limit number of selected checkboxes

Issue

i have multiple checkboxes .. in which you can select more than one checkbox ... like this:

for (var a in user.poll.questions[i].options) {
          children.add(
            new Row(
              children: [
                new Checkbox(
                    value: questionList.contains(a.id),
                    onChanged: (bool newValue) {
                      setState(() {
                        //if (questionList.length < user.poll.questions[i].maxChoice){
                        newValue
                            ? questionList.add(a.id)
                            : questionList.remove(a.id);
                        //}
                      });
                      answers[user.poll.questions[i].id] = questionList;
                    }),
                new Text(
                  a.text,
                  style: TextStyle(fontSize: 16.0),
                ),
              ],
            ),
          );
        }

but i want to limit number of checked boxes .. am getting the max choices number from json .. how to limit the selection of checkedboxes by it?

for example if

int maxChoices = 3;

how can i let the user selects maximum of 3 checkboxes?

Solution

Don't you want to do something like this?

(newValue && questionList.length >= maxChoices)
    ? showAlert() : setState(() {
        newValue
            ? questionList.add(a.id)
            : questionList.remove(a.id);
         });

Answered By - Andrey Turkovsky