我想知道是否有人可以闡明這個(gè)問(wèn)題，何時(shí)使用Single.fromCallable( ()-> myObject )代替Single.just(myObject)從文檔中，Single.fromCallable()： /** * Returns a {@link Single} that invokes passed function and emits its result for each new SingleObserver that subscribes. * <p> * Allows you to defer execution of passed function until SingleObserver subscribes to the {@link Single}. * It makes passed function "lazy". * Result of the function invocation will be emitted by the {@link Single}. * <dl> * <dt><b>Scheduler:</b></dt> * <dd>{@code fromCallable} does not operate by default on a particular {@link Scheduler}.</dd> * </dl> * * @param callable * function which execution should be deferred, it will be invoked when SingleObserver will subscribe to the {@link Single}. * @param <T> * the type of the item emitted by the {@link Single}. * @return a {@link Single} whose {@link SingleObserver}s' subscriptions trigger an invocation of the given function. */和文檔Single.just()： /** * Returns a {@code Single} that emits a specified item. * <p> * <img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.just.png" alt=""> * <p> * To convert any object into a {@code Single} that emits that object, pass that object into the * {@code just} method. * <dl> * <dt><b>Scheduler:</b></dt> * <dd>{@code just} does not operate by default on a particular {@link Scheduler}.</dd> * </dl> * * @param item * the item to emit * @param <T> * the type of that item * @return a {@code Single} that emits {@code item} * @see <a href="http://reactivex.io/documentation/operators/just.html">ReactiveX operators documentation: Just</a> */
3 回答
慕標(biāo)琳琳
TA貢獻(xiàn)1830條經(jīng)驗(yàn) 獲得超9個(gè)贊
在您提到的用例中，實(shí)際上沒(méi)有重大區(qū)別。
現(xiàn)在想象一下我們需要通過(guò)函數(shù)調(diào)用動(dòng)態(tài)創(chuàng)建對(duì)象嗎？
fun getTimeObject() {
val timeInMillis = System.currentTimeMillis()
return TimeObject(timeInMillis)
}
然后，當(dāng)它有一個(gè)新訂閱者時(shí)，Single.just(getTimeObject())結(jié)果Single將發(fā)出相同的信息Long。
然而，當(dāng)它有一個(gè)新訂閱者時(shí)Single.fromcallable(()-> getTimeObject())，結(jié)果Single將發(fā)出一個(gè)不同的Long指示以毫秒為單位的當(dāng)前時(shí)間。
那是因?yàn)閒romCallable每當(dāng)它有一個(gè)新訂閱者Lazily 時(shí)，它就會(huì)執(zhí)行它的 lambda 。
青春有我
TA貢獻(xiàn)1784條經(jīng)驗(yàn) 獲得超8個(gè)贊
當(dāng)你有一個(gè)類似的函數(shù)時(shí)，你應(yīng)該使用fromCallable()
MyObject myFunction() {
// some login here
return new MyObject();
}
然后你可以像這樣從這個(gè)函數(shù)創(chuàng)建Single：
Single.fromCallable(() -> myFunction());
Single.just(myObject)只是在沒(méi)有任何邏輯的情況下發(fā)出您的對(duì)象。
因此，當(dāng)您想要發(fā)出特定項(xiàng)目時(shí)，無(wú)需使用fromCallable()。
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