The constructor being called isn't a const constructor. Try removing 'const' from the constructor invocation, Flutter dart. How To Solve?

azuzu
April 26, 2024
214 views
0 votes
2 Answers

The container always displays an error like that

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        padding:  EdgeInsets.symmetric(vertical: 30),
        width: double.infinity,
        decoration: const BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.topCenter,
            colors: [
              Color.fromARGB(255, 9, 106, 185),
              Color.fromARGB(255, 56, 145, 217),
              Color.fromARGB(255, 66, 161, 239),
              Color.fromARGB(255, 109, 179, 237)
            ]
          )
        ),
        child: const Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            SizedBox(height: 80,),
            Padding(
              padding: EdgeInsets.all(20),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  Text("Login", style: TextStyle(color: Colors.white, fontSize: 40),),
                  SizedBox(height: 5,),
                  Text("Welcome Back", style: TextStyle(color: Colors.white, fontSize: 18),)
                ],
              ),      
            ),
            Expanded(
              child: Container(
              decoration:  BoxDecoration(
               color: Colors.white,
                borderRadius: BorderRadius.only(topLeft: Radius.circular(50), topRight: Radius.circular(50))
              ),
              child: Padding(
              padding: EdgeInsets.all(20),
              child: Column(
              children: <Widget>[
              Container(
                decoration: BoxDecoration(
                  boxShadow:  [BoxShadow(
                    color:  Color.fromARGB(255, 5, 97, 173),
                    blurRadius: 20,
                    offset: Offset(0,10)
                  )]
                ),
              )
            ],
          ),
        ),
      ));
          ],
        )
      ),
    );
  }
}

whereas I have deleted the const

Answers

I fixed your code, take a look

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Container(
          padding:  EdgeInsets.symmetric(vertical: 30),
          width: double.infinity,
          decoration: const BoxDecoration(
              gradient: LinearGradient(
                  begin: Alignment.topCenter,
                  colors: [
                    Color.fromARGB(255, 9, 106, 185),
                    Color.fromARGB(255, 56, 145, 217),
                    Color.fromARGB(255, 66, 161, 239),
                    Color.fromARGB(255, 109, 179, 237)
                  ]
              )
          ),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
            SizedBox(height: 80,),
          Padding(
            padding: EdgeInsets.all(20),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                Text("Login", style: TextStyle(color: Colors.white, fontSize: 40),),
                SizedBox(height: 5,),
                Text("Welcome Back", style: TextStyle(color: Colors.white, fontSize: 18),)
              ],
            ),
          ),
          Expanded(
              child: Container(
                decoration:  BoxDecoration(
                    color: Colors.white,
                    borderRadius: BorderRadius.only(topLeft: Radius.circular(50), topRight: Radius.circular(50))
                ),
                child: Padding(
                  padding: EdgeInsets.all(20),
                  child: Column(
                    children: <Widget>[
                      Container(
                        decoration: BoxDecoration(
                            boxShadow:  [BoxShadow(
                                color:  Color.fromARGB(255, 5, 97, 173),
                                blurRadius: 20,
                                offset: Offset(0,10)
                            )]
                        ),
                      )
                    ],
                  ),
                ),
              )
          )
          ],
        )
    ),
    );
  }
}

for more Flutter Constant constructors information, please check link.

Working code:

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
          padding: const EdgeInsets.symmetric(vertical: 30),
          width: double.infinity,
          decoration: const BoxDecoration(
              gradient: LinearGradient(begin: Alignment.topCenter, colors: [
            Color.fromARGB(255, 9, 106, 185),
            Color.fromARGB(255, 56, 145, 217),
            Color.fromARGB(255, 66, 161, 239),
            Color.fromARGB(255, 109, 179, 237)
          ])),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              const SizedBox(
                height: 80,
              ),
              const Padding(
                padding: EdgeInsets.all(20),
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: <Widget>[
                    Text(
                      "Login",
                      style: TextStyle(color: Colors.white, fontSize: 40),
                    ),
                    SizedBox(
                      height: 5,
                    ),
                    Text(
                      "Welcome Back",
                      style: TextStyle(color: Colors.white, fontSize: 18),
                    )
                  ],
                ),
              ),
              Expanded(
                  child: Container(
                decoration: const BoxDecoration(
                    color: Colors.white,
                    borderRadius: BorderRadius.only(
                        topLeft: Radius.circular(50),
                        topRight: Radius.circular(50))),
                child: Padding(
                  padding: const EdgeInsets.all(20),
                  child: Column(
                    children: <Widget>[
                      Container(
                        decoration: const BoxDecoration(boxShadow: [
                          BoxShadow(
                              color: Color.fromARGB(255, 5, 97, 173),
                              blurRadius: 20,
                              offset: Offset(0, 10))
                        ]),
                      )
                    ],
                  ),
                ),
              )),
            ],
          )),
    );
  }
}

What I did is: Removed const in front of Column widget and added const on children’s of Column as per the lint.

Explanation: We can’t make constant Container widget due to that you are getting. If you see the Container widget, we do not have a constant constructor, due to which we are unable to use const keyword in Container widget.

I hope this is helpful. Thank you.

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