How to Store Class in a Variable Kotlin

Question

i want to store a Class in a variable, the purpose is to check if other variable is an instanceOf the class
Here is My Code :

            when (it.itemId) {
                R.id.vend_list -> {
                    replace(R.id.fragmentContainer, vendingList)
                    id = VendListClass
                }
                R.id.label -> {
                    replace(R.id.fragmentContainer, label)
                    id = LabelClass
                }
                R.id.home -> {
                    replace(R.id.fragmentContainer, mainMenu)
                    id = MainMenuClass
                }
                R.id.statistic -> {
                    replace(R.id.fragmentContainer, statistic)
                    id = StatisticClass
                }
                else -> {}
            }

            for(fragment in supportFragmentManager.fragments){
                if(fragment !is id){
                    remove(fragment)
                }
            }

Kent · Accepted Answer · 2021-12-17 23:56:47Z

4

I don't know your exact requirement. But it probably could be designed in other ways, enum? sealed classes? inheritances?

Anyway, straight to your question, hope this helps:

val listCls = List::class
val strCls = String::class

val listObj = listOf(1,2,3)

println("check listObj and listCls: ${listCls.isInstance(listObj)}")
println("check listObj and strCls: ${strCls.isInstance(listObj)}")

output:

check listObj and listCls: true
check listObj and strCls: false

answered Dec 17, 2021 at 23:56

Kent

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2 Comments

Jooo21 Over a year ago

what is the type of listCls and strCls? I need to store a different Class in one variable using when() conditions. and then i will check if other object is an instance of that Class

Kent Over a year ago

@Jooo21 the two *Cls variable is with type KClass you can of course use one variable.

Ma3x · Accepted Answer · 2021-12-18 21:06:49Z

You can store a class reference in a KClass<*> variable using ::class or in a Class<*> variable using ::class.java

So based on your original code, this is how you could do it

            // this has to be a nullable type because of your else option
            var id: KClass<*>? = null
    
            when (it.itemId) {
                R.id.vend_list -> {
                    replace(R.id.fragmentContainer, vendingList)
                    id = VendListClass::class
                }
                R.id.label -> {
                    replace(R.id.fragmentContainer, label)
                    id = LabelClass::class
                }
                R.id.home -> {
                    replace(R.id.fragmentContainer, mainMenu)
                    id = MainMenuClass::class
                }
                R.id.statistic -> {
                    replace(R.id.fragmentContainer, statistic)
                    id = StatisticClass::class
                }
                else -> {}
            }

            for(fragment in supportFragmentManager.fragments){
                // if the else option from when has to remove all
                // fragments, just flip the condition to
                // if(id == null || id.isInstance(fragment))
                if(id != null && id.isInstance(fragment)){
                    remove(fragment)
                }
            }

This was my breakthrough: myClass.isInstance(obj). Thanks!

Brian Tompsett - 汤莱恩 · Accepted Answer · 2021-12-19 16:56:51Z

0

Thanks @Kent for helping, but I figured out how to solve this in an ineffective way.

Here is my code:

val obj1 = Object1()
val obj2 = Object2()
val obj3 = Object3()
val obj4 = Object4()

var id : SuperObject? = null

when(certainConditions) {
   option1 -> id = Object1()
   option2 -> id = Object2()
   option3 -> id = Object3()
   option4 -> id = Object4()
}

val otherObject = Object1()

if(id == otherObject) {
    //process logic
}

I'm still looking for the more effective way though.
If anyone found out a better way, please share your answer.

edited Dec 19, 2021 at 16:56

Brian Tompsett - 汤莱恩

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answered Dec 18, 2021 at 20:40

Jooo21

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1 Comment

al3c Over a year ago

it's called an enum

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