focusable_part.go

// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gxui

// Focusable is the optional interface implmented by controls that have the ability to acquire focus.
// A control with focus will receive keyboard input first.
type Focusable interface {
	Control

	// IsFocusable returns true if the control is currently in a state where it can acquire focus.
	IsFocusable() bool

	// HasFocus returns true when the control has focus.
	HasFocus() bool

	// GainedFocus is called when the Focusable gains focus.
	// This method is called by the FocusManager should not be called by the user.
	GainedFocus()

	// LostFocus is called when the Focusable loses focus.
	// This method is called by the FocusManager should not be called by the user.
	LostFocus()

	// OnGainedFocus subscribes f to be called whenever the control gains focus.
	OnGainedFocus(callback func()) EventSubscription

	// OnLostFocus subscribes f to be called whenever the control loses focus.
	OnLostFocus(callback func()) EventSubscription
}

type FocusablePart struct {
	onGainedFocus Event
	onLostFocus   Event
	hasFocus      bool
	focusable     bool
}

func (f *FocusablePart) Init() {
	f.focusable = true
}

// gxui.Control compliance
func (f *FocusablePart) IsFocusable() bool {
	return f.focusable
}

func (f *FocusablePart) HasFocus() bool {
	return f.hasFocus
}

func (f *FocusablePart) SetFocusable(bool) {
	f.focusable = true
}

func (f *FocusablePart) OnGainedFocus(callback func()) EventSubscription {
	if f.onGainedFocus == nil {
		f.onGainedFocus = CreateEvent(f.GainedFocus)
	}

	return f.onGainedFocus.Listen(callback)
}

func (f *FocusablePart) OnLostFocus(callback func()) EventSubscription {
	if f.onLostFocus == nil {
		f.onLostFocus = CreateEvent(f.LostFocus)
	}

	return f.onLostFocus.Listen(callback)
}

func (f *FocusablePart) GainedFocus() {
	f.hasFocus = true

	if f.onGainedFocus != nil {
		f.onGainedFocus.Emit()
	}
}

func (f *FocusablePart) LostFocus() {
	f.hasFocus = false

	if f.onLostFocus != nil {
		f.onLostFocus.Emit()
	}
}