CODEWITHSUNDEEP
kotlincompanion-object
alessandro gaboardi
alessandro gaboardi

Reputation: 959

Access methods outside companion object - Kotlin

I'm pretty new to kotlin and I was wondering if it's possible, and if it's against best practice to access methods and variables that are outside a companion object, from within the companion object.

For example

class A {
    fun doStuff(): Boolean = return true

    companion object{
        public fun stuffDone(): Boolean = return doStuff()
    }
}

or something like that

Thank you

Upvotes: 21

Views: 27553

Answers (3)

Erick Cabral
Erick Cabral

Reputation: 170

A correct way to do what you want is:

  1. create a instance of your main class inside Companion Objects
  2. initialize the instance when you instance the Main Class
  3. call the instance of the class when you need to call methods, set or get variables.

For a better control and better decouple level, you should access/set/get stuff from the main class (A) from the Companion Object instead of calling getInstance() to access the Main Class stuff.

Example:

 class A {
        
        private val myPrivateVariable:String = "MY_STUFF"
       
        init{
            setupInstance(this@A)
        }
        
        companion object{
           private val instance:A? = null
           
           fun setupInstance(a:A){
               this.instance = a
           }
           
           //IF YOU WANT TO ACCESS CLASS A METHODS/VARIABLES DIRECTLY YOU CAN CALL IT
           fun getInstance():A{
               return this.instance?.let{
                   it
                   }?:throw NullPointerException("INSTANCE NOT SET YET")
           }
           
           //ACCESSING CLASS A VARIABLES FROM COMPANION OBJECT (BETTER ERROR CONTROL AND DECOUPLED)
           fun setMyVariable(string:String){
               this.getInstance().myPrivateVariable = string
           }
            
            fun getMyVariable(string:String) = this.getInstance().myPrivateVariable    
          
        }
    }

Upvotes: 0

Uddhav P. Gautam
Uddhav P. Gautam

Reputation: 7626

You can also call functions that are outside of companion object block.

class A {
    fun doStuff() = true

    companion object {
        val a = A()
        fun stuffDone() = a.doStuff() 
    }
}

Upvotes: 3

yole
yole

Reputation: 97148

doStuff() is an instance method of a class; calling it requires a class instance. Members of a companion object, just like static methods in Java, do not have a class instance in scope. Therefore, to call an instance method from a companion object method, you need to provide an instance explicitly:

class A {
    fun doStuff() = true

    companion object {
        fun stuffDone(a: A) = a.doStuff() 
    }
}

Upvotes: 40

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