RxJava響應式編程之初級瞭解

時間 2019-11-11

標籤 rxjava 響應編程初級瞭解欄目 Java 简体版

原文原文鏈接

聽說如今流行的開發模式是 Retrofit+RxJava+MVP+ButterKnifephp

若是想要簡單學習ButterKnife、MVP模式，能夠參考我之前的例子
使用butterknife註解框架
 Android—MVP設計模式高級（三）java

今天我就簡單來學習下RxJava的相關知識
之前我也只是據說過RxJava，RxJava這個究竟是什麼東西呢？
呵呵，它實際上是一個庫，因此咱們使用裏面的方法，得須要下載庫，因此咱們須要在AS中進行配置react

1.RxJava 地址以及添加android

github地址：
https://github.com/ReactiveX/RxJava
或者
https://github.com/ReactiveX/RxAndroidgit

依賴庫添加：
compile ‘io.reactivex:rxjava:1.1.6’
或者
compile ‘io.reactivex:rxandroid:1.2.1’github

2.RxJava是什麼類型的庫？它的原理是什麼？數據庫

RxJava 在 GitHub 主頁上的自我介紹是「a library for composing asynchronous and event-based programs using observable sequences for the Java VM」（一個在 Java VM 上使用可觀測的序列來組成異步的、基於事件的程序的庫）。這就是 RxJava ，歸納得很是精準。編程

Rx：函數響應式編程，也許這個詞對你我都很只可意會，不可言傳，先拋開Rx不說，咱們接觸到的相似的這樣的思路，大概有接口回調、Handler通信、廣播通信、還有一個開源的EventBus、以及ContentPorivider裏面的觀察者模式、AsyncTask 咱們朦朧中也許就大概瞭解RxJava是怎麼個東西了。設計模式

RxJava 的異步實現，是經過一種擴展的觀察者模式來實現的。
至於觀察者我就拿ContentProvider來講吧，好比咱們在一個ContentProvider中有一個insert方法，插入完畢後，去通知某個監聽該URI變化的界面api

<code class="hljs avrasm has-numbering">getContext()<span class="hljs-preprocessor">.getContentResolver</span>()<span class="hljs-preprocessor">.notifyChange</span>(URI, null)<span class="hljs-comment">;</span></code><ul style="" class="pre-numbering"><li>1</li></ul><ul style="" class="pre-numbering"><li>1</li></ul>

好比在MainActivity中去registerContentObserver註冊一個內容觀察者

<code class="hljs java has-numbering"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> Uri URI = Uri  
            .parse(<span class="hljs-string">"content://com.example.contentprovider.MyContentProvider/student"</span>);  
 contentResolver.registerContentObserver(uri, <span class="hljs-keyword">true</span>, observer);</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li></ul>

<code class="hljs java has-numbering"> <span class="hljs-keyword">private</span> ContentObserver observer = <span class="hljs-keyword">new</span> ContentObserver(<span class="hljs-keyword">null</span>) {  
        <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onChange</span>(<span class="hljs-keyword">boolean</span> selfChange) {  
            <span class="hljs-comment">// 說明數據有改變,從新查詢一直全部記錄  </span>
            Uri uri = Uri.parse(<span class="hljs-string">"content://com.example.contentprovider.MyContentProvider/student"</span>);  
            Cursor cursor = contentResolver.query(uri, <span class="hljs-keyword">null</span>, <span class="hljs-keyword">null</span>, <span class="hljs-keyword">null</span>, <span class="hljs-keyword">null</span>);  
            Log.e(<span class="hljs-string">"TAG"</span>, <span class="hljs-string">"onChange()  count="</span> + cursor.getCount());  
        };  
    };  </code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li></ul>

那麼對於RxJava 的觀察者模式呢？
RxJava 有四個基本概念：Observable (被觀察者)、 Observer (觀察者)、 subscribe (訂閱)、事件。
對比ContentProvider，RxJava裏面的被觀察者就是某個Uri(也就是某個數據庫)，觀察者就是某個界面（好比MainActivity）,訂閱就是registerContentObserver，事件就是insert方法

Rxjava本質主要就是異步任務外層構建了一個觀察者的設計模式它更簡潔咱們調用api方法幾乎看不到方法裏面的分線程數據操做它只是利用了一種觀察者的設計模式來進行主分線程的通信來進行響應操做

