[BUG] `Polygon`s and `Polyline`s don't update when `points` modified

[tologonkudaiberdiuulu]

What is the bug?

After adding new points to polygon, it's not updating automatically. You should explicitly add UniqueKey to Polygon widget.

How can we reproduce it?

To reproduce you can view min sample in github. To solve you can uncomment "// key: UniqueKey()," part in map_page.dart file

Do you have a potential solution?

No

Platforms

All

Severity

Obtrusive: Prevents normal functioning but causes no errors in the console

[JaffaKetchup]

This issue is occuring because the equality checking for elements is not working correctly. A temporary workaround is shown in the invalid issue https://github.com/flutter/flutter/issues/106743: use List.from to create a new list instance.

[tologonkudaiberdiuulu]

Then maybe when overriding "=" operator of Polygon object, you should check manually? Not using listEquals function.

[JaffaKetchup]

It's not due to that. Its because the list instance is shared, so the list on the oldWidget and newwidget are always the same.

[tologonkudaiberdiuulu]

I already tried to make like this

It's also not working. Only way to work is creating "mapsPolygons" variable also from new instance of List. Like this:

But it's too complicated, no?

[JaffaKetchup]

I generally wouldn't recommend doing what you're doing. Instead, use List<List<LatLng>>.map((coords) {}).toList() on the coordinates list, in the build method. This may also resolve the issue as well.

final coordinates = <List<LatLng>>[...];

// inside `build`
PolygonLayer(
    polygons: coordinates.map((c) => Polygon(points: c)).toList(),
),