kotlin - Android LiveData Observer not active after first update -

i'm trying out basic implementation of architecture component's live data kotlin this:

class marketfragment : lifecyclefragment(){ ......  override fun onactivitycreated(savedinstancestate: bundle?) {         super.onactivitycreated(savedinstancestate)         viewmodel=viewmodelproviders.of(this).get(marketviewmodel::class.java)         viewmodel.book?.observe(this, observer { book-> //updateui }) .... 

my viewmodel class created this:

class marketviewmodel : viewmodel() {     var book: mutablelivedata<book>? =mutablelivedata()     var repository: repository?= repository()      init {         update("parameter")     }      fun update(s: string)     {          book=repository?.getbook(s)      }  } 

and repository:

fun getbook(booksymbol:string):mutablelivedata<book> {     val book=mutablelivedata<book>()     ......              call . enqueue (object : callback<book> {         override fun onresponse(call: call<book>?, response: response<book>?) {              book.value=response?.body()          }      .....     })             return book } 

}

and of works great , ui updated should first time. if try make manual calls update viewmodel ui action, retrofit call still works expected new data not sent observer in fragment:

//this doesn't work: viewmodel.update("string") //this returns false: viewmodel.book.hasactiveobservers() 

is expected behaviour observer become inactive after first trigger?

you creating new mutablelivedata instance each time calling getbooks

hence observer not observing right livedata anymore.

to solve this, viewmodel should keep 1 mutablelivedata instance , post updates using postvalue function.

the repository can use rxjava (flowable) execute query on background thread , return observable<book> (or single<book>)