android - RxJava 不在后台线程上运行

Question

我正在尝试在 Room 中保存数据，它需要一些后台线程来保存数据。所以我创建了一个这样的可观察对象

val obs: Observable<MutableLiveData<List<Source>>>? = Observable.fromCallable(object :Callable<MutableLiveData<List<Source>>>{
            override fun call(): MutableLiveData<List<Source>> {

                return mutableLiveData
            }
        })

然后我就这样订阅，观察，退订

obs?.subscribeOn(Schedulers.io())?.observeOn(AndroidSchedulers.mainThread())?.unsubscribeOn(Schedulers.io())
                ?.subscribe(object : Observer<MutableLiveData<List<Source>>>{
                    override fun onComplete() {

                    }

                    override fun onSubscribe(d: Disposable?) {

                    }

                    override fun onNext(value: MutableLiveData<List<Source>>?) {
                        for(source in value!!.value!!.iterator()){
                            sourceDao.insert(source)//this is the line number 87, that logcat is pointing
                        }
                    }

                    override fun onError(e: Throwable?) {
                        e?.printStackTrace()
                    }
                })

我在 Schedulers.io 线程上订阅它，然后在 AndroidSchedulers.mainThread() 上观察它，但我仍然没有收到后台线程错误。更具体地说

    Caused by: java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.
        at android.arch.persistence.room.RoomDatabase.assertNotMainThread(RoomDatabase.java:204)
        at android.arch.persistence.room.RoomDatabase.beginTransaction(RoomDatabase.java:251)
06-18 11:11:08.674 3732-3732/com.theanilpaudel.technewspro W/System.err:     at com.package.myapp.room.SourceDao_Impl.insert(SourceDao_Impl.java:63)
        at com.package.myapp.main.MainRepository$saveToRoom$1.onNext(MainRepository.kt:87)
        at com.package.myapp.main.MainRepository$saveToRoom$1.onNext(MainRepository.kt:76)

Answer 1

在 Observable 中执行您的数据库操作，而不是在您的观察者中:

val obs: Observable<MutableLiveData<List<Source>>>? = Observable.fromCallable(object :Callable<MutableLiveData<List<Source>>>{
        override fun call(): MutableLiveData<List<Source>> {
             for(source in mutableLiveData!!.value!!.iterator()){
                  sourceDao.insert(source)
             }
            return mutableLiveData
        })
        .subscribeOn(Schedulers.io())?.observeOn(AndroidSchedulers.mainThread())?.unsubscribeOn(Schedulers.io())
            ?.subscribe(object : Observer<MutableLiveData<List<Source>>>{
                override fun onComplete() {

                }

                override fun onSubscribe(d: Disposable?) {

                }

                override fun onNext(value: MutableLiveData<List<Source>>?) {
                    // Nothing todo right more
                }

                override fun onError(e: Throwable?) {
                    e?.printStackTrace()
                }
            })
    })