咱們來看看RxJava的察者模式流程交互圖：

與傳統觀察者模式不一樣， RxJava 的事件回調方法除了普通事件 onNext() （至關於 insert）以外，還定義了兩個特殊的事件：onCompleted() 和 onError()。

咱們來看下Observable是如何定義的？

<code class="hljs avrasm has-numbering">     Observable<span class="hljs-preprocessor">.create</span>(new Observable<span class="hljs-preprocessor">.OnSubscribe</span><String>() {
            @Override
            public void <span class="hljs-keyword">call</span>(Subscriber<? super String> subscriber) {
                Log<span class="hljs-preprocessor">.d</span>(TAG, <span class="hljs-string">"call: threadId:"</span> + Thread<span class="hljs-preprocessor">.currentThread</span>()<span class="hljs-preprocessor">.getId</span>())<span class="hljs-comment">;</span>
                subscriber<span class="hljs-preprocessor">.onStart</span>()<span class="hljs-comment">;</span>
                subscriber<span class="hljs-preprocessor">.onNext</span>(<span class="hljs-string">"Hello World!"</span>)<span class="hljs-comment">;</span>
                subscriber<span class="hljs-preprocessor">.onCompleted</span>()<span class="hljs-comment">;</span>
            }
        })</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul>

咱們看看create源碼裏面作了什麼？

<code class="hljs cs has-numbering">   <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <T> Observable<T> <span class="hljs-title">create</span>(OnSubscribe<T> f) {
        <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> Observable<T>(hook.onCreate(f));
    }</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li></ul>

能夠看到，這裏傳入了一個 OnSubscribe 對象做爲參數。OnSubscribe 會被存儲在返回的 Observable 對象中，當 Observable 被訂閱的時候，OnSubscribe 的 call() 方法會自動被調用，事件序列就會依照設定依次觸發（對於上面的代碼，就是觀察者Subscriber 將會被調用一次 onNext() 和一次 onCompleted()）。這樣，由被觀察者調用了觀察者的回調方法，就實現了由被觀察者向觀察者的事件傳遞，即觀察者模式。

而後在看Observer中作了什麼操做？

<code class="hljs lasso has-numbering">subscribe(<span class="hljs-literal">new</span> Observer<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span>() {
                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onCompleted() {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>d(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onCompleted: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                    }

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onError(Throwable e) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>e(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onError: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                    }

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onNext(<span class="hljs-built_in">String</span> s) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>d(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onNext: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onNext: s = "</span> <span class="hljs-subst">+</span> s);
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li></ul>

onCompleted(): 事件隊列完結。RxJava 不只把每一個事件單獨處理，還會把它們看作一個隊列。RxJava 規定，當不會再有新的 onNext() 發出時，須要觸發 onCompleted() 方法做爲標誌。
onError(): 事件隊列異常。在事件處理過程當中出異常時，onError() 會被觸發，同時隊列自動終止，不容許再有事件發出。
在一個正確運行的事件序列中, onCompleted() 和 onError() 有且只有一個，而且是事件序列中的最後一個。須要注意的是，onCompleted() 和 onError() 兩者也是互斥的，即在隊列中調用了其中一個，就不該該再調用另外一個。

接下來咱們將所有的代碼貼出來，看看Log日誌打印：

同步方式

<code class="hljs java has-numbering"><span class="hljs-keyword">package</span> com.example.administrator.myapplication;
<span class="hljs-keyword">import</span> android.app.Activity;
<span class="hljs-keyword">import</span> android.os.Bundle;
<span class="hljs-keyword">import</span> android.util.Log;

<span class="hljs-keyword">import</span> rx.Observable;
<span class="hljs-keyword">import</span> rx.Observer;
<span class="hljs-keyword">import</span> rx.Subscriber;

<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MainActivity</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">Activity</span> {</span>
    <span class="hljs-keyword">private</span> String TAG = <span class="hljs-string">"MainActivity"</span>;
    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCreate</span>(Bundle savedInstanceState) {
        <span class="hljs-keyword">super</span>.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Observable.create(<span class="hljs-keyword">new</span> Observable.OnSubscribe<String>() {
            <span class="hljs-annotation">@Override</span>
            <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">call</span>(Subscriber<? <span class="hljs-keyword">super</span> String> subscriber) {
                Log.d(TAG, <span class="hljs-string">"call: threadId:"</span> + Thread.currentThread().getId());
                subscriber.onStart();
                subscriber.onNext(<span class="hljs-string">"Hello World!"</span>);
                subscriber.onCompleted();
            }
        })
                .subscribe(<span class="hljs-keyword">new</span> Observer<String>() {
                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCompleted</span>() {
                        Log.d(TAG, <span class="hljs-string">"onCompleted: threadId:"</span> + Thread.currentThread().getId());
                    }

