英文:
Fyne List widget doesn't display items correctly
问题
我正在尝试在一个listwithdata小部件中显示字母表。我正在使用自定义的可点击标签作为小部件来显示在列表中。不知何故,当小部件加载时,一切都正常显示。但是当我开始滚动时,字母开始以完全随机的顺序显示,我无法弄清楚原因。以下是一个完全可工作的代码来重现这个错误。
点击操作正常工作,并给我提供了正确的字母(不是显示的字母,而是应该显示的字母)。
我猜我一定在某个地方做错了,但我找不出问题所在。
如果有人能帮忙,将不胜感激!
英文:
I'm trying to display the alphabet in a listwithdata widget. I am using a custom clickable label as the widget to display in the list.
For some reason everything displays fine when the widget loads. But when I start scrolling the letters starts being displayed in a completely random order and I cant figure out why.
Here is a fully working code to reproduce the bug.
package main
import (
"fmt"
"fyne.io/fyne/v2"
"fyne.io/fyne/v2/app"
"fyne.io/fyne/v2/data/binding"
"fyne.io/fyne/v2/widget"
)
func makeAlphabet() []string {
var alphabet []string
for ch := 'A'; ch <= 'Z'; ch++ {
alphabet = append(alphabet, string(ch))
}
return alphabet
}
type TapLabel struct {
*widget.Label //composition
//function pointers to set to get events
OnTapped func(string)
}
func (mc *TapLabel) Tapped(pe *fyne.PointEvent) {
if mc.OnTapped != nil {
mc.OnTapped(mc.Text)
}
}
func NewTapLabel(text string, tappedLeft func(string)) *TapLabel {
return &TapLabel{widget.NewLabel(text), tappedLeft}
}
func alphabetToBrands(letter string) {
fmt.Println(letter)
}
func main() {
app := app.New()
window := app.NewWindow("tac_hub")
window.Resize(fyne.NewSize(200,200))
rawData := makeAlphabet()
data := binding.BindStringList(&rawData)
list := widget.NewListWithData(
data,
func() fyne.CanvasObject {
return NewTapLabel("template", alphabetToBrands)
},
func(i binding.DataItem, o fyne.CanvasObject) {
o.(*TapLabel).Bind(i.(binding.String))
},
)
window.SetContent(list)
window.ShowAndRun()
}
The click action works correctly and gives me the correct letter (not the one that is displayed but the one that should be displayed).
I'm guessing I must be doing something wrong somewhere but I can't figure out what.
If anyone can help it would be appreciated!
答案1
得分: 2
使用自定义小部件的解决方案:
这是基于 Fyne 的扩展小部件教程。特别是你调用了 ExtendBaseWidget
:
> ExtendBaseWidget 用于扩展小部件以利用 BaseWidget 的功能。
你仍然嵌入了 widget.Label
,但不使用指针(使用指针也可以,但文档使用的是非指针示例),这样必要的方法就会被提升到你的小部件中:
func NewTapLabel(text string, tappedLeft func(string)) *TapLabel {
label := &TapLabel{}
label.ExtendBaseWidget(label)
label.SetText(text)
label.OnTapped = tappedLeft
return label
}
然后,你需要更改更新函数,将实际的绑定字符串设置为标签的文本,而不仅仅是像在原始示例中重新绑定数据:
func(i binding.DataItem, o fyne.CanvasObject) {
s, _ := i.(binding.String).Get()
o.(*TapLabel).SetText(s)
}
至于为什么如果省略调用 ExtendBaseWidget
会出现错误,我猜测是因为缺少基本小部件的实现,而这个方法会设置它。
不使用自定义小部件的解决方案:
list := widget.NewListWithData(
data,
func() fyne.CanvasObject {
return &widget.Label{Text: "template"}
},
func(i binding.DataItem, o fyne.CanvasObject) {
o.(*widget.Label).Bind(i.(binding.String))
},
)
list.OnSelected = func(id widget.ListItemID) {
fmt.Println(rawData[id])
}
放弃你的自定义 TapLabel
,而是使用 &widget.Label{Text: "template"}
,然后使用 list.OnSelected
并在数据切片周围进行闭包,以打印被点击的项。
英文:
Solution with custom widget:
This is based on Fyne Extending Widgets tutorial. In particular you call ExtendBaseWidget
:
> ExtendBaseWidget is used by an extending widget to make use of BaseWidget functionality.
You still embed widget.Label
, but not as a pointer (using a pointer also works, but the documentation uses the non-pointer example), so that the necessary methods are promoted into your widget:
func NewTapLabel(text string, tappedLeft func(string)) *TapLabel {
label := &TapLabel{}
label.ExtendBaseWidget(label)
label.SetText(text)
label.OnTapped = tappedLeft
return label
}
And then you change the update function to set the actual bound string to the label, instead of just binding the data again as in your original example:
func(i binding.DataItem, o fyne.CanvasObject) {
s, _ := i.(binding.String).Get()
o.(*TapLabel).SetText(s)
},
As of why the bug occurs if you omit calling ExtendBaseWidget
, I suspect it's because it was missing the base widget implementation, which this method sets.
<hr>
Solution without custom widget:
list := widget.NewListWithData(
data,
func() fyne.CanvasObject {
return &widget.Label{Text: "template"}
},
func(i binding.DataItem, o fyne.CanvasObject) {
o.(*widget.Label).Bind(i.(binding.String))
},
)
list.OnSelected = func(id widget.ListItemID) {
fmt.Println(rawData[id])
}
Dropping your custom TapLabel
in favor of &widget.Label{Text: "template"}
, then to print the tapped item you use list.OnSelected
and close around the data slice.
答案2
得分: 0
看起来这里的参数 o.(*TapLabel).Bind(i.(binding.String))
在滚动操作发生时会发生变化。在该函数中添加一个日志来观察 i.(binding.String)
的值。
请查看这个示例:列表示例
英文:
Looks like the argument here o.(*TapLabel).Bind(i.(binding.String))
changes as the scroll action happens. Add a log to observe the i.(binding.String)
value in that function as you scroll
Take a look at this: list example
答案3
得分: 0
据我所见,自定义小部件的构造函数没有调用ExtendBaseWidget
,这对于正确渲染是必需的。我认为这也回答了@blackgreen的问题。
正如接受的答案中所指出的那样,您不应该使用其他小部件的构造函数嵌入它们。
英文:
As far as I can see the constructor for the custom widget did not call ExtendBaseWidget
which is required for rendering to work correctly. I think that answers @blackgreen question too.
You should not embed other widgets using their constructor as noted in the accepted answer.
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