RxJava - 如何在发出新项目时停止正在运行的任务

Question

I am building searching feature for my Android app with RxJava. When users type/change query characters in an EditText , an emitter will emit new query text and I search around my database to get results that match the query.

getEditTextObservable()
                .subscribeOn(Schedulers.computation())
                .debounce(500, TimeUnit.MILLISECONDS)
                .filter {
                    !it.isNullOrEmpty()
                }
                .map {
                    //start searching
                    getResultsInDatabase(it) //this function takes a long time to complete
                }.observeOn(AndroidSchedulers.mainThread())
                .subscribe{
                    //render results on screen
                }

The method getResultsInDatabase(string:String) take a long time to complete, when the query text changed, I want to stop method getResultsInDatabase(string:String) (in case it is running with previously emitted query) to run it again with new query. How can I do to achieve that? I would appreciate your helps. Thank you for reading my question.

Answer 1

You need a switchMap .

getEditTextObservable()
    .subscribeOn(Schedulers.computation())
    .debounce(500, TimeUnit.MILLISECONDS)
    .filter { !it.isNullOrEmpty() } //Be careful with this. Should clearing text clear results too?
    .switchMap { 
        Observable.fromCallable { getResultsInDatabase(it) }.subscribeOn(Schedulers.io()) 
    }.observeOn(AndroidSchedulers.mainThread())
    .subscribe{
        //render results on screen
    }

Answer 2

You can use valve to pause a stream in RxJava . Based on the value of it, the stream continues to emit or will be kept in a paused state.