這一節解釋[`ConnectableObservable`](http://reactivex.io/RxJava/javadoc/rx/observables/ConnectableObservable.html) 和它的子類以及它們的操作符： * [**`ConnectableObservable.connect(?)`**](Connect.md) — 指示一個可連接的Observable開始發射數據 * [**`Observable.publish(?)`**](Publish.md) — 將一個Observable轉換為一個可連接的Observable * [**`Observable.replay(?)`**](Replay.md) — 確保所有的訂閱者看到相同的數據序列，即使它們在Observable開始發射數據之后才訂閱 * [**`ConnectableObservable.refCount(?)`**](RefCount.md) — 讓一個可連接的Observable表現得像一個普通的Observable 一個可連接的Observable與普通的Observable差不多，除了這一點：可連接的Observable在被訂閱時并不開始發射數據，只有在它的`connect()`被調用時才開始。用這種方法，你可以等所有的潛在訂閱者都訂閱了這個Observable之后才開始發射數據。  The following example code shows two Subscribers subscribing to the same Observable. In the first case, they subscribe to an ordinary Observable; in the second case, they subscribe to a Connectable Observable that only connects after both Subscribers subscribe. Note the difference in the output: 下面的示例代碼展示了兩個訂閱者訂閱同一個Observable的情況。第一種情形，它們訂閱一個普通的Observable；第二種情形，它們訂閱一個可連接的Observable，并且在兩個都訂閱后再連接。注意輸出的不同： **示例 #1:** ```groovy def firstMillion = Observable.range( 1, 1000000 ).sample(7, java.util.concurrent.TimeUnit.MILLISECONDS); firstMillion.subscribe( { println("Subscriber #1:" + it); }, // onNext { println("Error: " + it.getMessage()); }, // onError { println("Sequence #1 complete"); } // onCompleted ); firstMillion.subscribe( { println("Subscriber #2:" + it); }, // onNext { println("Error: " + it.getMessage()); }, // onError { println("Sequence #2 complete"); } // onCompleted ); ``` ``` Subscriber #1:211128 Subscriber #1:411633 Subscriber #1:629605 Subscriber #1:841903 Sequence #1 complete Subscriber #2:244776 Subscriber #2:431416 Subscriber #2:621647 Subscriber #2:826996 Sequence #2 complete ``` **示例 #2:** ```groovy def firstMillion = Observable.range( 1, 1000000 ).sample(7, java.util.concurrent.TimeUnit.MILLISECONDS).publish(); firstMillion.subscribe( { println("Subscriber #1:" + it); }, // onNext { println("Error: " + it.getMessage()); }, // onError { println("Sequence #1 complete"); } // onCompleted ); firstMillion.subscribe( { println("Subscriber #2:" + it); }, // onNext { println("Error: " + it.getMessage()); }, // onError { println("Sequence #2 complete"); } // onCompleted ); firstMillion.connect(); ``` ``` Subscriber #2:208683 Subscriber #1:208683 Subscriber #2:432509 Subscriber #1:432509 Subscriber #2:644270 Subscriber #1:644270 Subscriber #2:887885 Subscriber #1:887885 Sequence #2 complete Sequence #1 complete ``` #### 參見： * <a href="http://reactivex.io/RxJava/javadoc/rx/observables/ConnectableObservable.html">`ConnectableObservable`</a> * <a href="http://www.introtorx.com/Content/v1.0.10621.0/14_HotAndColdObservables.html#PublishAndConnect">Introduction to Rx: Publish and Connect</a>