How to negate a boolean expression when using the elvis operator in kotlin?

Question

I want to negate the following expression:

return SpUtils.loadEMail()?.isEmpty() ?: false

If i add a ! before the expression, like

return !SpUtils.loadEMail()?.isEmpty() ?: false

The IDE(Android Studio) tells me

Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type kotlin.Boolean?

How do I negate this kinds of expressions?

Answer 1

You have problem with nullable reference.

 SpUtils.loadEMail()?.isEmpty()

This code produces value of type Boolean? that's mean expression can return an instance of Boolean or null.

I suggest following code to solve your problem:

return !(SpUtils().loadEMail()?.isEmpty() ?: false);

You trying negate Boolean? instead of Boolean, that elvis operator returns!