Android Development with Kotlin

Safe call

The safe call operator is simply a question mark followed by a dot. It's important to understand that the safe cast operator will always return a value. If the left-hand side of the operator is null, then it will return null, otherwise it will return the result of the right-hand side expression:

    override fun onCreate(savedInstanceState: Bundle?) { 
         super.onCreate(savedInstanceState) 
         val locked: Boolean? = savedInstanceState?.getBoolean("locked") 
    } 

If savedInstanceState is null, then null will be returned, otherwise the result of evaluating a savedInstanceState?.getBoolean("locked") expression will be returned. Keep in mind that a nullable reference call always returns nullable, so the result of the whole expression is a nullable ...