                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onError</span>(Throwable e) {
                        Log.e(TAG, <span class="hljs-string">"onError: threadId:"</span> + Thread.currentThread().getId());
                    }

                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onNext</span>(String s) {
                        Log.d(TAG, <span class="hljs-string">"onNext: threadId:"</span> + Thread.currentThread().getId());
                        Log.i(TAG, <span class="hljs-string">"onNext: s = "</span> + s);
                    }
                });
    }
}
</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li><li>29</li><li>30</li><li>31</li><li>32</li><li>33</li><li>34</li><li>35</li><li>36</li><li>37</li><li>38</li><li>39</li><li>40</li><li>41</li><li>42</li><li>43</li><li>44</li><li>45</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li><li>29</li><li>30</li><li>31</li><li>32</li><li>33</li><li>34</li><li>35</li><li>36</li><li>37</li><li>38</li><li>39</li><li>40</li><li>41</li><li>42</li><li>43</li><li>44</li><li>45</li></ul>

<code class="hljs http has-numbering"><span class="hljs-attribute">call</span>: <span class="hljs-string">threadId:1</span>
<span class="hljs-attribute">onNext</span>: <span class="hljs-string">threadId:1</span>
<span class="hljs-attribute">onNext</span>: <span class="hljs-string">s = Hello World!</span>
<span class="hljs-attribute">onCompleted</span>: <span class="hljs-string">threadId:1</span></code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li></ul>

從上能夠看出，事件的處理和結果的接收都是在同一個線程裏面處理的。可是，Rxjava的意義何在，異步呢？別急，看如下代碼的處理，你就會發現了，異步原來是這麼的簡單。
異步方式
咱們將上面的代碼稍微改下，增長2行代碼

<code class="hljs lasso has-numbering">        Observable<span class="hljs-built_in">.</span>create(<span class="hljs-literal">new</span> Observable<span class="hljs-built_in">.</span>OnSubscribe<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span>() {
            @Override
            <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> call(Subscriber<span class="hljs-subst"><?</span> super <span class="hljs-built_in">String</span><span class="hljs-subst">></span> subscriber) {
                <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>d(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"call: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                subscriber<span class="hljs-built_in">.</span>onStart();
                subscriber<span class="hljs-built_in">.</span>onNext(<span class="hljs-string">"Hello World!"</span>);
                subscriber<span class="hljs-built_in">.</span>onCompleted();
            }
        })
                <span class="hljs-built_in">.</span>subscribeOn(Schedulers<span class="hljs-built_in">.</span>io())
                <span class="hljs-built_in">.</span>observeOn(AndroidSchedulers<span class="hljs-built_in">.</span>mainThread())
                <span class="hljs-built_in">.</span>subscribe(<span class="hljs-literal">new</span> Observer<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span>() {
                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onCompleted() {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>d(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onCompleted: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                    }

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onError(Throwable e) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>e(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onError: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                    }

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onNext(<span class="hljs-built_in">String</span> s) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>d(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onNext: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onNext: s = "</span> <span class="hljs-subst">+</span> s);
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li></ul>

咱們添上以下2行代碼

<code class="hljs avrasm has-numbering"><span class="hljs-preprocessor">.subscribeOn</span>(Schedulers<span class="hljs-preprocessor">.io</span>())
<span class="hljs-preprocessor">.observeOn</span>(AndroidSchedulers<span class="hljs-preprocessor">.mainThread</span>())</code><ul style="" class="pre-numbering"><li>1</li><li>2</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li></ul>

