title: Invalid constant value.dart(invalid_constant)
body: <p>in the bellow code I got the error on &quot; controller: urlController,&quot; this line</p>
  <pre><code>      var url;
        final urlController = TextEditingController();
      
        @override
        void dispose() {
          urlController.dispose();
          super.dispose();
        }
      
        @override
        Widget build(BuildContext context) {
          return Scaffold(
            appBar: AppBar(
              backgroundColor: const Color(0xff16352A),
              title: const Text(
                'Downloader',
                style: TextStyle(color: Color(0xffEDAB24)),
              ),
            ),
            body: Container(
              padding: const EdgeInsets.all(20.0),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: [
                  const SizedBox(height: 50.0),
                  const TextField(
                    controller: urlController,
                    decoration: InputDecoration(
                      border: OutlineInputBorder(),
                      labelText: 'Paste URL',
                    ),
                  ),
              
  
  const SizedBox(height: 20.0),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                children: [
                  TextButton(
                    onPressed: () {},
                    child: const Text(
                      'Download',
                      style: TextStyle(fontSize: 30.0),
                    ),
                    style: TextButton.styleFrom(
                      primary: Colors.white,
                      backgroundColor: const Color(0xff284635),
                    ),
                  ),
                  const SizedBox(width: 20.0),
                  TextButton(
                    onPressed: () {
                      setState(() {
                        url = urlController.text;
                      });
                    },
                    child: const Text(
                      'Clear',
                      style: TextStyle(fontSize: 30.0),
                    ),
                    style: TextButton.styleFrom(
                      primary: Colors.white,
                      backgroundColor: const Color(0xff284635),
                    ),
                  ),
                ],
              )
            ],
          ),
        ),
      );
    }
  }
  </code></pre>