I knew that I don't know how to deal with error returned by gotk3, so just panic.
package main
import (
"github.com/gotk3/gotk3/gtk"
"github.com/lidaobing/gtkmust"
)
func main() {
// Initialize GTK without parsing any command line arguments.
gtk.Init(nil)
// Create a new toplevel window, set its title, and connect it to the
// "destroy" signal to exit the GTK main loop when it is destroyed.
win := gtkmust.WindowNew(gtk.WINDOW_TOPLEVEL)
win.SetTitle("Simple Example")
win.Connect("destroy", func() {
gtk.MainQuit()
})
// Create a new label widget to show in the window.
l := gtkmust.LabelNew("Hello, gotk3!")
// Add the label to the window.
win.Add(l)
// Set the default window size.
win.SetDefaultSize(800, 600)
// Recursively show all widgets contained in this window.
win.ShowAll()
// Begin executing the GTK main loop. This blocks until
// gtk.MainQuit() is run.
gtk.Main()
}