A value of type 'bool?' can't be assigned to a variable of type 'bool' because 'bool?' is nullable and 'bool' isn't

Question

this is my complete code...

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:get/get.dart';

class DialogHelper{
  //show error dialog
 static void showErrorDialog({String title='error',String description='Something went wrong'})
  {
    Get.dialog(
      Dialog(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Text(title,style: Get.textTheme.headline4,),
              Text(description,style: Get.textTheme.headline6,),
              ElevatedButton(onPressed: () {
                if (Get.isDialogOpen) Get.back();
              },
                  child: Text('okay')),
            ],
          ),
        ),
      ),
    );

  }
}

And I got this error

19:25: Error: A value of type 'bool?' can't be assigned to a variable of type 'bool' because 'bool?' is nullable and 'bool' isn't. if (Get.isDialogOpen) Get.back();

I got error on the line if condition Get.isDialogOpen

Answer 1

You are getting that error because the getter isDialogOpen returns an Optional. This means the return value can either be a true, false or a null. But, since if-conditions can only work with Booleans, the SDK tells you there will be an error if isDialogOpen returns a null.

So to fix that, either you tell the compiler that you are sure your getter will never return a null, or you have to give a default value in case a null is returned from .isDialogOpen. We do it like this respectively;

1-

  Get.isDialogOpen! \\ this means you are sure a null can't be returned

2-

 Get.isDialogOpen ?? false \\ this means incase a null is returned use false   

Note: If you use number 1, and a null is eventually returned, your code will crash at run-time. To avoid that, you can tell the compiler to call the isDialogOpen only if it has been initialized. i.e.

Get?.isDialogOpen ?? false \\If isDialogOpen is not initialized, false will be used