Kotlin: Init function and variable initialization

Question

I'm building a component for my app and I started to use init function instead of constructor more often, but now weird thing is happening. If I call function inside init function to initialize list, it throws NullPointerException on that list. Is init function executed before variables are initialized in particular class?

Exception is thrown in removeAllViews.

Code:

init {
        createViews()
    }

    private var viewList = mutableListOf<ViewGroup>()
    private fun createViews(){
        removeAllViews()
        list.forEach { addItem(it) }
        changeViewsState(true)
    }

    private fun removeAllViews(){
        parent.removeAllViews()
        viewList.clear()
    }

Does this answer your question? init block position in class in Kotlin — JensV
– JensV, Commented Apr 13, 2021 at 9:17

Simone · Accepted Answer · 2021-04-13 09:20:50Z

6

From this section fo the offcial documentation: https://kotlinlang.org/docs/classes.html#constructors

During an instance initialization, the initializer blocks are executed in the same order as they appear in the class body, interleaved with the property initializers.

So you should put the variable declaration before the init:

private var viewList = mutableListOf<ViewGroup>()

init {
    createViews()
}
private fun createViews(){
    removeAllViews()
    list.forEach { addItem(it) }
    changeViewsState(true)
}

private fun removeAllViews(){
    parent.removeAllViews()
    viewList.clear()
}

answered Apr 13, 2021 at 9:20

Simone

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