Flutter the instance member can’t be accessed in an initializer

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Flutter: The Instance Member Can’t be Accessed in an Initializer

When working with Flutter, you may encounter the error message “The instance member can’t be accessed in an initializer” when trying to access an instance variable within the initializer of a class. This error occurs because instance variables can only be accessed after the initialization phase is complete.

To understand this error better, let’s take a look at an example: 


class Foo {
  int x;

  Foo(int y) {
    x = y;
  }
}

void main() {
  Foo foo = Foo(5);
  print(foo.x);
}

In the example above, we have a class named “Foo” with an instance variable “x”. In the constructor of “Foo”, we try to assign the value of the parameter “y” to “x”. However, this results in the mentioned error.

To fix this error, we have a couple of options. One option is to use a constructor with named parameters, and initialize the instance variable in the body of the constructor: 


class Foo {
  int x;

  Foo({required int y}) {
    x = y;
  }
}

void main() {
  Foo foo = Foo(y: 5);
  print(foo.x);
}

In the updated example, we defined a named parameter “y” for the constructor of “Foo”. This allows us to pass the value of “y” using named arguments while creating an instance of “Foo”. Then, within the body of the constructor, we assign the value of “y” to “x”. This approach ensures that the initialization phase is complete before accessing the instance variable.

Another option is to use a constructor initializer list to directly assign the value of the parameter to the instance variable: 


class Foo {
  int x;

  Foo(int y) : x = y;
}

void main() {
  Foo foo = Foo(5);
  print(foo.x);
}

In this updated example, we use a constructor initializer list to set the value of “x” directly to the value of “y”. This also ensures that the instance variable is correctly initialized before it is accessed.

By using one of these approaches, you can overcome the “The instance member can’t be accessed in an initializer” error in Flutter.

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