咱們看下Log輸出

<code class="hljs mathematica has-numbering"><span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">07</span>:<span class="hljs-number">20</span>:<span class="hljs-number">18.101</span> <span class="hljs-number">22734</span>-<span class="hljs-number">22734</span>/? <span class="hljs-keyword">I</span>/MainActivity: testFunction: threadId:<span class="hljs-number">1</span>
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">07</span>:<span class="hljs-number">20</span>:<span class="hljs-number">18.123</span> <span class="hljs-number">22734</span>-<span class="hljs-number">22755</span>/? <span class="hljs-keyword">D</span>/MainActivity: call: threadId:<span class="hljs-number">180</span>
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">07</span>:<span class="hljs-number">20</span>:<span class="hljs-number">18.142</span> <span class="hljs-number">22734</span>-<span class="hljs-number">22734</span>/? <span class="hljs-keyword">D</span>/MainActivity: onNext: threadId:<span class="hljs-number">1</span>
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">07</span>:<span class="hljs-number">20</span>:<span class="hljs-number">18.142</span> <span class="hljs-number">22734</span>-<span class="hljs-number">22734</span>/? <span class="hljs-keyword">I</span>/MainActivity: onNext: s = Hello World!
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">07</span>:<span class="hljs-number">20</span>:<span class="hljs-number">18.143</span> <span class="hljs-number">22734</span>-<span class="hljs-number">22734</span>/? <span class="hljs-keyword">D</span>/MainActivity: onCompleted: threadId:<span class="hljs-number">1</span></code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li></ul>

看見了沒，第二行log日誌threadId與其它的threadId很明顯的不同啊，說明咱們在處理事件的時候，發生在了一個新的線程裏面，而結果的接收，仍是在主線程裏面操做的。怎麼樣，只要添加兩句話，異步立馬就實現了，異步處理耗時操做，就是這麼easy。

咱們簡單看下源碼

<code class="hljs java has-numbering"> <span class="hljs-keyword">public</span> <span class="hljs-keyword">final</span> Observable<T> <span class="hljs-title">subscribeOn</span>(Scheduler scheduler) {
        <span class="hljs-keyword">if</span> (<span class="hljs-keyword">this</span> <span class="hljs-keyword">instanceof</span> ScalarSynchronousObservable) {
            <span class="hljs-keyword">return</span> ((ScalarSynchronousObservable<T>)<span class="hljs-keyword">this</span>).scalarScheduleOn(scheduler);
        }
        <span class="hljs-keyword">return</span> create(<span class="hljs-keyword">new</span> OperatorSubscribeOn<T>(<span class="hljs-keyword">this</span>, scheduler));
    }</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li></ul>

什麼意思呢？
Scheduler scheduler參數就是執行訂閱操做，返回一個源觀察到的修改，使其訂閱發生在指定的線程
observeOn(AndroidSchedulers.mainThread())
句話說，observeOn() 指定的是它以後的操做所在的線程。

打印字符串數組 from和just方式

以上是RxJava的很基礎很簡單的一個用法，那麼咱們接着往下看，好比咱們有一組需求把一個String數組的字符串，單個打印出來，咱們用Rxjava怎麼實現呢？看代碼：

<code class="hljs java has-numbering">Log.i(TAG, <span class="hljs-string">"testFunction: threadId:"</span> + Thread.currentThread().getId());
        Observable.from(<span class="hljs-keyword">new</span> String[]{<span class="hljs-string">"one"</span>,<span class="hljs-string">"two"</span>,<span class="hljs-string">"three"</span>,<span class="hljs-string">"four"</span>})
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(<span class="hljs-keyword">new</span> Observer<String>() {
                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCompleted</span>() {
                        Log.d(TAG, <span class="hljs-string">"onCompleted: threadId:"</span> + Thread.currentThread().getId());
                    }

                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onError</span>(Throwable e) {
                        Log.e(TAG, <span class="hljs-string">"onError: threadId:"</span> + Thread.currentThread().getId());
                    }

                    <span class="hljs-annotation">@Override</span>
                    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onNext</span>(String s) {
                        Log.i(TAG, <span class="hljs-string">"onNext: s = "</span> + s);
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li></ul>

看Log輸出日誌以下：

<code class="hljs http has-numbering"><span class="hljs-attribute">testFunction</span>: <span class="hljs-string">threadId:1</span>
<span class="hljs-attribute">onNext</span>: <span class="hljs-string">s = one</span>
<span class="hljs-attribute">onNext</span>: <span class="hljs-string">s = two</span>
<span class="hljs-attribute">onNext</span>: <span class="hljs-string">s = three</span>
<span class="hljs-attribute">onNext</span>: <span class="hljs-string">s = four</span>
<span class="hljs-attribute">onCompleted</span>: <span class="hljs-string">threadId:1</span>
</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li></ul>

