How to I set up an interface listener for detecting a variable change in Kotlin. I successful implemented the following in Java, but am running into issues doing it in Kotlin:
Interface:
public interface InterfaceRefreshList
{
public void refreshListRequest();
}
Class containing listener:
public class SignalChange
{
private static boolean refreshListSwitch;
private static List<InterfaceRefreshList> refreshListListeners = new ArrayList<>();
public static void setRefreshList(boolean value)
{
refreshListSwitch = value;
for(InterfaceRefreshList l : refreshListListeners)
l.refreshListRequest();
}
public static void addRefreshListListener(InterfaceRefreshList l)
{
refreshListListeners.add(l);
}
}
Class where listener is listening:
public class FragmentBrowse extends Fragment
{
public FragmentBrowse() /// Constructor
{
SignalChange.addRefreshListListener(() -> refreshList());
}
refreshList()
{
// do something
}
}
To signal a change:
SignalChange.setRefreshList(true);
I can set up the interface and the signal class:
class SignalChange
{
private var refreshListSwitch: Boolean = false
var setSwitch: Boolean
get() = refreshListSwitch
set(value)
{
refreshListSwitch = value
}
private var refreshListListeners = ArrayList<InterfaceRefreshPersonsList>()
fun sendRefreshSignal()
{
for(l in refreshListListeners) l.refreshPersonsList()
}
fun addRefreshListListener(l: InterfaceRefreshPersonsList)
{
refreshListListeners.add(l)
}
}
But I cannot setup the listener in the FragmentBrowse class. The fragment class doesn't allow constructors.
You can use built-in Kotlin delegates, for example:
object SignalChange {
var refreshListListeners = ArrayList<InterfaceRefreshList>()
// fires off every time value of the property changes
var property1: String by Delegates.observable("initial value") { property, oldValue, newValue ->
// do your stuff here
refreshListListeners.forEach {
it.refreshListRequest()
}
}
}
interface InterfaceRefreshList {
fun refreshListRequest()
}
Add listeners like this:
SignalChange.refreshListListeners.add(object : InterfaceRefreshList {
override fun refreshListRequest() {
refreshList()
}
})
OR
Intead of interface you can use lambda:
object SignalChange {
var refreshListListeners = ArrayList<() -> Unit>()
// fires off every time value of the property changes
var property1: String by Delegates.observable("initial value") { property, oldValue, newValue ->
// do your stuff here
refreshListListeners.forEach {
it()
}
}
}
And to add listener just call:
SignalChange.refreshListListeners.add(::refreshList)
//or
SignalChange.refreshListListeners.add { refreshList() }
fun refreshList() {
}
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