main.go

package main

import (
	"io/ioutil"
	"os"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/dialog"
	"fyne.io/fyne/v2/layout"
	"fyne.io/fyne/v2/theme"
	"fyne.io/fyne/v2/widget"
)

// main function.
func main() {
	a := app.New()
	a.Settings().SetTheme(theme.DarkTheme())
	w := a.NewWindow("テキストエディター")
	edit := widget.NewEntry()
	edit.MultiLine = true
	sc := container.NewScroll(edit)
	inf := widget.NewLabel("information bar.")

	// new file function
	nf := func() {
		dialog.ShowConfirm("Alert", "Create New document?,", func(f bool) {
			if f {
				edit.SetText("")
				inf.SetText("create new document")
			}
		}, w)
	}

	// open file function
	of := func() {
		f := widget.NewEntry()
		dialog.ShowCustomConfirm("Open file name.", "OK",
			"Cancel", f, func(b bool) {
				if b {
					fn := f.Text + ".txt"
					ba, er := ioutil.ReadFile(fn)
					if er != nil {
						dialog.ShowError(er, w)
					} else {
						edit.SetText(string(ba))
						inf.SetText("Open from file ''" + fn + "'.'")
					}
				}
			}, w)
	}

	// save fine function
	sf := func() {
		f := widget.NewEntry()
		dialog.ShowCustomConfirm("Save file name. ", "OK",
			"Cancel", f, func(b bool) {
				if b {
					fn := f.Text + ".txt"
					er := ioutil.WriteFile(fn,
						[]byte(edit.Text),
						os.ModePerm)
					if er != nil {
						dialog.ShowError(er, w)
						return
					}
					inf.SetText("Save to file ''" + fn + "'.'")
				}

			}, w)

	}

	qf := func() {
		dialog.ShowConfirm("Alert", "Quit application?", func(f bool) {
			if f {
				a.Quit()
			}
		}, w)
	}

	tf := true

	// change theme function
	cf := func() {
		if tf {
			a.Settings().SetTheme(theme.LightTheme())
			inf.SetText("Change to Light-Theme")
		} else {
			a.Settings().SetTheme(theme.DarkTheme())
			inf.SetText("Change to Dart-Theme")
		}
		tf = !tf
	}

	// create menubar function.
	createMenubar := func() *fyne.MainMenu {
		return fyne.NewMainMenu(
			fyne.NewMenu("File",
				fyne.NewMenuItem("New", func() {
					nf()
				}),
				fyne.NewMenuItem("Open...", func() {
					of()
				}),
				fyne.NewMenuItem("Save", func() {
					sf()
				}),
				fyne.NewMenuItem("Change Theme", func() {
					cf()
				}),
				fyne.NewMenuItem("Quit", func() {
					qf()
				}),
			),
			fyne.NewMenu("File",
				fyne.NewMenuItem("Cut", func() {
					edit.TypedShortcut(
						&fyne.ShortcutCut{
							Clipboard: w.Clipboard()})
					inf.SetText("Cut text.")
				}),
				fyne.NewMenuItem("Copy", func() {
					edit.TypedShortcut(
						&fyne.ShortcutCopy{
							Clipboard: w.Clipboard()})
					inf.SetText("COPY text.")
				}),
				fyne.NewMenuItem("Paste", func() {
					edit.TypedShortcut(
						&fyne.ShortcutPaste{
							Clipboard: w.Clipboard()})
					inf.SetText("Paste text.")
				}),
			),
		)
	}

	//create toolbar function.
	createToolbar := func() *widget.Toolbar {
		return widget.NewToolbar(
			widget.NewToolbarAction(
				theme.DocumentCreateIcon(), func() {
					nf()
				}),
			widget.NewToolbarAction(
				theme.FolderOpenIcon(), func() {
					of()
				}),
			widget.NewToolbarAction(
				theme.DocumentSaveIcon(), func() {
					sf()
				}),
		)
	}

	mb := createMenubar()
	tb := createToolbar()
	w.SetMainMenu(mb)

	w.SetContent(
		fyne.NewContainerWithLayout(
			layout.NewBorderLayout(
				tb, inf, nil, nil,
			),
			tb, inf, sc,
		),
	)
	w.Resize(fyne.NewSize(300, 200))
	w.ShowAndRun()
}