How do I set up a slot (event handler) that takes parameters, using gtk.go.Connect()?

Question

I am using GTK bindings for Go.

Trying to connect a gtk.RadioButton toggle signal to a function. This code works fine:

...

radioButton.Connect("toggled", doRadioToggle)

func doRadioToggle() {
    fmt.Println("toggled")
}

...

When radioButton is toggled, doRadioToggle is called - Good.

---

But I want to connect to a function that takes a parameter, for example:

func doRadioToggle(button *gtk.RadioButton) {
    fmt.Println(button.GetState())
}

The gtk.go.Connect() function has this signature:

func (v *Widget) Connect(s string, f interface{}, datas ...interface{})

Based on what I know from gtkmm, I tried code like this (the go binding has apparently greatly simplified the call to connect())

radioButton.Connect("toggled", doRadioToggle, radioButton)

The third argument passed inconnect() - radioButton - corresponding todatasin

gtk.Connect(s string, f interface{}, datas ...interface{})

which I understood to mean data arguments to be passed to the slot.

But with this code, the doRadioToggle() handler never gets called, and I immediately exit with a panic:

panic: reflect: Call using *glib.CallbackContext as type *gtk.RadioButton

My question: How do I set up slot (event handler) that takes parameters using gtk.go.Connect()?

Answer 1

Based on response from the amazing mattn on GitHub:

https://github.com/mattn/go-gtk/blob/master/example/demo/demo.go#L58

Adopted, tested and working:

import(
... 
"github.com/mattn/go-gtk/glib"
)

...

func ButtonHandler(ctx *glib.CallbackContext) {
    fmt.Printf("Button Handler: %v\n", ctx.Data().(*gtk.RadioButton).GetState())
}

aRadioButton.Connect("toggled", ButtonHandler, aRadioButton)

...

Thedatasarguments inconnect()must be passed using*glib.CallbackContext in the handler's signature, then, in the handler code, use type assertion to grab the actual arguments .

Answer 2

The documentation is not clear about how to pass additional data directly; perhaps simply use a closure instead.

https://godoc.org/github.com/mattn/go-gtk/glib#CallbackContext