Empty table in received message (SOLVED)

**makorenwastaken** · July 29, 2020, 1:58pm

I’m trying to send a message to a GUI script from an enemy object with this code:

-- enemydamage.script
function on_message(self, message_id, message, sender)
    if message_id == cursor.PRESSED then
        print("Clicked!")
        msg.post("/gui#healthbars", "enemydamage", {
            currentHealth = 10,
            maxHealth = 100
        })
    end
end

I receive that message here:

-- healthbars.gui_script
function on_message(self, message_id, message, sender)
    print("Received message!")
    if message_id == hash("enemydamage") then
        print(#message)
    end
end

I get “Clicked!” and “Received message!” in the console, but also get 0 from the message table’s length. Attempting to get one of the values from that table also returns nil.

What am I doing wrong here?

**Mathias_Westerdahl** · July 29, 2020, 8:16am

#message only works if the table is “a list”, i.e. it has keys of the form 1, 2, 3, 4 etc. (starting at 1).

Try doing pprint(message) instead.

**makorenwastaken** · July 29, 2020, 8:29am

pprint is returning “{ } --[[0x10e496580]]”.

**Mathias_Westerdahl** · July 29, 2020, 8:37am

(sorry, missed that that you got a 0)

It seems strange that you would get an empty table indeed.
Are you perhaps sending this message from another place too?
Try printing the sender, to verify that it only comes from one url.

**makorenwastaken** · July 29, 2020, 8:46am

It’s printing the URL for the enemydamage script: url: [main:/enemy#enemydamage]

There’s only one enemy instance and one instance of the GUI, if that helps.

**Pkeod** · July 29, 2020, 9:13am

Can you make and post a zip of a minimally reproducible example project?

Something I prefer to use when communicating between GOs and GUIs is Broadcast

github.com

britzl/ludobits/blob/master/ludobits/m/broadcast.md

# Broadcast
Module to simplify sending of a message to multiple receivers

## Usage

	-- receiver_a.script
	local broadcast = require "ludobits.m.broadcast"

	function init(self)
		broadcast.register("foo")
	end

	function final(self)
		broadcast.unregister("foo")
	end

	function on_message(self, message_id, message, sender)
		if message_id == hash("foo") then
			-- handle message "foo"
		end

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github.com

britzl/ludobits/blob/master/ludobits/m/broadcast.lua

local M = {}

local receivers = {}

local function ensure_hash(string_or_hash)
	return type(string_or_hash) == "string" and hash(string_or_hash) or string_or_hash
end

local function url_to_key(url)
	return hash_to_hex(url.socket) .. hash_to_hex(url.path) .. hash_to_hex(url.fragment or hash(""))
end

--- Send a message to all registered receivers
-- @param message_id
-- @param message
function M.send(message_id, message)
	assert(message_id)
	local key = ensure_hash(message_id)
	if receivers[key] then
		message = message or {}

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**makorenwastaken** · July 29, 2020, 9:34am

Found the issue while trying to make that example project. I also kinda lied to you with my OP.

The original code looked like this:

-- enemydamage.script
function on_message(self, message_id, message, sender)
    if message_id == cursor.PRESSED then
        print("Clicked!")
        msg.post("/gui#healthbars", "enemydamage", {
            currentHealth = self.health,
            maxHealth = self.maxHealth
        })
    end
end

Looks like the table was empty because I was passing in a couple of nil values. It was originally not working even with raw values in the table, which is why I posted that… but whatever, it’s working now. Thanks for the help, and sorry for the confusion.