当相关变量被修改时，为什么dart对象被修改?

Question

我想在Flutter Map ('package:flutter_map/flutter_map.dart')上显示标记

但是当我添加一个时，所有的映射标记都使用相同的参数。

当用户单击地图时，将打开一个弹出窗口，其中包含用于定义标记属性的字段。

这些字段值与类变量相关联。

是因为Marker构建器使用原始变量的指针而不是它们的值吗?

还是因为Dart把基本类型理解为对象?

import 'package:flutter/material.dart';
import 'package:flutter_map/flutter_map.dart';
import 'package:latlong2/latlong.dart';
import 'package:positioned_tap_detector_2/positioned_tap_detector_2.dart';
///
/// Widget that allows display intervention
///
class DisplayIntervention extends StatefulWidget {
const DisplayIntervention({Key? key}) : super(key: key);
@override
_DisplayInterventionState createState() => _DisplayInterventionState();
}
class _DisplayInterventionState extends State<DisplayIntervention> {
// Initialize map controller
late final MapController mapController;
// Size of the left panel
final int leftPaneProportion = 20;
// Map settings
List<Marker> map_markers = [];
List<Map> availableColors = [
{'name': 'Red', 'value': Colors.red},
{'name': 'Green', 'value': Colors.green},
{'name': 'Blue', 'value': Colors.blue},
{'name': 'Black', 'value': Colors.black},
];
// Map capture (start capture many points)
bool mapCapture = false;
// History of taps
List<LatLng> tapHistory = [];
// ---- END DRAWER SECTION ----- //
// ---- START NEW MARKER SECTION ----- //
final _markerFormKey = GlobalKey<FormState>();
String _markerLabelController = "";
IconData _markerTypeController = Icons.directions_car;
int _markerRotationController = 0;
double _markerSizeController = 30.0;
Color _markerColorController = Colors.red;
List<Map> availableVehicles = [
{'name': 'Car', 'value': Icons.directions_car},
{'name': 'Truck', 'value': Icons.local_shipping},
];
// ---- END NEW MARKER SECTION ----- //

@override
void initState() {
super.initState();
mapController = MapController();
}
void _handleTap(TapPosition tapPosition, LatLng latlng) {
tapHistory.add(latlng);
openMarkerPopup();
}
void computeMarker(){
print("Add new marker");
map_markers.add(
Marker(
width: _markerSizeController,
height: _markerSizeController,
point: tapHistory.last,
builder: (ctx) =>
Container(
child: Icon(_markerTypeController, color: _markerColorController, size: _markerSizeController),
),
));
setState(() {
map_markers;
});
}
openMarkerPopup(){
showDialog(context: context, builder: (BuildContext context) {
return AlertDialog(
scrollable: true,
title: Text('Add marker'),
content: Padding(
padding: const EdgeInsets.all(8.0),
child: Form(
key: _markerFormKey,
child: Column(
children: <Widget>[
TextFormField(
initialValue: _markerLabelController,
onChanged: (value) {
_markerLabelController = value;
},
decoration: const InputDecoration(
labelText: 'Label',
icon: Icon(Icons.abc_rounded),
),
),
DropdownButtonFormField(
decoration: const InputDecoration(
icon: Icon(Icons.border_color),
),
value: _markerTypeController,
items: availableVehicles.map((map) {
return DropdownMenuItem(
child: Text(map['name']),
value: map['value'],
);
}).toList(),
onChanged: (value) {
setState(() {
if (value != null){
_markerTypeController = value as IconData;
}
});
},
),
DropdownButtonFormField(
decoration: const InputDecoration(
icon: Icon(Icons.brush_rounded),
),
value: _markerColorController,
items: availableColors.map((map) {
return DropdownMenuItem(
child: Text(map['name']),
value: map['value'],
);
}).toList(),
onChanged: (value) {
setState(() {
if (value != null){
_markerColorController = value as Color;
}
});
},
),
TextFormField(
initialValue: _markerSizeController.toString(),
keyboardType: TextInputType.number,
onChanged: (value) {
_markerSizeController = double.parse(value);
},
decoration: const InputDecoration(
labelText: 'Size',
icon: Icon(Icons.expand_more),
),
),
TextFormField(
initialValue: _markerRotationController.toString(),
keyboardType: TextInputType.number,
onChanged: (value) {
_markerRotationController = int.parse(value);
},
decoration: const InputDecoration(
labelText: 'Angle',
icon: Icon(Icons.zoom_in_rounded),
),
)
],
),
),
),
actions: [
ElevatedButton(
child: Text("Back"),
onPressed: () {
Navigator.of(context).pop();
}),
ElevatedButton(
child: Text("Valid"),
onPressed: () {
computeMarker();
Navigator.of(context).pop();
}),
],
);
});
}
@override
Widget build(BuildContext context) {
return Flex(
direction: Axis.horizontal,
children: [
Flexible(
flex: leftPaneProportion,
child: Container(
color: Colors.white,
child: Scaffold(
resizeToAvoidBottomInset: true,
body: ListView(
padding: EdgeInsets.only(
bottom: MediaQuery.of(context).viewInsets.bottom),
children: const <Widget>[
Card(
child: ListTile(
title: Text("Debug"),
trailing: Icon(
Icons.arrow_circle_right_outlined))),
],
))),
),
Flexible(
flex: 100 - leftPaneProportion,
child: FlutterMap(
mapController: mapController,
options: MapOptions(
center: LatLng(48.117266, -1.6777926),
zoom: 10,
onTap: _handleTap
),
layers: [
MarkerLayerOptions(
markers: map_markers
),
],
children: <Widget>[
TileLayerWidget(
options: TileLayerOptions(
urlTemplate:
'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png',
subdomains: ['a', 'b', 'c'],
),
),
],
),
),
],
);
}
}

Answer 1

问题来自于标记生成器

通过直接给出全局变量，构建器使用指针。

而通过中间变量传递值，问题就解决了。