Will the same value trigger the event in LiveDate? - kotlin

Question

The Code A and Image A is from the artical LiveData with SnackBar, Navigation and other events (the SingleLiveEvent case).
The author told me "Trigger the event by setting a new Event as a new value", I think it should be "Trigger the event by setting a new Event as any value", right?
For example,
Step 1: The user clicks the button in master Activity with the code userClicksOnButton("StartDetails") , the Details Activity will start.
Step 2: The user presses back, coming back to the master activity
Step 3: The user clicks the button in master Activity with the code userClicksOnButton("StartDetails") again, the Details Activity will start again.
Is it right?
Code A
class ListViewModel : ViewModel {
private val _navigateToDetails = MutableLiveData<Event<String>>()
val navigateToDetails : LiveData<Event<String>>
get() = _navigateToDetails
fun userClicksOnButton(itemId: String) {
_navigateToDetails.value = Event(itemId) // Trigger the event by setting a new Event as a new value
}
}
open class Event<out T>(private val content: T) {
var hasBeenHandled = false
private set // Allow external read but not write
/**
* Returns the content and prevents its use again.
*/
fun getContentIfNotHandled(): T? {
return if (hasBeenHandled) {
null
} else {
hasBeenHandled = true
content
}
}
/**
* Returns the content, even if it's already been handled.
*/
fun peekContent(): T = content
}
myViewModel.navigateToDetails.observe(this, Observer {
it.getContentIfNotHandled()?.let { // Only proceed if the event has never been handled
startActivity(DetailsActivity...)
}
})
Image A

Answer 1

You're having two different constraints on the data.
The LiveData emits every update to active observers, but the event itself is stateful. Thus a new event is required as a new LiveData value. The itemId could be any value, but the comment doesn't refer to it.
Trigger the event by setting a new Event as [a new] value