[Flutter/Dart] Countermeasure when you want to perform asynchronous process in the constructor

Problem

There are times when you want to do asynchronous process in the constructor of a Dart class.

For example, the initial value is the value obtained from the remote database.

However, the syntax below will result in a compilation error.

class testClass{

  testClass()async{  
    await _init();
  }
//← The modifier 'async' can't be applied to the body of a constructor.

  Future<void> _init()async{
    await Future.delayed(const Duration(seconds: 1));
  }
}

It seems that the constructor should return a testClass, not a Future.

However the following compiles, but parent process does not wait for _init() to complete.

class testClass{

  testClass(){  
　　　_init();
  }

  Future<void> _init()async{
    await Future.delayed(const Duration(seconds: 1));
  }
}

That is,

class testClass{

  testClass(){  
　　　_init();
    debugPrint("construct");
  }

  Future<void> _init()async{
    await Future.delayed(const Duration(seconds: 1));
    debugPrint("init");
  }
}

void main(){

  testClass _test = testClass();
  debugPrint("done");
}

results in

flutter: construct
flutter: done
flutter: init

Countermeasure

Create a static method that creates an instance.

class testClass{

  testClass(){

  }

  static Future<testClass> create()async{
    testClass _test = testClass();
    await _test._init();
    debugPrint("construct");
    return _test;
  }

  Future<void> _init()async{
    await Future.delayed(const Duration(seconds: 1));
    debugPrint("init");
  }
}

If you do the following

void main()async{

    testClass _test = await testClass.create();
    debugPrint("done");
}

flutter: init
flutter: construct
flutter: done

the order went as expected.

Lastly

There seems to be a lot of controversy regarding this topic, such as wanting to be able to use constructors instead of static methods, or that constructors shouldn't be awaited in the first place.

Reference

Allow async constructors (or at least factory constructors)

Calling an async method from a constructor in Dart