From操做符用來將某個對象轉化爲Observable對象，而且依次將其內容發射出去。這個相似於just，可是just會將這個對象整個發射出去。好比說一個含有3個字符串的數組，使用from就會發射4次，每次發射一個數字，而使用just會發射一次來將整個的數組發射出去。

<code class="hljs lasso has-numbering"> <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"testFunction: threadId:"</span><span class="hljs-subst">+</span><span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
        Observable<span class="hljs-built_in">.</span>just(<span class="hljs-string">"one"</span>, <span class="hljs-string">"two"</span>, <span class="hljs-string">"three"</span>, <span class="hljs-string">"four"</span>)
                <span class="hljs-built_in">.</span>subscribeOn(Schedulers<span class="hljs-built_in">.</span>io())
                <span class="hljs-built_in">.</span>observeOn(AndroidSchedulers<span class="hljs-built_in">.</span>mainThread())
                <span class="hljs-built_in">.</span>subscribe(<span class="hljs-literal">new</span> Observer<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span>() {
                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onCompleted() {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>d(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onCompleted: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                    }

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onError(Throwable e) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>e(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onError: threadId:"</span> <span class="hljs-subst">+</span> <span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
                    }

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> onNext(<span class="hljs-built_in">String</span> s) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"onNext: s = "</span> <span class="hljs-subst">+</span> s);
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li></ul>

<code class="hljs mathematica has-numbering"><span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">08</span>:<span class="hljs-number">09</span>:<span class="hljs-number">25.743</span> <span class="hljs-number">32155</span>-<span class="hljs-number">32155</span>/? <span class="hljs-keyword">I</span>/MainActivity: testFunction: threadId:<span class="hljs-number">1</span>
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">08</span>:<span class="hljs-number">09</span>:<span class="hljs-number">25.784</span> <span class="hljs-number">32155</span>-<span class="hljs-number">32155</span>/? <span class="hljs-keyword">I</span>/MainActivity: onNext: s = one
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">08</span>:<span class="hljs-number">09</span>:<span class="hljs-number">25.785</span> <span class="hljs-number">32155</span>-<span class="hljs-number">32155</span>/? <span class="hljs-keyword">I</span>/MainActivity: onNext: s = two
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">08</span>:<span class="hljs-number">09</span>:<span class="hljs-number">25.785</span> <span class="hljs-number">32155</span>-<span class="hljs-number">32155</span>/? <span class="hljs-keyword">I</span>/MainActivity: onNext: s = three
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">08</span>:<span class="hljs-number">09</span>:<span class="hljs-number">25.785</span> <span class="hljs-number">32155</span>-<span class="hljs-number">32155</span>/? <span class="hljs-keyword">I</span>/MainActivity: onNext: s = four
<span class="hljs-number">03</span>-<span class="hljs-number">08</span> <span class="hljs-number">08</span>:<span class="hljs-number">09</span>:<span class="hljs-number">25.785</span> <span class="hljs-number">32155</span>-<span class="hljs-number">32155</span>/? <span class="hljs-keyword">D</span>/MainActivity: onCompleted: threadId:<span class="hljs-number">1</span>
</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li></ul>

一對一轉換

<code class="hljs lasso has-numbering"> <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"testFunction: threadId:"</span><span class="hljs-subst">+</span><span class="hljs-keyword">Thread</span><span class="hljs-built_in">.</span>currentThread()<span class="hljs-built_in">.</span>getId());
        Observable<span class="hljs-built_in">.</span>just(<span class="hljs-string">"1"</span>, <span class="hljs-string">"2"</span>, <span class="hljs-string">"3"</span>, <span class="hljs-string">"4"</span>)
                <span class="hljs-built_in">.</span>subscribeOn(Schedulers<span class="hljs-built_in">.</span>io())
                <span class="hljs-built_in">.</span>observeOn(AndroidSchedulers<span class="hljs-built_in">.</span>mainThread())
                <span class="hljs-built_in">.</span><span class="hljs-built_in">map</span>(<span class="hljs-literal">new</span> Func1<span class="hljs-subst"><</span><span class="hljs-built_in">String</span>, <span class="hljs-built_in">Integer</span><span class="hljs-subst">></span>() {

