Fyne框架报错：未启动应用时访问当前应用问题求助

一直在排查该报错的原因，但始终未发现问题所在，希望能得到帮助。每次运行代码时都会抛出如下错误：

Fyne error: Attempt to access current Fyne app when none is started
go/pkg/mod/fyne.io/fyne/v2@v2.2.3/app.go:92

虽然代码可运行，但该报错始终存在。以下是代码：

// GoMark project main.go
// Version 1.3
package main

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

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

var text = widget.NewMultiLineEntry() //Text entry
var textTitle = widget.NewLabel("")
var preview = widget.NewRichTextFromMarkdown("") //Preview side
var myWindow fyne.Window
var down_dir = ""
var filePath = "" // THIS WILL NOT EDIT PRESET!!! Look further down...
var savename = ""
var savenametxt = ""
var myApp = app.New()

func main() {
    myWindow = myApp.NewWindow("GoMark 1.3")
    // - - - Text editor / Preview - - -

    textTitle.SetText("UNSAVED DOCUMENT")
    left := container.NewBorder(nil, nil, nil, nil, text)
    middle := container.NewHSplit(left, preview)
    text.OnChanged = func(string) { //When someting is written or canged in the text entry, update with this function
        preview.ParseMarkdown(text.Text)
    }
    // - - - END - - -

    // - - - TOP SECTION - - -
    //Line creation
    line := canvas.NewLine(color.Black)
    line.StrokeWidth = 4
    savename := widget.NewEntry()
    savename.SetPlaceHolder("ABC123")

    //- - - Settings toolbar - - -
    settings := widget.NewToolbar(
        widget.NewToolbarAction(theme.ContentClearIcon(), func() {
            dialog.ShowConfirm("Do you want to clear document?", "", callback, myWindow)
        }),
        widget.NewToolbarSeparator(),
        widget.NewToolbarAction(theme.FolderNewIcon(), func() {
            log.Println("Save as Doc")
            dialog.ShowFileSave(DownloadDirectory, myWindow)
        }),
        widget.NewToolbarAction(theme.DocumentSaveIcon(), func() {
            log.Println("Save Doc")

            form_savename := widget.NewFormItem("", savename)
            form := dialog.NewForm("Save Name to S:", "Save", "Cancel", []*widget.FormItem{form_savename}, func(b bool) {
                if b == true {
                    fmt.Println("Save selected")
                    savenametxt = savename.Text
                    SaveToS(myWindow)
                    savename.SetText(savenametxt)
                }
            }, myWindow)
            form.Resize(fyne.NewSize(400, 200))
            form.Show()
        }),
    )

    //Combiner
    top := container.NewBorder(nil, line, nil, settings, textTitle)
    // - - - END - - -

    //Run the main fyne window
    main := container.NewBorder(top, nil, nil, nil, middle)
    myWindow.Resize(fyne.NewSize(1200, 800))
    myWindow.SetContent(main)
    myWindow.ShowAndRun()
}

//Clear text confirmation
func callback(yes bool) {
    fmt.Println("Running Callback")
    if yes == true {
        fmt.Println("Text CLEAR")
        clean()
    } else {
        fmt.Println("Text STAY")
    }
}

//Clear text box and preview
func clean() {
    text.Text = ""
    preview.ParseMarkdown(text.Text)
    text.Refresh()
    textTitle.Text = "UNSAVED DOCUMENT"
    textTitle.Refresh()
    dialog.ShowInformation("Text has been cleared", "", myWindow)
}

//Choose a Download folder
func DownloadDirectory(savedir fyne.URIWriteCloser, err error) {
    fmt.Println("Dialog")
    fmt.Println(savedir.URI())
}

//- - - Save to S: - - -
func SaveToS(myWindow fyne.Window) {
    if runtime.GOOS == "Windows" {
        filePath = "S:\\TMP\\DocMove" //EDIT DIR PRESET FOR WINDOWS
        filePath = filePath + "\\"
    } else {
        filePath = "/mnt/s/TMP/DocMove" // EDIT DIR PRESET FOR LINUX
        filePath = filePath + "/"
    }
    fmt.Println(runtime.GOOS)
    file, errC := os.Create(filePath + savenametxt + ".md")
    if errC != nil {
        dialog.ShowError(errC, myWindow)
        fmt.Println(errC)
        return
    } else {
        _, errWriting := file.Write([]byte(text.Text))
        if errWriting != nil {
            dialog.ShowError(errWriting, myWindow)
            fmt.Println(errWriting)
            return
        } else {
            textTitle.SetText(savenametxt)
            dialog.ShowInformation("Sucess", savenametxt+" Has been saved", myWindow)
            fmt.Println(filePath + savenametxt + ".md")
        }
    }
}

报错的核心是全局Fyne组件在main函数执行前提前初始化，此时应用启动流程未完成。

Go语言中全局变量会在main函数运行前初始化，你在全局作用域创建了text、textTitle、preview这些Fyne组件，以及myApp = app.New()。当这些组件被初始化时，Fyne内部会尝试访问当前应用实例，但此时应用还未真正启动（要等到myWindow.ShowAndRun()才会启动应用循环），因此触发报错。

修复步骤： #

1. 将全局Fyne变量改为仅声明不初始化：

var text *widget.MultiLineEntry //Text entry
var textTitle *widget.Label
var preview *widget.RichText //Preview side
var myWindow fyne.Window
var down_dir = ""
var filePath = "" // THIS WILL NOT EDIT PRESET!!! Look further down...
var savename = ""
var savenametxt = ""
var myApp fyne.App

2. 在main函数内先初始化myApp，再依次创建其他组件：

func main() {
    myApp = app.New()
    myWindow = myApp.NewWindow("GoMark 1.3")
    
    // 初始化全局组件
    text = widget.NewMultiLineEntry()
    textTitle = widget.NewLabel("")
    preview = widget.NewRichTextFromMarkdown("")
    
    textTitle.SetText("UNSAVED DOCUMENT")
    // 后续原有代码保持不变...
}

这样修改后，所有Fyne组件的初始化都在应用实例创建后完成，就不会再出现该报错了。

内容的提问来源于stack exchange，提问作者TrixTec