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RxSwift快速指南(四)
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<h1 id="Combine"><a href="#Combine" class="headerlink" title="Combine"></a>Combine</h1><p>有时数据源并不只一个，比如用户登录，我们需要将用户名和密码进行合并验证，这时我们可以使用RxSwift为我们提供的合并，<code>combineLatest</code>, <code>merge</code>, <code>startWith</code>, <code>switchLatest</code>和<code>zip</code>等。</p>
<h2 id="combineLatest"><a href="#combineLatest" class="headerlink" title="combineLatest"></a>combineLatest</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line">example(<span class="string">"combineLatest"</span>) {</span><br><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> stringSubject = <span class="type">PublishSubject</span><<span class="type">String</span>>()</span><br><span class="line"><span class="keyword">let</span> intSubject = <span class="type">PublishSubject</span><<span class="type">Int</span>>()</span><br><span class="line"></span><br><span class="line"><span class="type">Observable</span>.combineLatest(stringSubject, intSubject) { stringElement, intElement <span class="keyword">in</span></span><br><span class="line"> <span class="string">"<span class="subst">\(stringElement)</span> <span class="subst">\(intElement)</span>"</span></span><br><span class="line"> }</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br><span class="line"></span><br><span class="line">stringSubject.onNext(<span class="string">"A"</span>)</span><br><span class="line">stringSubject.onNext(<span class="string">"B"</span>)</span><br><span class="line">intSubject.onNext(<span class="number">1</span>)</span><br><span class="line">intSubject.onNext(<span class="number">2</span>)</span><br><span class="line">stringSubject.onNext(<span class="string">"AB"</span>)</span><br><span class="line">intSubject.onNext(<span class="number">3</span>)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>combineLatest</code>和<code>zip</code>比较像，通过一个resultSelector的closure，将不同队列中的Element进行合并，最终队列Element的数量是当所有队列都有值后，这些队列在出现的Element数量加一。</p>
<h2 id="merge"><a href="#merge" class="headerlink" title="merge"></a>merge</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> subject1 = <span class="type">PublishSubject</span><<span class="type">String</span>>()</span><br><span class="line"><span class="keyword">let</span> subject2 = <span class="type">PublishSubject</span><<span class="type">String</span>>()</span><br><span class="line"></span><br><span class="line"><span class="type">Observable</span>.of(subject1, subject2)</span><br><span class="line"> .merge()</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br><span class="line"></span><br><span class="line">subject1.onNext(<span class="string">"A"</span>)</span><br><span class="line">subject1.onNext(<span class="string">"B"</span>)</span><br><span class="line">subject2.onNext(<span class="string">"1"</span>)</span><br><span class="line">subject2.onNext(<span class="string">"2"</span>)</span><br><span class="line">subject1.onNext(<span class="string">"AB"</span>)</span><br><span class="line">subject2.onNext(<span class="string">"3"</span>)</span><br></pre></td></tr></table></figure>
<p><code>merge</code>将所有队列中的元素按照出现的顺序合并到一个队列中去。</p>
<h2 id="startWith"><a href="#startWith" class="headerlink" title="startWith"></a>startWith</h2><p><code>startWith</code>用于在一个队列前加入一些Elements。</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="type">Observable</span>.of(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>)</span><br><span class="line"> .startWith(<span class="string">"A"</span>)</span><br><span class="line"> .startWith(<span class="string">"B"</span>, <span class="string">"C"</span>, <span class="string">"D"</span>)</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">startWith</span><span class="params">(elements: E ...)</span></span> -> <span class="type">Observable</span><<span class="type">E</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">StartWith</span>(source: <span class="keyword">self</span>.asObservable(), elements: elements)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>elements</code>这里是一个可变参数，可接受一个或者多个元素，需要注意的是如果在Observable中加入debug信息，后加入的Element并不在Next Event里，这可能会给你的调试带来一些麻烦，可能这是一个Debug和Producer在一起的bug。</p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">--- startWith example ---</span><br><span class="line">B</span><br><span class="line">C</span><br><span class="line">D</span><br><span class="line">A</span><br><span class="line">2016-07-06 19:40:31.382: startWith -> subscribed</span><br><span class="line">2016-07-06 19:40:31.383: startWith -> Event Next(1)</span><br><span class="line">1</span><br><span class="line">2016-07-06 19:40:31.383: startWith -> Event Next(2)</span><br><span class="line">2</span><br><span class="line">2016-07-06 19:40:31.383: startWith -> Event Next(3)</span><br><span class="line">3</span><br><span class="line">2016-07-06 19:40:31.384: startWith -> Event Next(4)</span><br><span class="line">4</span><br><span class="line">2016-07-06 19:40:31.384: startWith -> Event Completed</span><br><span class="line">2016-07-06 19:40:31.384: startWith -> disposed</span><br></pre></td></tr></table></figure>
<h2 id="switchLatest"><a href="#switchLatest" class="headerlink" title="switchLatest"></a>switchLatest</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="type">Observable</span>.range(start: <span class="number">0</span>, <span class="built_in">count</span>: <span class="number">3</span>)</span><br><span class="line"> .<span class="built_in">map</span> { <span class="type">Observable</span>.range(start: $<span class="number">0</span>, <span class="built_in">count</span>: <span class="number">3</span>) }</span><br><span class="line"> .switchLatest()</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<p>map后再switchLatest其实和flatMapLatest的结果是一样的，需要理解的是switch队列以后，以前队列的Element将不在发送。</p>
<img src="/2016/07/05/quick-guide-for-RxSwift-four/switchLatest.png" alt="switchLatest" title="switchLatest">
<h2 id="zip"><a href="#zip" class="headerlink" title="zip"></a>zip</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> range = <span class="type">Observable</span>.range(start: <span class="number">0</span>, <span class="built_in">count</span>: <span class="number">5</span>);</span><br><span class="line"><span class="type">Observable</span>.<span class="built_in">zip</span>(range, range.skip(<span class="number">1</span>), range.skip(<span class="number">2</span>)) { <span class="string">"<span class="subst">\($<span class="number">0</span>)</span>:<span class="subst">\($<span class="number">1</span>)</span>:<span class="subst">\($<span class="number">2</span>)</span>"</span> }</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<p><code>zip</code>可以和<code>combineLatest</code>对比理解，zip每次在每个队列中取一个元素进行处理，元素在对应的队列中index是一样，产生的Element数量和最少的队列Element数量一样。</p>
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RxSwift快速指南(三)
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<h1 id="Filter"><a href="#Filter" class="headerlink" title="Filter"></a>Filter</h1><p>Filter的操作即为过滤，是将Observable队列中不需要的Element去掉，RxSwift为我们提供了例如<code>debounce \ throttle</code>, <code>distinctUntilChanged</code>, <code>elementAt</code>, <code>filter</code>, <code>sample</code>, <code>skip</code>, <code>take</code>, <code>takeLast</code>和<code>single</code>的方法。</p>
<h2 id="debounce"><a href="#debounce" class="headerlink" title="debounce"></a>debounce</h2><p>debounce和throttle其实是一样的，队列中的元素如果和下一个元素的间隔小于了指定的时间间隔，那么这个元素将被过滤掉。</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> times = [</span><br><span class="line"> [ <span class="string">"value"</span>: <span class="number">0</span>, <span class="string">"time"</span>: <span class="number">0.1</span> ],</span><br><span class="line"> [ <span class="string">"value"</span>: <span class="number">1</span>, <span class="string">"time"</span>: <span class="number">0.4</span> ],</span><br><span class="line"> [ <span class="string">"value"</span>: <span class="number">2</span>, <span class="string">"time"</span>: <span class="number">0.6</span> ],</span><br><span class="line"> [ <span class="string">"value"</span>: <span class="number">3</span>, <span class="string">"time"</span>: <span class="number">0.8</span> ],</span><br><span class="line"> [ <span class="string">"value"</span>: <span class="number">4</span>, <span class="string">"time"</span>: <span class="number">1.0</span> ],</span><br><span class="line"> [ <span class="string">"value"</span>: <span class="number">5</span>, <span class="string">"time"</span>: <span class="number">1.4</span> ]</span><br><span class="line">];</span><br><span class="line"></span><br><span class="line">times.toObservable()</span><br><span class="line"> .flatMap { item <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">return</span> <span class="type">Observable</span>.of(item[<span class="string">"value"</span>]!)</span><br><span class="line"> .delaySubscription(<span class="type">Double</span>(item[<span class="string">"time"</span>]!), scheduler: <span class="type">MainScheduler</span>.instance)</span><br><span class="line"> }</span><br><span class="line"> .debounce(<span class="number">0.2</span>, scheduler: <span class="type">MainScheduler</span>.instance)</span><br><span class="line"> .subscribe { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br></pre></td></tr></table></figure>
<p>代码输出结果：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">Next(0.0)</span><br><span class="line">Next(4.0)</span><br><span class="line">Next(5.0)</span><br><span class="line">Completed</span><br></pre></td></tr></table></figure>
<h2 id="distinctUntilChanged"><a href="#distinctUntilChanged" class="headerlink" title="distinctUntilChanged"></a>distinctUntilChanged</h2><p>如果队列中出现相同Element，将被过滤掉。</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="type">Observable</span>.of(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">3</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>)</span><br><span class="line"> .distinctUntilChanged()</span><br><span class="line"> .subscribe { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<h2 id="filter"><a href="#filter" class="headerlink" title="filter"></a>filter</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line"><span class="type">Observable</span>.of(</span><br><span class="line"> <span class="string">"aa"</span>, <span class="string">"ab"</span>, <span class="string">"ac"</span>,</span><br><span class="line"> <span class="string">"bb"</span>, <span class="string">"aa"</span>, <span class="string">"cc"</span>,</span><br><span class="line"> <span class="string">"ca"</span>, <span class="string">"bc"</span>, <span class="string">"aa"</span>)</span><br><span class="line"> .<span class="built_in">filter</span> { $<span class="number">0</span> == <span class="string">"aa"</span> }</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">filter</span><span class="params">(predicate: <span class="params">(E)</span></span></span> <span class="keyword">throws</span> -> <span class="type">Bool</span>) -> <span class="type">Observable</span><<span class="type">E</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">Filter</span>(source: asObservable(), predicate: predicate)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>和其他FP中的filter一样，predicate返回值为布尔值，true则保留这个Element，返回false时这个Element将被过滤掉。</p>
<h2 id="sample"><a href="#sample" class="headerlink" title="sample"></a>sample</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> tap = <span class="type">Observable</span><<span class="type">NSInteger</span>>.interval(<span class="number">0.6</span>, scheduler: <span class="type">SerialDispatchQueueScheduler</span>(internalSerialQueueName: <span class="string">"tap"</span>))</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> timerSubscribe = <span class="type">Observable</span><<span class="type">NSInteger</span>>.interval(<span class="number">0.1</span>, scheduler: <span class="type">SerialDispatchQueueScheduler</span>(internalSerialQueueName: <span class="string">"timer"</span>))</span><br><span class="line"> .sample(tap)</span><br><span class="line"> .subscribeNext({ msecs -> <span class="type">Void</span> <span class="keyword">in</span></span><br><span class="line"> <span class="built_in">print</span>(<span class="string">"<span class="subst">\(msecs)</span>00ms"</span>)</span><br><span class="line"> })</span><br><span class="line"></span><br><span class="line"><span class="type">NSThread</span>.sleepForTimeInterval(<span class="number">4</span>)</span><br><span class="line">timerSubscribe.dispose()</span><br></pre></td></tr></table></figure>
<p>sample字面意思是简化，通过参数的队列来简化源队列，在官方的Example中没有找到对应例子，官方的描述也是让人想不出来这个方法适用于什么地方，直到看这个<a href="http://rx-marin.com/post/rxswift-rxcocoa-sample-split-laps-timer/" target="_blank" rel="external">这篇博客</a>才豁然开朗，需注意的是，参数队列中的元素值将被忽略。</p>
<img src="/2016/07/03/quick-guide-for-RxSwift-three/sample.png" alt="sample" title="sample">
<h2 id="其他"><a href="#其他" class="headerlink" title="其他"></a>其他</h2><p>其他方法都比较简单，通过方法名都能知道在干什么，官方的playground中也能找到对应的实例，这里就不一一阐述了。</p>
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RxSwift快速指南(二)
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<h1 id="Transform"><a href="#Transform" class="headerlink" title="Transform"></a>Transform</h1><p>接触过FP的应该都知道map，RxSwift也提供对应的方法将Element进行变形，主要的方法有<code>buffer</code>, <code>flatMap</code>, <code>flatMapFirst</code>, <code>flatMapLatest</code>, <code>map</code>, <code>scan</code>和<code>window</code>， 用的比较多的是<code>map</code>和<code>flatMap</code>。</p>
<h2 id="map"><a href="#map" class="headerlink" title="map"></a>map</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"><span class="type">Observable</span>.of(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>)</span><br><span class="line"> .<span class="built_in">map</span> { <span class="string">"<span class="subst">\($<span class="number">0</span>)</span><span class="subst">\($<span class="number">0</span>)</span>"</span> }</span><br><span class="line"> .subscribeNext { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<p>根据<code>map</code>的定义：</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">map</span><R><span class="params">(selector: E <span class="keyword">throws</span> -> R)</span></span> -> <span class="type">Observable</span><<span class="type">R</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">self</span>.asObservable().composeMap(selector)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>selector</code>这个closure负责将E转换为R，而E这里被定义为Observable.of(1, 2, 3)的Int，每个元素会被转换为String。</p>
<h2 id="flatMap"><a href="#flatMap" class="headerlink" title="flatMap"></a>flatMap</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"><span class="keyword">let</span> sequenceInt = <span class="type">Observable</span>.of(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>)</span><br><span class="line"><span class="keyword">let</span> sequenceString = <span class="type">Observable</span>.of(<span class="string">"A"</span>, <span class="string">"B"</span>, <span class="string">"C"</span>, <span class="string">"D"</span>)</span><br><span class="line"></span><br><span class="line">sequenceInt.flatMap { <span class="number">_</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">return</span> sequenceString</span><br><span class="line"> }</span><br><span class="line"> .subscribe { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<p><code>flatMap</code>的定义：</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">flatMap</span><O: ObservableConvertibleType><span class="params">(selector: <span class="params">(E)</span></span></span> <span class="keyword">throws</span> -> <span class="type">O</span>) -> <span class="type">Observable</span><<span class="type">O</span>.<span class="type">E</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">FlatMap</span>(source: asObservable(), selector: selector)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>来看看Rx官方给出的描述：</p>
<table>
<thead>
<tr>
<th>map</th>
<th>flatMap</th>
</tr>
</thead>
<tbody>
<tr>
<td>Transform the items emitted by an Observable by applying a function to each item</td>
<td>Transform the items emitted by an Observable into Observables, then flatten the emissions from those into a single Observable</td>
</tr>
</tbody>
</table>
<p><code>map</code>和<code>flatMap</code>的区别在于<code>map</code>的selector将用于Observable中的每一个Element，操作完成后，Element的数量和源Observable中的是一样的，而<code>flatMap</code>的selector的调用次数和源Element数量一致，但是由于selector的返回值为一个Observable，所以在操作完成后，得到的Elements为源Element数量*selector返回的Observable的Element数量，然后将所有Element放入一个Observable中，类似于<code>[[1, 2], [2, 3], [3, 4]]</code> -> <code>[1, 2, 2, 3, 3, 4]</code>。</p>