                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-built_in">Integer</span> call(<span class="hljs-built_in">String</span> s) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"call: s = "</span><span class="hljs-subst">+</span>s);
                        <span class="hljs-keyword">return</span> <span class="hljs-built_in">Integer</span><span class="hljs-built_in">.</span>parseInt(s);
                    }
                })
                <span class="hljs-built_in">.</span>subscribe(<span class="hljs-literal">new</span> Action1<span class="hljs-subst"><</span><span class="hljs-built_in">Integer</span><span class="hljs-subst">></span>() {
                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> call(<span class="hljs-built_in">Integer</span> <span class="hljs-built_in">integer</span>) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"call: integer = "</span><span class="hljs-subst">+</span><span class="hljs-built_in">integer</span>);
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li></ul>

<code class="hljs http has-numbering"><span class="hljs-attribute">testFunction</span>: <span class="hljs-string">threadId:1</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">s = 1</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">integer = 1</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">s = 2</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">integer = 2</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">s = 3</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">integer = 3</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">s = 4</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">integer = 4</span></code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul>

簡單說一下Func1，其中的T表示傳入的參數類型，R表示方法返回的參數類型。源碼以下：

<code class="hljs php has-numbering"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">Func1</span><<span class="hljs-title">T</span>, <span class="hljs-title">R</span>> <span class="hljs-keyword">extends</span> <span class="hljs-title">Function</span> {</span>
    R call(T t);
}
</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li></ul>

上例中還有一個叫作 Action1的類。也是 RxJava 的一個接口，用於包裝含有無參數的方法。 Func1 和 Action 的區別在於， Func1 包裝的是有返回值的方法。另外，和 ActionX 同樣， FuncX 也有多個，用於不一樣參數個數的方法。FuncX 和 ActionX 的區別在 FuncX 包裝的是有返回值的方法。

能夠看到，map() 方法將參數中的 String 對象轉換成一個 Integer對象後返回，而在通過 map() 方法後，事件的參數類型也由 String 轉爲了 Integer。這種直接變換對象並返回的，是最多見的也最容易理解的變換。不過 RxJava 的變換遠不止這樣，它不只能夠針對事件對象，還能夠針對整個事件隊列，這使得 RxJava 變得很是靈活。

封裝Observable一對多轉換
map轉換，是一對一的轉換，像示例當中，咱們把string轉成int，可是當咱們須要一對多的轉換，該怎麼作呢？好比說，定義一個學生類：

<code class="hljs cs has-numbering">package com.example.administrator.myapplication;

import java.util.List;

<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> Student {

    <span class="hljs-keyword">private</span> String name;

    <span class="hljs-keyword">public</span> String <span class="hljs-title">getName</span>() {
        <span class="hljs-keyword">return</span> name;
    }

    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setName</span>(String name) {
        <span class="hljs-keyword">this</span>.name = name;
    }

    <span class="hljs-comment"><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span><span class="hljs-xmlDocTag">///</span>//</span>
    <span class="hljs-keyword">private</span> List<String> courses;


    <span class="hljs-keyword">public</span> List<String> <span class="hljs-title">getCourses</span>() {
        <span class="hljs-keyword">return</span> courses;
    }

    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setCourses</span>(List<String> courses) {
        <span class="hljs-keyword">this</span>.courses = courses;
    }
}</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li></ul>

<code class="hljs lasso has-numbering">
        Student student1 <span class="hljs-subst">=</span> <span class="hljs-literal">new</span> Student();
        student1<span class="hljs-built_in">.</span>setName(<span class="hljs-string">"safly"</span>);
        <span class="hljs-built_in">List</span><span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span> courses <span class="hljs-subst">=</span> <span class="hljs-literal">new</span> ArrayList<span class="hljs-subst"><></span>();
        courses<span class="hljs-built_in">.</span>add(<span class="hljs-string">"語文"</span>);
        courses<span class="hljs-built_in">.</span>add(<span class="hljs-string">"數學"</span>);
        courses<span class="hljs-built_in">.</span>add(<span class="hljs-string">"英語"</span>);
        student1<span class="hljs-built_in">.</span>setCourses(courses);

        Student student2 <span class="hljs-subst">=</span> <span class="hljs-literal">new</span> Student();
        student2<span class="hljs-built_in">.</span>setName(<span class="hljs-string">"wyf"</span>);
        <span class="hljs-built_in">List</span><span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span> courses2 <span class="hljs-subst">=</span> <span class="hljs-literal">new</span> ArrayList<span class="hljs-subst"><></span>();
        courses2<span class="hljs-built_in">.</span>add(<span class="hljs-string">"化學"</span>);
        courses2<span class="hljs-built_in">.</span>add(<span class="hljs-string">"地理"</span>);
        courses2<span class="hljs-built_in">.</span>add(<span class="hljs-string">"政治"</span>);
        student2<span class="hljs-built_in">.</span>setCourses(courses2);



