live component (in place of put_flash):

 send self(), {:update_flash, {:info, "Comment saved successfully"}}

In the live view:

  def handle_info({:update_flash, {flash_type, msg}}, socket) do
    update_socket = put_flash(socket, flash_type, msg)
    {:noreply, updated_socket}
1 Like

That makes sense, but if that’s true, why do flash messages work fine without that in the standard generated code?

The only obvious difference I can see is that the standard generated code is calling push_patch after the flash message is set. Does that call make a difference to how this works?

Interesting and really good post by @sevenseacat about how to update messages from a LiveComponen that maybe useful for you:


Good question - have you tried commenting out the push_patch from the generated code to see what happens?

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Yes: Phoenix.LiveView — Phoenix LiveView v0.19.4 :blush: