Minimal app to reproduce a mem leak when loading image files to Fyne. See https://github.com/fyne-io/fyne/issues/348

main.go

package main

import (
	"flag"
	"log"
	"time"

	"net/http"
	_ "net/http/pprof"

	"fyne.io/fyne"
	"fyne.io/fyne/app"
	"fyne.io/fyne/canvas"
	"fyne.io/fyne/layout"
	"fyne.io/fyne/widget"
)

// main initializes a fyne app containing a single image which it reloads at 5s intervals
func main() {
	// serve pprof
	go func() {
		log.Println(http.ListenAndServe("localhost:6060", nil))
	}()
	// define and parse command line flags
	flag.Parse()
	args := flag.Args()
	if len(args) != 1 {
		log.Fatal("One filepath is the only allowed argument")
	}
	graphWidgets.graphFilePath = args[0]

	// initialize the app with our custom theme.
	a := app.New()

	// the top-level (and so far the only) window
	w := a.NewWindow("MemLeak")

	w.SetContent(widget.NewVBox(
		graphPanel(),
	))

	// Launch update tasks
	go graphUpdater()

	// Display and run the app
	w.ShowAndRun()
}

var graphWidgets struct {
	graphBox      *widget.Box
	container     *fyne.Container
	graph         *canvas.Image
	graphFilePath string
}

// graphPanel creates the graph Panel that fills the entire window below the
// header and menu bar
func graphPanel() *widget.Box {
	var err error
	graphWidgets.graph, err = getGraph(graphWidgets.graphFilePath)
	if err != nil {
		log.Fatal("can't load graph")
	}

	// force fit to bottom 2/3 of Pi touchscreen
	graphWidgets.container = fyne.NewContainerWithLayout(layout.NewFixedGridLayout(fyne.NewSize(800, 320)), graphWidgets.graph)
	graphWidgets.graphBox = widget.NewHBox(graphWidgets.container)
	return graphWidgets.graphBox
}

// graphUpdater reloads the graph every 5 seconds
func graphUpdater() {
	for {
		time.Sleep(5 * time.Second)

		newgraph, err := getGraph(graphWidgets.graphFilePath)
		if err != nil {
			log.Fatal("getGraph failed")
		}
		graphWidgets.container.Objects[0] = newgraph
		graphWidgets.container.Refresh()
		graphWidgets.graphBox.Refresh()
	}
}

// getGraph returns a canvas image of a graph
func getGraph(fpath string) (img *canvas.Image, err error) {
	img = canvas.NewImageFromFile(fpath)
	img.SetMinSize(fyne.NewSize(800, 320)) // force fit to width and 1/4 height of Pi touchscreen
	return
}