Fix #629 | Reload map if options changed for overrideTilesWhenUrlChanges

[Xennis]

The option overrideTilesWhenUrlChanges currently only works if the URL
template changes but not if the options change.

For example:

TileLayerOptions(
  urlTemplate: 'https://api.mapbox.com/styles/v1/mapbox/{id}/tiles/{z}/{x}/{y}',
  additionalOptions: <String, String>{
    'id': mapboxStyle,
  },

If the value of id (here the Mapbox layer style, e.g. streets, satellite, etc.)
changes the option overrideTilesWhenUrlChanges should override the tiles as well.

[maRci002]

This isn't perfect:

      final oldOptions = oldWidget.options.additionalOptions;
      final newOptions = options.additionalOptions;

      if (oldUrl != newUrl || oldOptions != newOptions) {

When you decalre every time a new HashMap they won't be equal, see

  additionalOptions: <String, String>{
    'id': mapboxStyle,
  },

Just see this: print({'x': 1} != {'x': 1} ); you would think this will print false because they are equals, however it will print true, so in this case oldOptions != newOptions will always evaluate to true which will reload tiles unnecessarily.

On the other hand if you cache additionalOptions in a Stateful widget and later you put / change a parameter in it then I would assume TileLayer would detects changes and map will reload tiles, however this won't happen, see:

class _HomePageState extends State<HomePage> {
  final params = <String, String>{
    'id': 'myStyle',
  };

  void onEvent() {
    setState(() {
      params['id'] = 'myStyle2';
    });
  }

  Widget build(BuildContext context) {
...
                  TileLayerOptions(
                    urlTemplate: 'https://api.mapbox.com/styles/v1/mapbox/{id}/tiles/{z}/{x}/{y}',
                    additionalOptions: params,
                  )
...

If an event calls onEvent() method, then it will change param, however TileLayer has the same instance so replace will affect that HashMap too, so they will be always equals, see:

  var a = {'x': 1};
  a['x'] = 2;
  
  print(a != a);

It will print false, however I wanted to reload tiles because one param changed.

[Xennis]

Dear @maRci002 thanks for your detailed feedback. What do you recommend to fix this issue? Would using MapEquality help here?

[maRci002]

Yes you can use it, however there are still problems if programmer using explicit null value for additionalOptions.

  print((const MapEquality()).equals({'x': 1}, {'x': 1})); // true
  print((const MapEquality()).equals(null, {'x': 1})); // false !

So in TileLayerOptions change this line this.additionalOptions = const <String, String>{}, to Map<String, String> additionalOptions, and add this line to initializer list: additionalOptions = additionalOptions ?? const <String, String>{}, so now you make sure there isn't any null values and MapEquality will be fine. Note, this won't handle if you cache HashMap and change value inside it.

You have to handle updates on Map, so this case:
In initializer list you should use this line:

additionalOptions = additionalOptions == null
    ? const <String, String>{}
    : Map.from(additionalOptions), // copy Map, so we can safely compare old and new Map inside didUpdateWidget with MapEquality

[Xennis]

Hey @maRci002 great thanks for your help. I adopted the MR accordingly.

[maRci002]

LGTM