RxJava

A RxJava Basics

Creating observables

create() - Observable.create()
just() -  Observable.just("first", "second", "third", "fourth", "fifth", "sixth",
          "seventh", "eighth", "ninth", "tenth")
          .subscribeOn(Schedulers.io()) // What thread to do the work on
          .observeOn(AndroidSchedulers.mainThread())
range() - Observable.range(0,11)
repeat() - Observable.range(0,3)
        .repeat(2)
// converts an array of objects into observables
// Task[] list = new Task[5];
fromArray() - Observable
        .fromArray(list) 
// converts an array of iterables like  List, ArrayList, Set into obserbvables
// List<Task> taskList = new ArrayList<>();
fromIterable() - Observable
        .fromIterable(taskList)
// fromCallable() will execute a block of code (usually a method) and return a result. 
//You need to return a Task object from a local SQLite database cache. 
//All database operations must be done on a background thread. 
//Then the result is returned to the main thread.

fromCallable() - Observable
        .fromCallable(new Callable<Task>() {
            @Override
            public Task call() throws Exception {
                return MyDatabase.getTask();
            }
        })

example codes

    fun loadUserData() {
        val userPosts = getUserData()
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe {
                    setUserData(it)
                }
    }

    /**
     * get user data with posts using flatmap operator
     */
    private fun getUserWithPosts(): Observable<UserWithPosts> {

        return userRepository.getUserDetailObservable(uid).flatMap { user ->
            val userWithPosts = UserWithPosts(user, arrayListOf())

            userRepository.getAllUserPosts(uid, 1).map {
                val userPostList = mutableListOf<UserPosts>()
                userPostList.add(UserPosts("Posts", "Post is empty", UserPostsActivity.POST, it))
                userWithPosts.userPosts = userPostList
                        userWithPosts
            }
        }.flatMap { userWithPosts ->
            userRepository.getUserRecommededPosts(uid, 1).map {
                val userPostList = mutableListOf<UserPosts>()
                userPostList.add(UserPosts("Recommendation", "Recommendation is empty", UserPostsActivity.RECOMMEDATION, it))
                userWithPosts.userPosts = userPostList
                 userWithPosts
            }

        }.flatMap { userWithPosts ->
            userRepository.getUserWishList(uid, 1).map {
                val userPostList = mutableListOf<UserPosts>()
                userPostList.add(UserPosts("WishList", "Wishlist is empty", UserPostsActivity.WISHLIST, it))
                userWithPosts.userPosts = userPostList
                userWithPosts
            }

        }
    }

    /**
     * get user data with posts using zip operator
     */
    private fun getUserData(): Observable<UserWithPosts> {

        return Observable.zip(userRepository.getUserDetailObservable(uid),
                userRepository.getAllUserPosts(uid, 1),
                userRepository.getUserRecommededPosts(uid, 1),
                userRepository.getUserWishList(uid, 1),
                Function4<User, List<Post>, List<Post>, List<Post>, UserWithPosts>
                { user, allposts, recommendedposts, wishlistposts ->
                    val userPostList = mutableListOf<UserPosts>()
                    userPostList.add(UserPosts("Posts", "Post is empty", UserPostsActivity.POST, allposts))
                    userPostList.add(UserPosts("Recommendation", "Recommendation is empty", UserPostsActivity.RECOMMEDATION, recommendedposts))
                    userPostList.add(UserPosts("WishList", "Wishlist is empty", UserPostsActivity.WISHLIST, wishlistposts))
                    return@Function4 UserWithPosts(user, userPostList)
                })
    }

    private fun getUserPosts(): Observable<MutableList<UserPosts>> {

        return userRepository.getUserDetailObservable(uid).flatMap { resource ->
            // do something with resource here.

            userRepository.getAllUserPosts(uid, 1).map {
                val userPostList = mutableListOf<UserPosts>()
                userPostList.add(UserPosts("Posts", "0 Posts", UserPostsActivity.POST, it))
                userPostList
            }
        }.flatMap { userPostList ->
            userRepository.getUserRecommededPosts(uid, 1).map {
                userPostList.add(UserPosts("Recommendation", "0 Recommendations", UserPostsActivity.RECOMMEDATION, it))
                 userPostList
            }

        }.flatMap { userPostList ->
            userRepository.getUserWishList(uid, 1).map {
                userPostList.add(UserPosts("WishList", "0 Wishlist", UserPostsActivity.WISHLIST, it))
                userPostList
            }
        }
    }

filter operators

filter
distinct
take
takeWhile

references

https://codingwithmitch.com/courses/rxjava-rxandroid-for-beginners
https://blog.mindorks.com/implement-search-using-rxjava-operators-c8882b64fe1d

Rx View Binding

RxView.clicks(post_detail_ib_recommendation).throttleFirst(2, TimeUnit.SECONDS)
        .subscribe {
                // your code
        }
RxView.clicks(post_detail_bt_follow).throttleFirst(2, TimeUnit.SECONDS)
        .subscribe {
                // your code
        }

search

@SuppressLint("CheckResult")
    private fun bindSearchAction() {
        Observable.create(ObservableOnSubscribe<String> { subscriber ->
            et_field.addTextChangedListener(object : TextWatcher {
                override fun afterTextChanged(s: Editable?) {
                    subscriber.onNext(s.toString())

                }

                override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
                    subscriber.onNext(s.toString())
                }

                override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
                    subscriber.onNext(s.toString())
                }
            })
        }).map { text -> text.toLowerCase().trim() }
                .debounce(250, TimeUnit.MILLISECONDS)
                .distinctUntilChanged()
                .filter { text -> text.isNotBlank() }
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe { text ->
                    searchForUser(text)
                }
    }

transformation operators

map
buffer
debounce
ThrottleFirst
flatMap
switchMap
concatMap