lateinit modifier is not allowed on primitive type

问题:

I am defining like a instance variable in kotlin and want to initialize it onCreate method of an activity.

var count: Int
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    count.inc()
}

Here I am getting a below error on count variable.

Property must be initialized or be abstract in Kotlin

Well, I read this thread Property must be initialized or be abstract and tried same but again I am getting a below error.

lateinit modifier is not allowed on primitive type properties

lateinit var count: Int
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    count.inc()
}

Is there any way to do this in Kotlin ?

回答1:

There are several ways to resolve this issue.

You can Initialise it with default value (e.i 0 or -1 or whatever) and then initialise it whenever your logic says.

Or tell compiler that count will be initialised later in this code by using Delegates.notNull check notNull.

var count: Int by Delegates.notNull<Int>()

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    // You can not call `Int.inc()` in onCreate()` function until `count` is initialised.
    // count.inc()
    // **initialise count** 
}

And if you need count value on demand (if not necessary to initialise in onCreate), you can use lazy function. Use this only if you have an intensive (Some calculation/Inflating a layout etc) task that you want to do on demand, Not to just assign a value.

var count:Int by lazy {
    // initialise
}

Now you can decide what to use.

I hope it helps.

回答2:

There's no reason to leave it uninitialized. Just initialize it to 0 or -1.

lateinit is for non-null object references that can't easily be initialized in the class body definition.