        Observable<span class="hljs-built_in">.</span>just(student1,student2)
                <span class="hljs-built_in">.</span>subscribe(<span class="hljs-literal">new</span> Action1<span class="hljs-subst"><</span>Student<span class="hljs-subst">></span>() {
                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> call(Student student) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"call: name = "</span><span class="hljs-subst">+</span>student<span class="hljs-built_in">.</span>getName());
                        <span class="hljs-built_in">List</span><span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span> course <span class="hljs-subst">=</span> student<span class="hljs-built_in">.</span>getCourses();
                        for(<span class="hljs-built_in">String</span> str:course){
                            <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"call: str = "</span><span class="hljs-subst">+</span>str);
                        }
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li><li>29</li><li>30</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li><li>15</li><li>16</li><li>17</li><li>18</li><li>19</li><li>20</li><li>21</li><li>22</li><li>23</li><li>24</li><li>25</li><li>26</li><li>27</li><li>28</li><li>29</li><li>30</li></ul>

這裏咱們沒有進行轉換，直接just發送過來，沒有用到轉換，而後在call中進行直接輸出了

<code class="hljs http has-numbering"><span class="hljs-attribute">call</span>: <span class="hljs-string">name = safly</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">str = 語文</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">str = 數學</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">str = 英語</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">name = wyf</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">str = 化學</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">str = 地理</span>
<span class="hljs-attribute">call</span>: <span class="hljs-string">str = 政治</span>
</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul>

咱們用轉換來試試看？
這裏咱們用到了flatmap這一函數，按通俗的一點理解：咱們首先把Student轉成了Observable，而後呢，又把student.getCourses()轉成string挨個打印出來，結果以下：

<code class="hljs lasso has-numbering"> Observable<span class="hljs-built_in">.</span>just(student1,student2)
                  <span class="hljs-built_in">.</span>flatMap(<span class="hljs-literal">new</span> Func1<span class="hljs-subst"><</span>Student, Observable<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">>></span>() {
                      @Override
                      <span class="hljs-keyword">public</span> Observable<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span> call(Student student) {
                       <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"Observable "</span> );
                          <span class="hljs-keyword">return</span> Observable<span class="hljs-built_in">.</span>from(student<span class="hljs-built_in">.</span>getCourses());
                      }
                  })
                <span class="hljs-built_in">.</span>subscribe(<span class="hljs-literal">new</span> Action1<span class="hljs-subst"><</span><span class="hljs-built_in">String</span><span class="hljs-subst">></span>() {
                    @Override
                    <span class="hljs-keyword">public</span> <span class="hljs-literal">void</span> call(<span class="hljs-built_in">String</span> s) {
                        <span class="hljs-keyword">Log</span><span class="hljs-built_in">.</span>i(<span class="hljs-built_in">TAG</span>, <span class="hljs-string">"call: s = "</span><span class="hljs-subst">+</span>s);     
                    }
                });</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li><li>10</li><li>11</li><li>12</li><li>13</li><li>14</li></ul>

輸出

<code class="hljs vbnet has-numbering"> Observable
<span class="hljs-keyword">call</span>: s = 語文
<span class="hljs-keyword">call</span>: s = 數學
<span class="hljs-keyword">call</span>: s = 英語
 Observable
<span class="hljs-keyword">call</span>: s = 化學
<span class="hljs-keyword">call</span>: s = 地理
<span class="hljs-keyword">call</span>: s = 政治<span id="transmark"></span>
</code><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul><ul style="" class="pre-numbering"><li>1</li><li>2</li><li>3</li><li>4</li><li>5</li><li>6</li><li>7</li><li>8</li><li>9</li></ul>

咱們還記得Observable.from嘛？
From操做符用來將某個對象轉化爲Observable對象

<code class="hljs cs has-numbering">  <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <T> Observable<T> <span class="hljs-title">from</span>(Iterable<? extends T> iterable) {
        <span class="hljs-keyword">return</span> create(<span class="hljs-keyword">new</span> OnSubscribeFromIterable<T>(iterable));
    }</code>