falconGitHub

prefer-align-over-container

Group
Style
Path
lint/style/prefer-align-over-container
Default
Off, opt in
Origin
Falcon
Domain
flutter
Rule
313 of 512
flutter

Prefers Align over a Container used only for alignment.

The unnamed Flutter constructor must have a provably non-null child and a provably non-null alignment argument, with only an optional key. Other arguments, nullable or unresolved values, and shadowed constructors are ignored. The dedicated widget makes the layout intent explicit. Contexts explicitly requiring Container are excluded.

Invalid

example.dartdart
import 'package:flutter/material.dart';
import 'package:flutter/material.dart' as ui;

typedef LayoutContainer = Container;

void examples(Widget child, AlignmentGeometry value) {
  Container(alignment: value, child: child);
  new Container(alignment: value, child: child);
  ui.Container(child: child, alignment: value);
  new ui.Container(key: const Key("box"), alignment: value, child: child);
  LayoutContainer(alignment: value, child: child);
  Container(key: const Key("ordered"), child: child, alignment: (value));
}
Prefer `Align` over a `Container` used only for alignment.
6void examples(Widget child, AlignmentGeometry value) {
7 Container(alignment: value, child: child);
Prefer `Align` over a `Container` used only for alignment.
7 Container(alignment: value, child: child);
8 new Container(alignment: value, child: child);
Prefer `Align` over a `Container` used only for alignment.
8 new Container(alignment: value, child: child);
9 ui.Container(child: child, alignment: value);
Prefer `Align` over a `Container` used only for alignment.
9 ui.Container(child: child, alignment: value);
10 new ui.Container(key: const Key("box"), alignment: value, child: child);
Prefer `Align` over a `Container` used only for alignment.
10 new ui.Container(key: const Key("box"), alignment: value, child: child);
11 LayoutContainer(alignment: value, child: child);
Prefer `Align` over a `Container` used only for alignment.
11 LayoutContainer(alignment: value, child: child);
12 Container(key: const Key("ordered"), child: child, alignment: (value));

Valid

example.dartdart
import 'package:flutter/material.dart';
import 'package:flutter/material.dart' as ui;

typedef LayoutContainer = Container;

void keepContainer(Widget child, AlignmentGeometry value, AlignmentGeometry? nullable, Widget? nullableChild, dynamic unknown) {
  Container(alignment: value);
  Container(child: child);
  Container(alignment: null, child: child);
  Container(alignment: nullable, child: child);
  Container(alignment: unknown, child: child);
  Container(alignment: value, child: null);
  Container(alignment: value, child: nullableChild);
  Container(alignment: value, width: 12, child: child);
  Container(alignment: value, decoration: const BoxDecoration(), child: child);
  Container(alignment: value, color: Colors.red, child: child);
}

Object parameterShadow(dynamic Container, Widget child, AlignmentGeometry value) =>
    Container(alignment: value, child: child);

Object prefixShadow(dynamic ui, Widget child, AlignmentGeometry value) =>
    ui.Container(alignment: value, child: child);

Object aliasShadow(dynamic LayoutContainer, Widget child, AlignmentGeometry value) =>
    LayoutContainer(alignment: value, child: child);

void localShadow(dynamic factory, Widget child, AlignmentGeometry value) {
  final Container = factory;
  Container(alignment: value, child: child);
}

void unusedTransformAlignment(Widget child, AlignmentGeometry value) {
  Container(alignment: value, transformAlignment: Alignment.center, child: child);
}

Configure prefer-align-over-container

Set its severity in falcon.json. See the configuration guide.

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-align-over-container": "error"
      }
    }
  }
}

Or silence one occurrence with a suppression comment; the reason is required.

example.dartdart
// falcon-ignore lint/style/prefer-align-over-container: <reason>