Concurrent window modification v.2 (with net/http)

multiwindow.go

package main

import (
	"fmt"
	"github.com/lxn/walk"
	. "github.com/lxn/walk/declarative"
	"io"
	"io/ioutil"
	"net/http"
)

var mainWindow *walk.MainWindow

func main() {
	_, err := MainWindow{
		AssignTo: &mainWindow,
		Title:    "Main Window",
		MinSize:  Size{400, 300},
		Layout:   VBox{},
		Children: []Widget{
			Label{Text: "something in main window"},
			PushButton{
				Text: "Do progress",
				OnClicked: func() {
					go askDialog()
				},
			},
		},
	}.Run()
	if err != nil {
		fmt.Println(err)
	}
}
func askDialog() {
	var dialog *walk.Dialog
	var acceptPB, cancelPB *walk.PushButton
	_, err := Dialog{
		AssignTo:      &dialog,
		Title:         "Do you want some progress?",
		DefaultButton: &acceptPB,
		CancelButton:  &cancelPB,
		MinSize:       Size{300, 100},
		Layout:        HBox{},
		Children: []Widget{
			PushButton{
				AssignTo: &acceptPB,
				Text:     "Yes",
				OnClicked: func() {
					dialog.Accept()
					go doProgress()
				},
			},
			PushButton{
				AssignTo:  &cancelPB,
				Text:      "No",
				OnClicked: func() { dialog.Cancel() },
			},
		},
	}.Run(mainWindow)
	if err != nil {
		fmt.Println(err)
	}
}
func doProgress() {
	var dialog *walk.Dialog
	var progressBar *walk.ProgressBar
	err := Dialog{
		AssignTo: &dialog,
		Title:    "Progress dialog",
		MinSize:  Size{300, 200},
		Layout:   VBox{},
		Children: []Widget{
			ProgressBar{AssignTo: &progressBar},
		},
	}.Create(mainWindow)
	if err != nil {
		fmt.Println(err)
		return
	}
	dialog.Starting().Attach(func() {
		go progressWorker(dialog, progressBar)
	})
	dialog.Run()
}
func progressWorker(dialog *walk.Dialog, progressBar *walk.ProgressBar) {
	defer dialog.Synchronize(func() {
		dialog.Close(0)
	})

	resp, err := http.Get("http://ipv4.download.thinkbroadband.com/5MB.zip")
	if err != nil {
		return
	}
	defer resp.Body.Close()
	length := resp.ContentLength
	mainWindow.Synchronize(func() {
		mainWindow.ProgressIndicator().SetTotal(uint32(length))
	})
	dialog.Synchronize(func() {
		progressBar.SetRange(0, int(length))
	})
	copyBufCallback(ioutil.Discard, resp.Body, func(n int64) {
		fmt.Println("progress", n)
		mainWindow.Synchronize(func() {
			if err := mainWindow.ProgressIndicator().SetCompleted(uint32(n)); err != nil {
				fmt.Println(err)
			}
		})
		dialog.Synchronize(func() {
			progressBar.SetValue(int(n))
		})

	})
	fmt.Println("done")
}
func copyBufCallback(dst io.Writer, src io.Reader, callback func(int64)) (written int64, err error) {

	buf := make([]byte, 32*1024)

	for {
		nr, er := src.Read(buf)
		if nr > 0 {
			nw, ew := dst.Write(buf[0:nr])
			if nw > 0 {
				written += int64(nw)
				callback(written)
			}
			if ew != nil {
				err = ew
				break
			}
			if nr != nw {
				err = io.ErrShortWrite
				break
			}
		}
		if er != nil {
			if er != io.EOF {
				err = er
			}
			break
		}
	}
	return written, err
}