<img src="/2016/06/27/quick-guide-for-RxSwift-two/flatMap.png" alt="flatMap" title="flatMap">
<h2 id="flatMapLatest"><a href="#flatMapLatest" class="headerlink" title="flatMapLatest"></a>flatMapLatest</h2><p>比起<code>map</code>和<code>flatMap</code>，要稍微难理解一点：</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"></span><br><span class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>].toObservable()</span><br><span class="line"> .flatMapLatest { value <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">return</span> [<span class="string">"<span class="subst">\(value)</span>a"</span>, <span class="string">"<span class="subst">\(value)</span>b"</span>].toObservable()</span><br><span class="line"> }</span><br><span class="line"> .subscribe { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<p>根据<a href="https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/flatmaplatest.md" target="_blank" rel="external">RxJS flatMapLatest</a>这个代码期望的结果是（RxSwift和Rx系的其他语句具有相似接口，其中RxJava对应的方法是switchMap，在<a href="https://github.com/Reactive-Extensions/RxJS/blob/master/src/core/perf/operators/flatmaplatest.js" target="_blank" rel="external">RxJS Source Code</a>也能发现其实它和switchMap是一个函数）：</p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">Next(1a)</span><br><span class="line">Next(2a)</span><br><span class="line">Next(3a)</span><br><span class="line">Next(3b)</span><br><span class="line">Completed</span><br></pre></td></tr></table></figure>
<p>但是实际上得到的输出结果是：</p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">Next(1a)</span><br><span class="line">Next(1b)</span><br><span class="line">Next(2a)</span><br><span class="line">Next(2b)</span><br><span class="line">Next(3a)</span><br><span class="line">Next(3b)</span><br><span class="line">Completed</span><br></pre></td></tr></table></figure>
<p>出现这种情况的原因在github的<a href="https://github.com/ReactiveX/RxSwift/blob/master/Documentation/GettingStarted.md#creating-your-own-observable-aka-observable-sequence" target="_blank" rel="external">Get Start</a>有解释，问题出现在selector中的<code>toObservable</code>，它的实现使用了<code>Sequence</code>:</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">toObservable</span><span class="params">(scheduler: ImmediateSchedulerType? = <span class="literal">nil</span>)</span></span> -> <span class="type">Observable</span><<span class="type">Generator</span>.<span class="type">Element</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">Sequence</span>(elements: <span class="keyword">self</span>, scheduler: scheduler)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>Sequence</code>其实是一个同步队列的实现，在<code>subscribe</code>调用前会生成Next和Completed，因为无论哪种disposable被返回，生成elements的过程都不能被打断。在这种情况下，<code>flatMapLatest</code>和<code>flatMap</code>的输出结果一样。</p>
<p>期望的版本:</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"><span class="keyword">var</span> charValues: [<span class="type">Variable</span><<span class="type">Character</span>>] = [<span class="type">Variable</span>(<span class="string">"a"</span>), <span class="type">Variable</span>(<span class="string">"a"</span>), <span class="type">Variable</span>(<span class="string">"a"</span>)]</span><br><span class="line"></span><br><span class="line">[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>].toObservable()</span><br><span class="line"> .flatMapLatest { value -> <span class="type">Observable</span><<span class="type">Character</span>> <span class="keyword">in</span></span><br><span class="line"> <span class="built_in">print</span>(<span class="string">"Int value: <span class="subst">\(value)</span>"</span>)</span><br><span class="line"> <span class="keyword">return</span> charValues[value].asObservable()</span><br><span class="line"> }</span><br><span class="line"> .subscribe { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br><span class="line"></span><br><span class="line">charValues[<span class="number">2</span>].value = <span class="string">"b"</span></span><br><span class="line">charValues[<span class="number">0</span>].value = <span class="string">"c"</span> <span class="comment">// nothing happen</span></span><br><span class="line">charValues[<span class="number">1</span>].value = <span class="string">"d"</span> <span class="comment">// nothing happen</span></span><br></pre></td></tr></table></figure>
