Expecting Member Declaration in Kotlin
I Want to Assign My Class Variable in Constructor, but I Get an Error 'Expecting Member Declaration' Class Ylaservice { Var Context: Context? =Null Class...
I want to assign my class variable in constructor, but I get an error 'expecting member declaration'
class YLAService {
var context:Context?=null
class YLAService constructor(context: Context) {
this.context=context;// do something
}
}
2 Answers
In Kotlin you can use constructors like so:
class YLAService constructor(val context: Context) {
}
Even shorter:
class YLAService(val context: Context) {
}
If you want to do some processing first:
class YLAService(context: Context) {
val locationService: LocationManager
init {
locationService = context.getService(LocationManager::class.java)
}
}
If you really want to use a secondary constructor:
class YLAService {
val context: Context
constructor(context: Context) {
this.context = context
}
}
This looks more like the Java variant, but is more verbose.
See the Kotlin reference on constructors.
I'll just add some info and give real example. When you want to initialize class && trigger some event, like some method, in Python we can simply call self.some_func() being in __init__ or even outside. In Kotlin we're restricted from calling simple in the context of the class, i.e.:
class SomeClass {
this.cannotCallFunctionFromHere()
}
For such purposes I use init. It's different from constructor in a way that we don't clutter class schema && allows to make some processing.
Example where we call this.traverseNodes before any further actions are done with the methods, i.e. it's done during class initialization:
class BSTIterator(root: TreeNode?) {
private var nodes = mutableListOf<Int>()
private var idx: Int = 0
init {
this.traverseNodes(root)
}
fun next(): Int {
val return_node = this.nodes[this.idx]
this.idx += 1
return return_node
}
fun hasNext(): Boolean {
when {
this.idx < this.nodes.size -> {
return true
} else -> {
return false
}
}
}
fun traverseNodes(node: TreeNode?) {
if(node!!.left != null) {
this.traverseNodes(node.left)
}
this.nodes.add(node.`val`)
if(node!!.right != null) {
this.traverseNodes(node.right)
}
}
}
Hope it also helps someone
James Sterling reports on renewable energy developments, climate policy, ecological conservation, and green tech innovations around the globe.
