The parameter 'text', 'onPressed', 'outlineBtn' can't have a value of 'null' because of its type, but the implicit default value is 'null'

Issue

The code is showing the error that all of the parameters that is text, onPressed, outlineBtn can’t have the value null and this problem gets solved when I use the require keyword before them but then it starts showing this error.

Error:

Running Gradle task ‘assembleDebug’…
lib/Widget/custom_btn.dart:12:24: Warning: Operand of null-aware operation ‘??’ has type ‘bool’ which excludes null.
bool _outlineBtn = outlineBtn ?? false;
^
lib/Widget/custom_btn.dart:33:11: Warning: Operand of null-aware operation ‘??’ has type ‘String’ which excludes null.
text ?? "Text",

Here is my code:

import 'package:flutter/material.dart';

class CustomBtn extends StatelessWidget {
final String text;
final Function onPressed;
final bool outlineBtn;
CustomBtn(
  {required this.text, required this.onPressed, required this.outlineBtn});

@override
Widget build(BuildContext context) {
bool _outlineBtn = outlineBtn ?? false;

return GestureDetector(
  onTap: onPressed(),
  child: Container(
    height: 60.0,
    alignment: Alignment.center,
    decoration: BoxDecoration(
      color: _outlineBtn ? Colors.transparent : Colors.black,
      border: Border.all(
        color: Colors.black,
        width: 2.0,
      ),
      borderRadius: BorderRadius.circular(12.0),
    ),
    margin: EdgeInsets.symmetric(
      horizontal: 24.0,
      vertical: 24.0,
    ),
    child: Text(
      //Create New Account
      text ?? "Text",
      style: TextStyle(
        fontSize: 16.0,
        fontWeight: FontWeight.w600,
        color: _outlineBtn ? Colors.black : Colors.white,
      ),
    ),
  ),
);

}
}

Solution

This happens because the required keyword says that the variable must be provided and it cannot be null. In you case outlineBtn can never be null.

bool _outlineBtn = outlineBtn ?? false;

To fix this you can either omit the null check or omit the required keyword and change your variable to nullable.

final String? text;
final Function? onPressed;
final bool? outlineBtn;

Answered By – quoci

Answer Checked By – Candace Johnson (FlutterFixes Volunteer)