Bug in Range() implementation?

[rtrzebinski]

Description:

I'm having a issue with the following code:

app.Range(h.rows).Slice(func(i int) app.UI {
  return &h.rows[i]
}),

It works fine when the component is loaded for the first time, but not when the slice and range needs to be updated.

On rebuilding the underlying slice with data from API call, the UI behaves incorrectly.

I tried manually running component.Update - did not help.

The only work around is reloading the page with ctx.Reload() but it's doing an ugly page refresh, and it's not a solution really.

Steps to reproduce:

git clone git@github.com:rtrzebinski/simple-memorizer-4.git
git checkout 58475e1c1171863229ff0de07d7f9dbb4c2c8bd4
make dev
make run
open http://localhost:8000/exercises

Add exercises: (question / answer):

11 / 11
22 / 22
33 / 33
44 / 44

(in order to retry with a fresh database simply run make dev && make run again and refresh the page)

Expected result:

Exercises will appear on the list as they are added.

No manual page reload is needed to display them properly.

Actual result:

Only 11 / 11 (first one added) keeps being duplicated, regardless of the following inputs:

Where is the code?

Range -> https://github.com/rtrzebinski/simple-memorizer-4/blob/58475e1c1171863229ff0de07d7f9dbb4c2c8bd4/internal/frontend/components/exercises.go#L40

Update trigger -> https://github.com/rtrzebinski/simple-memorizer-4/blob/58475e1c1171863229ff0de07d7f9dbb4c2c8bd4/internal/frontend/components/exercises.go#L71

Actual UI update -> https://github.com/rtrzebinski/simple-memorizer-4/blob/58475e1c1171863229ff0de07d7f9dbb4c2c8bd4/internal/frontend/components/exercises.go#L89

[maxence-charriere]

Can you provide the ExerciseRow component code too ?

[rtrzebinski]

Of course:

type ExerciseRow struct {
	app.Compo

	exercise models.Exercise
}

// The Render method is where the component appearance is defined.
func (h *ExerciseRow) Render() app.UI {
	return app.Tr().Style("border", "1px solid black").Body(
		app.Td().Style("border", "1px solid black").Body(
			app.Text(h.exercise.Question),
		),
		app.Td().Style("border", "1px solid black").Body(
			app.Text(h.exercise.Answer),
		),
	)
}

https://github.com/rtrzebinski/simple-memorizer-4/blob/58475e1c1171863229ff0de07d7f9dbb4c2c8bd4/internal/frontend/components/exercise_row.go

@maxence-charriere

[oderwat]

Please try:

app.Range(h.rows).Slice(func(i int) app.UI {
  return h.rows[i].Render()
}),

@maxence-charriere I think this is related to the problem from #767, which is still not fixed (even if it needs another way to fix it than his method).

[rtrzebinski]

@oderwat This helped thank you so much! It would be good to document that :)

[oderwat]

@rtrzebinski please open the issue again. I am not positive, that this is a "good" way to solve it and has no unwanted side effects. I think when doing it like this you skip the "OnMount" on those components and that is not really how it should work.

Likewise, I wanted @maxence-charriere to chime in on that for some time already. I think there has definitely something to be changed.

[maxence-charriere]

Try to export the exercise field in the ExerciseRow component. I think the problem here is that there is nothing to compare to trigger a diff.

exercise => Exercise

[rtrzebinski]

Re-opening the issue as requested by @oderwat

@maxence-charriere I tried that - making ExerciseRow.Exercise exported (capital letter) indeed improved adding new rows, however without the Render() in:

				app.Range(h.rows).Slice(func(i int) app.UI {
					if h.rows[i] != nil {
						return h.rows[i].Render()
					}
					return nil
				}),

It was messing up indexed making deleting and display messed up again, so I'll stick with the Render() solution as it works well.

Please let me know if you need some more examples / steps to reproduce, I am happy to provide these.

[gepengscu]

app.Range(h.rows).Slice(func(i int) app.UI {
  return h.rows[i].Render()
}),

I avoid the "Bug" in the same way.
Never save ui in slice.
Just save nessary data in slice and render ui with data in slice.

type tabs struct{
  app.Compo
  items []*Item
}

type Item struct{
  Key string
  Label string
}
func (this *tabs) Render() app.UI {  
  return app.Div().
      Body(
        app.Range(this.items).Slice(
	   func(i int) app.UI {
	      return this.renderTab(this.items[i])
	   }))
}

func (this *tabs) renderTab(item *Item) app.UI {  
  return app.Text(item.Label).
    OnClick(this.onCloseTab(item), item.Key)
}

func (this *tabs) onCloseTab(item *Item) app.EventHandler {
  return func(ctx app.Context, e app.Event) {  
    this.items = removeItemInSlice(this.items, item)
  }
}

[oderwat]

Never save ui in slice.

This would mean you can't use a component in a slice and this would mean that there is something seriously missing in Go-App. What do you think @maxence-charriere