how to pass argument to a final variable in flutter - flutter

Question

I have the following code and could not figure out what is the problem.
I want to pass the Bluetooth device to the container in the class DeviceData and this class returns the container. I am beginner in Flutter and when I read the documentation could not understand what they are talking about.
But the first problem is
Can't define the 'const' constructor because the field 'uppersection' is initialized with a non-constant value. Try initializing the field to a constant value, or removing the keyword 'const' from the
and then device cannot be accessed:
The instance member 'device' can't be accessed in an initializer. Try replacing the reference to the instance member with a different expression
class DeviceData extends StatelessWidget {
const DeviceData({Key key, this.device}) : super(key: key);
final BluetoothDevice device;
final uppersection = new Container(
child: Row(
children: <Widget>[
StreamBuilder<BluetoothDeviceState>(
stream: device.state,
initialData: BluetoothDeviceState.connecting,
builder: (c, snapshot) => ListTile(
leading: (snapshot.data == BluetoothDeviceState.connected)
? Icon(Icons.bluetooth_connected)
: Icon(Icons.bluetooth_disabled),
title: Text('Device is ${snapshot.data.toString().split('.')[0]}.'),
subtitle: Text('${device.id}'),
trailing: StreamBuilder<bool>(
//The below stream is to show either a refresh button or
//CircularProgress based on the service discovering status,
//and a IndexedStack widget is used to present the needed widget
stream: device.isDiscoveringServices,
initialData: false,
builder: (c, snapshot) => IndexedStack(
index: snapshot.data ? 0 : 0,
children: <Widget>[
IconButton(
icon: Icon(Icons.refresh),
onPressed: () => device.discoverServices(),
),
IconButton(
icon: SizedBox(
child: CircularProgressIndicator(
valueColor: AlwaysStoppedAnimation(Colors.grey),
),
width: 17.0,
height: 17.0,
),
onPressed: null,
),
],
),
),
),
),
],
),
);
#override
Widget build(BuildContext context) {
return new Container(
child: Column(
children: <Widget>[
uppersection,
],
),
);
}
}

Answer 1

You should rather make upperSection a getter.
Like so:
Container get upperSection{
return Container(
child: Row(
children: <Widget>[
StreamBuilder<BluetoothDeviceState>(
stream: device.state,
initialData: BluetoothDeviceState.connecting,
builder: (c, snapshot) => ListTile(
leading: (snapshot.data == BluetoothDeviceState.connected)
? Icon(Icons.bluetooth_connected)
: Icon(Icons.bluetooth_disabled),
title: Text('Device is ${snapshot.data.toString().split('.')[0]}.'),
subtitle: Text('${device.id}'),
trailing: StreamBuilder<bool>(
//The below stream is to show either a refresh button or
//CircularProgress based on the service discovering status,
//and a IndexedStack widget is used to present the needed widget
stream: device.isDiscoveringServices,
initialData: false,
builder: (c, snapshot) => IndexedStack(
index: snapshot.data ? 0 : 0,
children: <Widget>[
IconButton(
icon: Icon(Icons.refresh),
onPressed: () => device.discoverServices(),
),
IconButton(
icon: SizedBox(
child: CircularProgressIndicator(
valueColor: AlwaysStoppedAnimation(Colors.grey),
),
width: 17.0,
height: 17.0,
),
onPressed: null,
),
],
),
),
),
),
],
),
);
}