How to define a variable based on another variable in Flutter?-CodePudding

I am building a Flutter app with a ChangeNotifier provider. When the app is started, I make a call to the Firebase api and save the results in a Provider variable:

Map<DateTime,List> datesMap;

How can I define another variable in the same Provider, based on the first variable? for example:

List newList = datesMap[DateTime.now()]

If I try to do it I get an error:

The instance member 'params' can't be accessed in an initializer

And if I place the second variable in a Constructor, I will get an error because the first variable datesMap is null until the Firebase api is completed.

Example code:

class ShiftsProvider with ChangeNotifier {

Map<DateTime,List> datesMap;

List newList = datesMap[DateTime.now()];

Future<void> getDatesMapfromFirebase () {

some code...

datesMap = something;

notifyListeners();

return;
}

CodePudding user response：

You can use late like this:

Map<DateTime,List>? datesMap;

late List? newList = datesMap?[DateTime.now()];

CodePudding user response：

You can make getter:

List get newList {
   return datesMap[DateTime.now()];
 }

CodePudding user response：

since like I see that datesMap variable is related to the specific class, you can mark it with static keyword, this will fix your problem:

class ShiftsProvider with ChangeNotifier {

static Map<DateTime,List> datesMap;

List? newList = datesMap[DateTime.now()];

Future<void> getDatesMapfromFirebase () {

some code...

datesMap = something;

notifyListeners();

return;
}
}

just note that if you want to use that static variable, you can access it like this:

ShiftsProvider.datesMap