Don't call OnScrolled if offset did not change

[andydotxyz]

Fixes #1868

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass. <- this is super strange... can't figure out why just yet

[andydotxyz]

I meant this to be a draft PR sorry. I cannot figure out yet why the visual tests fail just because we are not triggering on duplicate OnScroll calls

[Jacalz]

Have you managed to find the source for the error?

[andydotxyz]

Have you managed to find the source for the error?

I'm getting there. Lots of widgets just worked off this false assumption.
I have found and resolved 2 issues. At least one more remains.

[andydotxyz]

Finally got to the bottom of it :)
It was 2 items in general

*) Calling Scroller.Refresh() no longer calls OnScrolled, so we may have to refresh the content directly if required
*) The setting of Scroller.Offset and then calling Refresh() does not call OnScrolled which makes sense. It previously did.

[Jacalz]

Hmm, I think there might be something wrong here. When adding a few more tabs to the DocTabs in fyne_demo, the scroller jumps back to the start after a while of dragging it to the right.

I would go about replicating it like this:

• Go to the DocTabs section in fyne_demo.
• Press the "+" button to add a few tabs and thus get a scroller.
• Grab hold of the scroller with the mouse and drag it to the right.
• About 2/3 on the way to the right, the scroller jumps back to the start again.

[andydotxyz]

Hmm, I think there might be something wrong here. When adding a few more tabs to the DocTabs in fyne_demo, the scroller jumps back to the start after a while of dragging it to the right.

This is a good catch thanks @Jacalz, however the issue is on develop too, so not part of the changes here.

[Jacalz]

Hmm, I think there might be something wrong here. When adding a few more tabs to the DocTabs in fyne_demo, the scroller jumps back to the start after a while of dragging it to the right.

This is a good catch thanks @Jacalz, however the issue is on develop too, so not part of the changes here.

Are you sure? I tested on develop and couldn't quite replicate it. I'll have to try again, I guess.

[andydotxyz]

Are you sure? I tested on develop and couldn't quite replicate it. I'll have to try again, I guess.

Quite sure - it seems to glitch when it's about to show the selected tab when scrolling.

[Jacalz]

You are entirely correct. Sorry for the fuss.

The base branch was changed.

[andydotxyz]

Not a problem thanks @Jacalz.
I decided that this was a behaviour change so did not belong on a bugfix release (given the changes we had to make internally).
If you would be OK to re-approve with this change I would be appreciative :)

[Jacalz]

Looks good twice :)