The argument type 'void Function(int)' can't be assigned to the parameter type 'void Function(int?)?' [closed]

Question

Hello for all I have problem so I want to best solution for this code enter image description here

It shows The argument type

'void Function(int)' can't be assigned to the parameter type 'void Function(int?)?'.

Answer 1

Update:

(int newColor) {...}

to

(int? newColor) {...}

Answer 2

This is null safety error

define color variable like this:

int? color;

also change the following lines to this:

int? newColor;
saveColor(newColor!);

for more info about null safety: https://dart.dev/null-safety