Use of Boolean? in if expression

Question

If I have a nullable Boolean b, I can do the following comparison in Java:

Boolean b = ...;
if (b != null && b) {
   /* Do something */
         


        

Answer 1

From what I've seen the Boolean? is a result of a method that returns Boolean on an object that is nullable

val person: Person? = null
....
if(person?.isHome()) { //This won't compile because the result is Boolean?
  //Do something
}

The solution I've been using is to use the let function to remove the possible returned null value like so

person?.let {
  if(it.isHome()) {
    //Do something
  }
}

Answer 2

For Kotlin what i normally use is

if (object?.booleanProperty ==true)
   { 
     //do stuff 
   }

this would only work when the property is true and the object is not null. For the reverse:

if (!object?booleanProperty !=true)
   { 
     //do Stuff
   }

Answer 3

Let's use an if-else statement with an Elvis Operator:

val a: Boolean?
val b: Boolean?

a = true
b = null

if (a != null ?: b) { 
    println("One of them isn't nullable...")
} else {
    println("Both are nullables!")
}

// Result: "One of them isn't nullable..."

a = null
b = null

if (a != null ?: b) { 
    println("One of them isn't nullable...")
} else {
    println("Both are nullables!")
}

// Result: "Both are nullables!"

Answer 4

It's pretty easy to add an extension function if that helps you.

fun Boolean?.orDefault(default: Boolean = false): Boolean {
    if (this == null)
        return default
    return this
}

var x: Boolean? = null

if(x.orDefault()) {
..
}

Answer 5

first, add the custom inline function below:

inline fun Boolean?.ifTrue(block: Boolean.() -> Unit): Boolean? {
    if (this == true) {
        block()
    }
    return this
}

inline fun Boolean?.ifFalse(block: Boolean?.() -> Unit): Boolean? {
    if (null == this || !this) {
        block()
    }

    return this
}

then you can write code like this:

val b: Boolean? = ...
b.ifTrue {
   /* Do something in true case */
}

//or

b.ifFalse {
   /* Do something else in false case */
}