<img src="/2016/06/27/quick-guide-for-RxSwift-two/flatMapLatest.png" alt="flatMapLatest" title="flatMapLatest">
<p>和<code>flatMap</code>一样，<code>flatMapLatest</code>也会新生成一个Observable的队列，但不同的是它不会合并所有的新Observable中的Element，它会switch到最后一个Observable上（<code>switchMap</code>这个名字感觉更容易让人理解一点），先前建立的Observable将不再被监听，所以代码中charValues只有最后一个Observable还在被subscribe。</p>
<h2 id="scan"><a href="#scan" class="headerlink" title="scan"></a>scan</h2><figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> disposeBag = <span class="type">DisposeBag</span>()</span><br><span class="line"><span class="type">Observable</span>.range(start: <span class="number">1</span>, <span class="built_in">count</span>: <span class="number">3</span>)</span><br><span class="line"> .scan(<span class="number">0</span>) { $<span class="number">0</span> + $<span class="number">1</span> }</span><br><span class="line"> .subscribe { <span class="built_in">print</span>($<span class="number">0</span>) }</span><br><span class="line"> .addDisposableTo(disposeBag)</span><br></pre></td></tr></table></figure>
<p><code>scan</code>和swift的原生方法reduce很类似（区别在于scan后的Element数量和源Element数量一致，但是reduce只会返回一个Element），在Observable+Single中我们能够找到它的定义：</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">scan</span><A><span class="params">(seed: A, accumulator: <span class="params">(A, E)</span></span></span> <span class="keyword">throws</span> -> <span class="type">A</span>) -> <span class="type">Observable</span><<span class="type">A</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">Scan</span>(source: <span class="keyword">self</span>.asObservable(), seed: seed, accumulator: accumulator)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>seed</code>的scan开始的初始值，<code>accumulator</code>的第一个参数为上一次操作的返回值，第二个参数为Observable队列中的Element，然后返回处理结果。</p>
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RxSwift快速指南(一)
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<h1 id="基本概念"><a href="#基本概念" class="headerlink" title="基本概念"></a>基本概念</h1><p>每个Observable队列都仅仅是一个简单的队列，Observable比Swift中的SequenceType优秀在于它能接受异步的元素，这是RxSwift的核心概念。</p>
<h2 id="Event"><a href="#Event" class="headerlink" title="Event"></a>Event</h2><p>队列的语法： <code>Next* (Error | Completed)?</code></p>
<p>Event是一个泛型枚举，一个队列中可以有0个或者多个Next元素，当队列中出现Error和Completed元素时，队列将不再接受Next元素。</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">enum</span> <span class="title">Event</span><<span class="title">Element</span>> </span>{</span><br><span class="line"> <span class="keyword">case</span> <span class="type">Next</span>(<span class="type">Element</span>)</span><br><span class="line"> <span class="keyword">case</span> <span class="type">Error</span>(<span class="type">ErrorType</span>)</span><br><span class="line"> <span class="keyword">case</span> <span class="type">Completed</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="创建一个Observable-aka-observable-sequence"><a href="#创建一个Observable-aka-observable-sequence" class="headerlink" title="创建一个Observable(aka observable sequence)"></a>创建一个Observable(aka observable sequence)</h2><p>在Observable+Creation中，RxSwift定义了很多帮助创建Observable的方法，例如<code>create</code>, <code>empty</code>, <code>never</code>, <code>just</code>, <code>error</code>, <code>of</code>, <code>deferred</code>, <code>generate</code>, <code>repeatElement</code>和<code>using</code>, 以及对SequenceType和Array的扩展方法<code>toObservable</code>。</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">myJust</span><E><span class="params">(element: E)</span></span> -> <span class="type">Observable</span><<span class="type">E</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">Observable</span>.create { observer <span class="keyword">in</span></span><br><span class="line"> observer.on(.<span class="type">Next</span>(element))</span><br><span class="line"> observer.on(.