GObjects don't seem to provide an API for disconnecting signals, nor do so automatically on reassignment

[oezingle]

Hi All,

I'm not sure to which degree these behaviors are expected, but I've found some difficulty in connecting, and then disconnecting a signal with a Gtk.Widget. I have a feeling this extends to every GObject that implements signals

1. Using the signal assignment (widget.on_<signal> = fn) syntax does not disconnect any previous assignments. This runs contrary to any assignment logic anywhere else in lua. In my demo, this is button_1 (top button)

2. No signal disconnection methods seem to exist. I couldn't find anyhting of the sort in the guide. I checked "disconnect", "disconnect_by_func", "handler_disconnect", and "handlers_disconnect_by_func". I assume widget.on_<signal>:connect(fn) uses GObject.signal_connect(object, signal, fn) under the hood, but it's unfortunate that the memory management functions associated with signals are not exposed, as far as I can tell. In my demo I use GObject.signal_handler_disconnect(handler_id) to accomplish this, where handler_id is the return value of widget.on_<signal>:connect(fn). In my demo, this is button_2 (bottom button)

Here's the code for my demo:

local lgi = require("lgi")
local Gtk = lgi.require("Gtk", "3.0")
local GObject = lgi.GObject

-- This button demonstrates that re-assigning a signal handler doesn't disconnect the previous assignment:
local button_1 = Gtk.Button.new_with_label("I can be clicked multiple times, but I have multiple handlers")

---@diagnostic disable-next-line:duplicate-set-field
button_1.on_clicked = function ()
    print("Button 2 Click handler 1!")
end
---@diagnostic disable-next-line:duplicate-set-field
button_1.on_clicked = function ()
    print("Button 2 Click handler 2!")
end

-- This button demonstrates the difficulty in disconnecting a signal:
local button_2 = Gtk.Button.new_with_label("I can be clicked once!")

local handler_id
-- using widget.<signal>:connect from https://github.com/lgi-devs/lgi/blob/master/docs/guide.md#341-connecting-signals
handler_id = button_2.on_clicked:connect(function(widget)
    print("Button 1 Clicked!")
    widget:set_label("I can no longer be clicked!")

    do
        -- Checking for any signal disconnection methods attached to our widget:
        local widget_truncated = tostring(widget):match("^lgi.obj 0x[%w]+:([^%(]+)")
        for _, fn_name in ipairs({
            "disconnect",
            "disconnect_by_func",
            "handler_disconnect",
            "handlers_disconnect_by_func"
        }) do
            local ok, ret = pcall(function ()
                return widget.on_clicked[fn_name]
            end)

            if not ok or not ret then
                print(string.format("\t%s does not provide %q", widget_truncated, fn_name))
            end
        end
    end

    -- Ideally, I'd use
    --widget:disconnect(handler_id)
    -- as that uses the same object-oriented syntax lgi has lead me to expect
    print("Disconnecting signal using GObject")
    GObject.signal_handler_disconnect(widget, handler_id)
end)

local window = Gtk.Window {
    title = "GitHub issue demo",
    default_width = 400,
    default_height = 300,
    on_destroy = Gtk.main_quit,
    child = Gtk.VBox {
        button_1,
        button_2
    },
}

window:present()
window:show_all()

Gtk.main()

Edit: I was using widget[fn_name] which would always fail - oops! now using widget.on_clicked[fn_name]

[oezingle]

I created a pull request resolving my issues, though the code definitely needs to be cleaned up before it is merged: #334