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【Flutter/Dart】Cannot provide both a color and a decoration のエラーの解決策

Last updated at Posted at 2021-12-08

環境

-> %  sw_vers
ProductName:    macOS
ProductVersion: 12.0.1
BuildVersion:   21A559

-> % flutter --version
Flutter 2.5.3  channel stable  https://github.com/flutter/flutter.git
Tools  Dart 2.14.4

実装したかったこと

スクリーンショット 2021-12-08 21.57.06.png

このような角丸で背景色のあるWidgetを作成したい🔵

エラー文

════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown building Practice(dirty):
Cannot provide both a color and a decoration
To provide both, use "decoration: BoxDecoration(color: color)".
'package:flutter/src/widgets/container.dart':
package:flutter//widgets/container.dart:1
Failed assertion: line 274 pos 15: 'color == null || decoration == null'

エラーが発生した際のコード

class Practice extends StatelessWidget {
  const Practice12({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: 
          Container(
            color: Colors.blue,
            width: 100,
            height: 100,
            decoration: BoxDecoration(borderRadius: BorderRadius.circular(16)),
          ),
    );
  }
}

修正したコード

To provide both, use "decoration: BoxDecoration(color: color)". 'package:flutter/src/widgets/container.dart':

ということで、答えはエラー文に書いてありました☺️

ContainerクラスのcolorプロパティとBoxDecorationを併用するのはうまくいかなそうなので、
代わりにBoxDecorationクラスのcolorプロパティを使用するように変更することで意図したWidgetが実装できました!


class Practice extends StatelessWidget {
  const Practice({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child:  Container(
            width: 100,
            height: 100,
            decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(16), color: Colors.blue),
          ),
    );
  }
}

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