undefined_extension_getter

The getter '{0}' isn't defined for the extension '{1}'.

The analyzer produces this diagnostic when an extension override is used to invoke a getter, but the getter isn't defined by the specified extension. The analyzer also produces this diagnostic when a static getter is referenced but isn't defined by the specified extension.

The following code produces this diagnostic because the extension E doesn't declare an instance getter named b:

extension E on String {
  String get a => 'a';
}

extension F on String {
  String get b => 'b';
}

void f() {
  E('c').b;
}

The following code produces this diagnostic because the extension E doesn't declare a static getter named a:

extension E on String {}

var x = E.a;

If the name of the getter is incorrect, then change it to the name of an existing getter:

extension E on String {
  String get a => 'a';
}

extension F on String {
  String get b => 'b';
}

void f() {
  E('c').a;
}

If the name of the getter is correct but the name of the extension is wrong, then change the name of the extension to the correct name:

extension E on String {
  String get a => 'a';
}

extension F on String {
  String get b => 'b';
}

void f() {
  F('c').b;
}

If the name of the getter and extension are both correct, but the getter isn't defined, then define the getter:

extension E on String {
  String get a => 'a';
  String get b => 'z';
}

extension F on String {
  String get b => 'b';
}

void f() {
  E('c').b;
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.