GIOExample1.go

package main

import (
	"fmt"
	"image"
	"image/color"
	"os"

	"gioui.org/app"
	"gioui.org/font/gofont"
	"gioui.org/io/system"
	"gioui.org/layout"
	"gioui.org/op"
	"gioui.org/op/clip"
	"gioui.org/op/paint"
	"gioui.org/unit"
	"gioui.org/widget"
	"gioui.org/widget/material"
)

type C = layout.Context
type D = layout.Dimensions

func loop(w *app.Window) {
	th := material.NewTheme(gofont.Collection())
	var okButton, cancelButton widget.Clickable
	var ops op.Ops

	for e := range w.Events() {
		switch e := e.(type) {

		case system.DestroyEvent:
			if e.Err != nil {
				panic(e.Err)
			}
			os.Exit(0)
			return

		case system.FrameEvent:
			if okButton.Clicked() {
				fmt.Println("clicked ok")
			}
			gtx := layout.NewContext(&ops, e)
			layout.Flex{
				Axis:    layout.Vertical,
				Spacing: layout.SpaceStart,
			}.Layout(gtx,
				layout.Flexed(50,
					func(gtx C) D {
						return layout.Inset{
							Top:    unit.Dp(25),
							Bottom: unit.Dp(0),
							Right:  unit.Dp(25),
							Left:   unit.Dp(25),
						}.Layout(gtx, func(gtx C) D {
							r := image.Rectangle{Max: gtx.Constraints.Max}
							paint.FillShape(gtx.Ops, color.NRGBA{G: 255, A: 255}, clip.Rect(r).Op())
							return layout.Dimensions{Size: gtx.Constraints.Max}
						})
					},
				),
				layout.Rigid(
					func(gtx C) D {
						return layout.Inset{
							Top:    unit.Dp(25),
							Bottom: unit.Dp(25),
							Right:  unit.Dp(25),
							Left:   unit.Dp(25),
						}.Layout(gtx,
							func(gtx C) D {
								btnWidth := gtx.Px(unit.Dp(80))
								return layout.Flex{
									Alignment: layout.Middle,
									Spacing:   layout.SpaceBetween,
								}.Layout(gtx,
									layout.Rigid(func(gtx C) D {
										gtx.Constraints.Min.X = btnWidth
										return material.Button(th, &cancelButton, "Cancel").Layout(gtx)
									}),
									layout.Rigid(func(gtx C) D {
										gtx.Queue = nil // disable button
										gtx.Constraints.Min.X = btnWidth
										return material.Button(th, &okButton, "OK").Layout(gtx)
									}),
								)
							},
						)
					},
				),
			)
			e.Frame(gtx.Ops)
		}
	}
}

func main() {
	go loop(app.NewWindow(
		app.Title("Example"),
		app.Size(unit.Dp(400), unit.Dp(600)),
		app.MinSize(unit.Dp(230), unit.Dp(200)),
	))
	app.Main()
}