How can I make a variable in the constructor make it optional (flutter)?-CodePudding

please help me solve the following problem. This part of my code:

class MeditationCard extends StatelessWidget {
  const MeditationCard({
    required this.title,
    required this.image,
    this.route});

final String title;
final String image;
final String route;
...

I need the route variable as optional, but when I remove the flag, I get an error and ask me to make the variable mandatory. Tried different approaches but didn't work for me This alert dialog

The parameter 'route' can't have a value of 'null' because of its type, but the implicit default value is 'null'.

CodePudding user response：

This happened because of null safety check.In order to set nullable variable, you should use ?, try this:

final String? route;

CodePudding user response：

You can make it nullable (?) or define default value

Example for nullable

class MeditationCard extends StatelessWidget {
  const MeditationCard({
    required this.title,
    required this.image,
    this.route});

final String title;
final String image;
final String? route;

CodePudding user response：

I know you got the proper answer to your question. But I wanted to mention another method to solve this issue that might help you in the future, which is to provide a default value. This way you avoid weird null errors and null checking.

class MeditationCard extends StatelessWidget {
  const MeditationCard({
    required this.title,
    required this.image,
    required this.route});

final String title;
final String image;
final String route = 'default route';
}

This way you ensure that the property 'route' has a value and is never null. And you can override it when you need to.