省略号扩展 fyne NewVBox

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英文:

ellipsis expansion fyne NewVBox

问题

我正在尝试创建一个包含一系列按钮的Fyne垂直框,但无法弄清楚基本的机制。我认为这是一个关于Go语言的问题,而不是Fyne的问题,关于Go语言的某些东西我不太理解。

这是一个最简程序,展示了我的意思:

package main

import (
	"fmt"

	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/widget"
)

func main() {

	a := app.New()
	w := a.NewWindow("Button List")

	btn0 := widget.NewButton("button 0", func() {
		fmt.Println("Pressed 0")
	})
	btn1 := widget.NewButton("button 1", func() {
		fmt.Println("Pressed 1")
	})

	btns := []*widget.Button{btn0, btn1}

	vbox := container.NewVBox(
		// does work
		btns[0],
		btns[1],
		// doesn't work
		// btns...,
	)

	w.SetContent(
		vbox,
	)
	w.ShowAndRun()
}

我理解的是,参数btns...应该产生与参数列表btn[0],btn[1]相同的效果,但显然并不是这样。如果我注释掉以下行:

    btn[0], 
    btn[1],

并取消注释以下行:

    btns...

我会得到错误消息:

cannot use btns (type []*"fyne.io/fyne/v2/widget".Button) as type
[]fyne.CanvasObject in argument to container.NewVBox

所以,我的新手问题是:

  • 这里发生了什么,即为什么btns...不起作用?
  • 作为NewVBox的参数,我应该使用什么?
英文:

I'm trying to create a Fyne vertical box with a series of buttons but can't figure out the basic mechanism. I think this is a Go question, not a Fyne question, something I don't understand about go.

Here is a minimal program to show what I mean:

package main

import (
	"fmt"

	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/widget"
)

func main() {

	a := app.New()
	w := a.NewWindow("Button List")

	btn0 := widget.NewButton("button 0", func() {
		fmt.Println("Pressed 0")
	})
	btn1 := widget.NewButton("button 1", func() {
		fmt.Println("Pressed 1")
	})

	btns := []*widget.Button{btn0, btn1}

	vbox := container.NewVBox(
		// does work
		btns[0],
		btns[1],
		// doesn't work
		// btns...,
	)

	w.SetContent(
		vbox,
	)
	w.ShowAndRun()
}

My understanding is that the argument btns... should produce the same effect as the list of arguments btn[0], btn[1], but it apparently doesn't. If I comment out the lines

    btn[0], 
    btn[1],

and uncomment the line

    btns...

I get the error message

> cannot use btns (type []*"fyne.io/fyne/v2/widget".Button) as type
> []fyne.CanvasObject in argument to container.NewVBox

So, my newbie questions:

  • whats going on here, i.e., why doesn't btns... work?
  • what should I be using as the argument to NewVBox instead?

答案1

得分: 4

要实现你想要的效果,你需要修改*widget.Button的切片,使其成为[fyne.CanvasObject](https://pkg.go.dev/fyne.io/fyne/v2@v2.1.0#CanvasObject)的切片。

当将参数展开到可变参数中时,类型必须与可变参数期望的类型完全匹配。这意味着类型必须是接口本身,而不是实现接口的类型。

在你的情况下,以下代码将起作用:

btns := []fyne.CanvasObject{btn0, btn1}
vbox := container.NewVBox(btns...)
英文:

To do what you're wanting to do here you need to modify the slice of *widget.Button to be a slice of fyne.CanvasObject.

When spreading into a variadic parameter like this, the types have to match exactly to what the variadic parameter is expecting. This means the type needs to be the interface itself and not a type that implements the interface.

In your case, the following will work:

btns := []fyne.CanvasObject{btn0, btn1}
vbox := container.NewVBox(btns...)

huangapple
  • 本文由 发表于 2021年10月17日 12:10:38
  • 转载请务必保留本文链接:https://go.coder-hub.com/69601264.html
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