Field formal parameters can only be used in a constructor. Initializing formal parameters can only be used in constructorsDRT-W1364

The analyzer produces this diagnostic when an initializing formal parameter is used in the parameter list for anything other than a constructor.

Example

The following code produces this diagnostic because the initializing formal parameter this.x is being used in the method m:

class A {
  int x = 0;

  m([this.x = 0]) {}
}

Common fixes

Replace the initializing formal parameter with a normal parameter and assign the field within the body of the method:

class A {
  int x = 0;

  m([int x = 0]) {
    this.x = x;
  }
}