In Kotlin class, I have method parameter as object (See Kotlin doc here ) for class type T. As object I am passing different classes when I am calling method.
In Java we can able to compare class using instanceof of object which class it is.
So I want to check and compare at runtime which Class it is?
How can I check instanceof class in Kotlin?
Use is.
if (myInstance is String) { ... }
or the reverse !is
if (myInstance !is String) { ... }
Combining when and is:
when (x) {
is Int -> print(x + 1)
is String -> print(x.length + 1)
is IntArray -> print(x.sum())
}
copied from official documentation
We can check whether an object conforms to a given type at runtime by using the is operator or its negated form !is.
Example:
if (obj is String) {
print(obj.length)
}
if (obj !is String) {
print("Not a String")
}
Another Example in case of Custom Object:
Let, I have an obj of type CustomObject.
if (obj is CustomObject) {
print("obj is of type CustomObject")
}
if (obj !is CustomObject) {
print("obj is not of type CustomObject")
}
if, obj is automatically cast to String. So you can use properties such as length directly, without the need to explicitly cast obj to String inside the block.
You can use is:
class B
val a: A = A()
if (a is A) { /* do something */ }
when (a) {
someValue -> { /* do something */ }
is B -> { /* do something */ }
else -> { /* do something */ }
}
Try using keyword called is
Official page reference
if (obj is String) {
// obj is a String
}
if (obj !is String) {
// // obj is not a String
}
You can check like this
private var mActivity : Activity? = null
then
override fun onAttach(context: Context?) {
super.onAttach(context)
if (context is MainActivity){
mActivity = context
}
}
You can read Kotlin Documentation here https://kotlinlang.org/docs/reference/typecasts.html . We can check whether an object conforms to a given type at runtime by using the is operator or its negated form !is, for the example using is:
fun <T> getResult(args: T): Int {
if (args is String){ //check if argumen is String
return args.toString().length
}else if (args is Int){ //check if argumen is int
return args.hashCode().times(5)
}
return 0
}
then in main function i try to print and show it on terminal :
fun main() {
val stringResult = getResult("Kotlin")
val intResult = getResult(100)
// TODO 2
println(stringResult)
println(intResult)
}
This is the output
6
500
If you have a collection of objects, you can also keep those that are specific instance:
interface Fruit
class Peach: Fruit
class Watermelon: Fruit
val fruits = listOf(
Peach(),
Peach(),
Watermelon(),
Peach(),
Watermelon()
)
val peaches = fruits.filterIsInstance(Peach::class.java)
Other solution : KOTLIN
val fragment = supportFragmentManager.findFragmentById(R.id.fragment_container)
if (fragment?.tag == "MyFragment")
{}
