gotk3，带有自定义小部件的笔记本附件，并将其取回

Question

I have this summarized code to display tabs in a notebook in Gtk. Basically, I have created a custom struct with a embedded label, that is added to the notebook. After that, I want to get back that custom widget, but I get a Invalid type assertion. I have read a lot about structs and interfaces, but I can't get it to work.

package main

import "github.com/gotk3/gotk3/gtk"

type NotebookPage struct {
    gtk.Label
}


func main() {

    gtk.Init(nil)

    win, _ := gtk.WindowNew(gtk.WINDOW_TOPLEVEL)

    notebook, _ := gtk.NotebookNew()
    win.Add(notebook)

    content1, _ := gtk.LabelNew("Content 1")
    page1 := NotebookPage{Label: *content1}
    label1, _ := gtk.LabelNew("Label 1")
    notebook.AppendPage(&page1, label1)

    content2, _ := gtk.LabelNew("Content 2")
    page2 := NotebookPage{Label: *content2}
    label2, _ := gtk.LabelNew("Label 2")
    notebook.AppendPage(&page2, label2)

    win.ShowAll()
    win.Connect("destroy", func() {
        gtk.MainQuit()
    })

    backwidget1, _ := notebook.GetNthPage(0)
    backpage1, _ := backwidget1.(*NotebookPage)

    gtk.Main()

}

Answer 1

Looks like your problem is here on line 35 as the message says:

backpage1, _ := backwidget1.(*NotebookPage)

notebook.GetNthPage returns a *Widget, *NotebookPage is not a *Widget, so you're not allowed to cast to it. If the function didn't return a concrete type (if it returned the same IWidget interface), and if it didn't roundtrip through gtk C libraries, you could do this.

As it is if you want to get your custom widget back you probably need to get at the underlying gtk widget or serialisation (which presumably stores your custom label), extract the label and build a new NotebookPage.

So you need something like :

func NewNotebookPage(widget *Widget) {
   return &NotebookPage{Label: widget.GetLabelSomehow()}
}

It looks like Label is also a widget :) This is painful because it's trying to work with C++ inheritance in Go. You'll have to find out how to unfreeze your label from the widget.C.GtkWidget