A second attempt at a better Gtk API for Golang.

item.go

package main

type TodoItem struct {
	gtk.ListBoxRow

	Entry  gtk.Entry // acts as label
	Remove gtk.Button

	item string

	// local, doesn't have to do with Gtk
	todo *Todo
}

var _ Initializer = (*TodoItem)(nil)

func NewTodoItem(t *Todo, item string) {
	return &TodoItem{
		todo: t,
		item: item,
	}
}

func (t *TodoItem) Initialize() error {
	t.ListBoxRow = gtk.ListBoxRowNew()
	// SetKey allows the parent ListBox to easily differ between old and new
	// nodes. ReactJS does this:
	// https://reactjs.org/docs/reconciliation.html#keys
	t.ListBoxRow.SetKey(t.item)

	t.Entry = gtk.EntryNew()
	t.Entry.SetMargin(8)
	t.Entry.Bind(&t.item)
	t.Entry.Connect("changed", func(content string) {
		// Manually update the key as well. Can't really think of a better way
		// other than to use a Serial integer.
		// Content is just a copy of t.item's value.
		t.ListBoxRow.SetKey(content)

		// There's no need to update again here, as we're not modifying t.item.
	})

	t.Remove = gtk.ButtonNew()
	t.Remove.Connect("clicked", t.RemoveItem) // Bind(func())

	// Add containers into ListBoxRow:
	t.Add(t.Entry)
	t.Add(t.Remove)

	t.ShowAll()
	return nil
}

func (t *TodoItem) RemoveItem() {
	t.todo.remove(t.item)
	// Update, which updates the list as well.
	t.todo.Update()
}

main.go

package main

type Initializer interface {
	Initialize() error // error is only in case, gets floated up.
}

func main() {
	a := gtk.ApplicationNew("com.github.diamondburned.demo")
	w := gtk.ApplicationWindowNew(a)

	// The magic happens.
	w.Add(&Todo{})

	w.ShowAll()

	gtk.Main()
}

todo.go

package main

type Todo struct {
	gtk.Box

	Entry gtk.Entry
	Add   gtk.Button

	// local states
	ItemContainer gtk.ListBox
	Items         []*TodoItem

	// more local states
	entryText string
}

var _ Initializer = (*Todo)(nil)

func (t *Todo) Initialize() error {
	t.Box = gtk.BoxNew()

	t.Entry = gtk.EntryNew()
	t.Entry.SetMargin(10)
	t.Entry.SetMarginRight(5)

	// Bind changes the string's content with each edit.
	t.Entry.Bind(&t.entryText)

	t.Add = gtk.ButtonNew()
	t.Add.Connect("clicked", func() {
		t.add(t.entryText)
		t.entryText = ""

		// Manually update the main node. This triggers ListBox's internal
		// pointer to the slice as well, which updates the list of Todo items.
		// It will also trigger Entry and edit its content to nothing.
		t.Update()
	})

	t.ItemContainer = gtk.ListBoxNew()
	t.ItemContainer.SetMargin(10)
	t.ItemContainer.Bind(&t.Items) // allow (*gtk.ListBox).SetListCallback()

	// This is needed to be called normally in Gtk. This draft adds an extra
	// functionality of first-time calling mounted methods to populate the
	// state.
	t.ShowAll()

	return nil
}

func (t *Todo) add(item string) {
	t.Items = append(t.Items, NewTodoItem(t, item))
}

// remove is called by one of the Todos.
func (t *Todo) remove(item string) {
	for i, todo := range t.Items {
		if todo.item == item {
			t.Items = append(t.Items[:i], t.Items[i+1:]...)
			return
		}
	}
}