diff --git a/example/main.go b/example/main.go
index 2a60cec1c..332a992ed 100644
--- a/example/main.go
+++ b/example/main.go
@@ -2,7 +2,6 @@ package main
 
 import (
 	"github.com/hajimehoshi/go-ebiten/graphics"
-	"github.com/hajimehoshi/go-ebiten/ui"
 	"github.com/hajimehoshi/go-ebiten/ui/cocoa"
 	"image"
 	_ "image/png"
@@ -36,15 +35,12 @@ func main() {
 	const fps = 60
 	const title = "Ebiten Demo"
 
-	type UI interface {
-		ui.UI
-		graphics.TextureFactory
-	}
-	var u UI = cocoa.NewUI()
-	window := u.CreateWindow(screenWidth, screenHeight, screenScale, title)
+	ui := cocoa.UI()
+	textureFactory := cocoa.TextureFactory()
+	window := ui.CreateWindow(screenWidth, screenHeight, screenScale, title)
 
-	textureCreated := u.TextureCreated()
-	renderTargetCreated := u.RenderTargetCreated()
+	textureCreated := textureFactory.TextureCreated()
+	renderTargetCreated := textureFactory.RenderTargetCreated()
 	
 	for tag, path := range TexturePaths {
 		tag := tag
@@ -54,7 +50,7 @@ func main() {
 			if err != nil {
 				panic(err)
 			}
-			u.CreateTexture(tag, img)
+			textureFactory.CreateTexture(tag, img)
 		}()
 	}
 
@@ -62,7 +58,7 @@ func main() {
 		tag := tag
 		size := size
 		go func() {
-			u.CreateRenderTarget(tag, size.Width, size.Height)
+			textureFactory.CreateRenderTarget(tag, size.Width, size.Height)
 		}()
 	}
 
@@ -103,7 +99,7 @@ func main() {
 	}()
 
 	for {
-		u.PollEvents()
+		ui.PollEvents()
 		select {
 		default:
 			window.Draw(func(actualCanvas graphics.Canvas) {
diff --git a/ui/cocoa/texture_factory.go b/ui/cocoa/texture_factory.go
index 7946e65d3..3f9c3f0ae 100644
--- a/ui/cocoa/texture_factory.go
+++ b/ui/cocoa/texture_factory.go
@@ -50,6 +50,6 @@ func (t *textureFactory) useContext(f func()) {
 	<-t.funcsDone
 }
 
-func (t *textureFactory) createWindow(ui *UI, width, height, scale int, title string) *Window {
+func (t *textureFactory) createWindow(ui *cocoaUI, width, height, scale int, title string) *Window {
 	return runWindow(ui, width, height, scale, title, t.sharedContext)
 }
diff --git a/ui/cocoa/ui.go b/ui/cocoa/ui.go
index 7437286af..9bfff9124 100644
--- a/ui/cocoa/ui.go
+++ b/ui/cocoa/ui.go
@@ -14,40 +14,55 @@ import (
 	"image"
 )
 
-type UI struct {
+type cocoaUI struct {
 	textureFactory *textureFactory
 	graphicsDevice *opengl.Device
 }
 
-var currentUI *UI
+var currentUI *cocoaUI
 
-func NewUI() *UI {
+func getCurrentUI() *cocoaUI {
 	if currentUI != nil {
-		panic("UI can't be duplicated.")
+		return currentUI
 	}
-	u := &UI{}
+
+	currentUI = &cocoaUI{}
 
 	C.StartApplication()
 
-	u.textureFactory = runTextureFactory()
-	u.textureFactory.useContext(func() {
-		u.graphicsDevice = opengl.NewDevice()
+	currentUI.textureFactory = runTextureFactory()
+	currentUI.textureFactory.useContext(func() {
+		currentUI.graphicsDevice = opengl.NewDevice()
 	})
 
-	currentUI = u
-
-	return u
+	return currentUI
 }
 
-func (u *UI) CreateWindow(width, height, scale int, title string) ui.Window {
+func UI() ui.UI {
+	return getCurrentUI()
+}
+
+func TextureFactory() graphics.TextureFactory {
+	return getCurrentUI()
+}
+
+func (u *cocoaUI) CreateWindow(width, height, scale int, title string) ui.Window {
 	return u.textureFactory.createWindow(u, width, height, scale, title)
 }
 
-func (u *UI) PollEvents() {
+func (u *cocoaUI) PollEvents() {
 	C.PollEvents()
 }
 
-func (u *UI) CreateTexture(tag interface{}, img image.Image) {
+func (u *cocoaUI) TextureCreated() <-chan graphics.TextureCreatedEvent {
+	return u.textureFactory.TextureCreated()
+}
+
+func (u *cocoaUI) RenderTargetCreated() <-chan graphics.RenderTargetCreatedEvent {
+	return u.textureFactory.RenderTargetCreated()
+}
+
+func (u *cocoaUI) CreateTexture(tag interface{}, img image.Image) {
 	go func() {
 		var id graphics.TextureId
 		var err error
@@ -63,7 +78,7 @@ func (u *UI) CreateTexture(tag interface{}, img image.Image) {
 	}()
 }
 
-func (u *UI) CreateRenderTarget(tag interface{}, width, height int) {
+func (u *cocoaUI) CreateRenderTarget(tag interface{}, width, height int) {
 	go func() {
 		var id graphics.RenderTargetId
 		var err error
@@ -78,11 +93,3 @@ func (u *UI) CreateRenderTarget(tag interface{}, width, height int) {
 		u.textureFactory.notifyRenderTargetCreated(e)
 	}()
 }
-
-func (u *UI) TextureCreated() <-chan graphics.TextureCreatedEvent {
-	return u.textureFactory.TextureCreated()
-}
-
-func (u *UI) RenderTargetCreated() <-chan graphics.RenderTargetCreatedEvent {
-	return u.textureFactory.RenderTargetCreated()
-}
diff --git a/ui/cocoa/window.go b/ui/cocoa/window.go
index 2b049a17d..245e23d46 100644
--- a/ui/cocoa/window.go
+++ b/ui/cocoa/window.go
@@ -21,7 +21,7 @@ import (
 )
 
 type Window struct {
-	ui           *UI
+	ui           *cocoaUI
 	screenWidth  int
 	screenHeight int
 	screenScale  int
@@ -35,7 +35,7 @@ type Window struct {
 
 var windows = map[unsafe.Pointer]*Window{}
 
-func runWindow(ui *UI, width, height, scale int, title string, sharedContext unsafe.Pointer) *Window {
+func runWindow(ui *cocoaUI, width, height, scale int, title string, sharedContext unsafe.Pointer) *Window {
 	w := &Window{
 		ui:           ui,
 		screenWidth:  width,
@@ -134,4 +134,5 @@ func ebiten_WindowClosed(nativeWindow unsafe.Pointer) {
 	w := windows[nativeWindow]
 	w.closed = true
 	w.notifyWindowClosed(ui.WindowClosedEvent{})
+	delete(windows, nativeWindow)
 }