<span class="type">Completed</span>)</span><br><span class="line"> <span class="keyword">return</span> <span class="type">NopDisposable</span>.instance</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>这里通过尾随闭包(Trailing Closures)来创建了一个Observable，create方法的定义是：</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">static</span> <span class="function"><span class="keyword">func</span> <span class="title">create</span><span class="params">(subscribe: <span class="params">(AnyObserver<E>)</span></span></span> -> <span class="type">Disposable</span>) -> <span class="type">Observable</span><<span class="type">E</span>> {</span><br><span class="line"> <span class="keyword">return</span> <span class="type">AnonymousObservable</span>(subscribe)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>这里subscribe其实是一个handler，接受一个Observer，返回一个Disposable对象，并作为AnonymousObservable的init参数传入。<code>AnyObserver<Element></code>实现了<code>ObserverType</code>协议，我们在该handler内，将<code>Event</code>通过<code>on</code>发送到队列中去，最后返回的Disposable，Disposable在Observable被<code>subscribe</code>后被返回，用作Observable的终止。</p>
<h2 id="订阅一个Observable"><a href="#订阅一个Observable" class="headerlink" title="订阅一个Observable"></a>订阅一个Observable</h2><p>在Observable被创建后，我们会得到一个Observable，它实现了<code>ObservableType</code>协议，在Observable+Extensions中，可以发现一些用于订阅的方法：<code>subscribe</code>, <code>subscribeNext</code>, <code>subscribeError</code>和<code>subscribeCompleted</code>。被创建的Observable是不会执行任何代码的，因为它只定义了Observable怎么被创建起来，只有在它被subscribe之后，队列才会真正被创建。</p>
<figure class="highlight swift"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">subscribeNext</span><span class="params">(onNext: <span class="params">(E)</span></span></span> -> <span class="type">Void</span>) -> <span class="type">Disposable</span> {</span><br><span class="line"> <span class="keyword">let</span> observer = <span class="type">AnonymousObserver</span><<span class="type">E</span>> { e <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">if</span> <span class="keyword">case</span> .<span class="type">Next</span>(<span class="keyword">let</span> value) = e {</span><br><span class="line"> onNext(value)</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">self</span>.subscribeSafe(observer)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="Observable的终止"><a href="#Observable的终止" class="headerlink" title="Observable的终止"></a>Observable的终止</h2><p>在一个subscription上调用<code>dispose</code>将终止一个被观察的队列，在create时定义的Disposable的销毁代码会被执行。</p>
<h1 id="生命周期"><a href="#生命周期" class="headerlink" title="生命周期"></a>生命周期</h1><p>在基本概念中，我们接触到了Event，Observable和Observer，他们的生命周期如图所示：</p>
<img src="/2016/06/24/quick-guide-for-RxSwift-one/RxSwift.001.png" alt="RxSwift life cycle" title="RxSwift life cycle">
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<p>本节仅介绍了RxSwift中几个重要的概念和他们是怎么协同工作的，下一节将细化Observable的transform, filter和combine。</p>
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Continuous Integration
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<h2 id="持续集成能干什么"><a href="#持续集成能干什么" class="headerlink" title="持续集成能干什么"></a>持续集成能干什么</h2><hr>
<p>在以往传统的开发中，集成往往被放在开发周期的后期–联调，这样的后果就是在开发过程中得到一个不可预知的联调阶段。联调阶段往往在传统开发模式中最为艰苦的一个阶段。</p>
<h3 id="联调中主要问题"><a href="#联调中主要问题" class="headerlink" title="联调中主要问题"></a>联调中主要问题</h3><ul>
<li>在开发初期没有考虑好的架构、接口等问题。</li>
<li>由于单独模块开发时可能使用不相同的运行环境，集成后环境不统一，造成的程序运行不稳当。</li>
</ul>
<p>持续集成的出现，旨意解决在联调中出现问题，持续集成，将联调进行拆分，分成步骤很小的集成，分散到整个开发过程中，而不是把集成放到软件开发的末期。</p>
<h3 id="持续集成的好处"><a href="#持续集成的好处" class="headerlink" title="持续集成的好处"></a>持续集成的好处</h3><ul>
<li>由于将集成放到了每个开发周期，一旦有集成的问题，能够及时的发现，并进行修复。</li>
<li>解决频繁部署的问题，可以及时的将测试版本交由客户，从而及时得到客户的反馈，保证开发的系统确实的用户所需要的。</li>
<li>由于每次集成后构建，都可以得到一个可运行的系统，从另一方面考虑，降低了客户的资金风险。</li>
<li>持续集成过程中使用到一些自动化构建测试大大降低了工作量，虽然初期需要花比较成的时间搭建持续集成环境，但是长远考虑，这是有利的。</li>
<li>持续集成，能够将项目的当前状况，及时反馈给每一个开发者，从而降低了开发过程中的交流成本。</li>
</ul>
<hr>
<h2 id="只维护一个源码仓库"><a href="#只维护一个源码仓库" class="headerlink" title="只维护一个源码仓库"></a>只维护一个源码仓库</h2><p>源代码管理系统现在多用分布式的git，需要注意是：需将所有文件都放进源代码管理系统，除了代码外，还需要将相关测试脚本，配置文件，数据库Schema，安装脚本，第三方库，甚至IDE的配置文件。以确保一个原则：<strong>任何人都可以找到一台干净的机器，做一次取出（checkout）动作，然后对系统执行一次完整的构建。</strong></p>
<p>使用同一个源码仓库的优势：</p>
<ul>
<li>使得每个协同工作的worker，都能快速的获得同样的、最新的代码，保证了<strong>集成的时效性</strong>，并能<strong>快速找出集成中出现的问题</strong>。</li>
<li>在开发过程中，如果需要增加worker，一次checkout就能让其马上立即得到可行的工作环境。</li>
</ul>
<hr>
<h2 id="使用持续集成构建"><a href="#使用持续集成构建" class="headerlink" title="使用持续集成构建"></a>使用持续集成构建</h2><h3 id="构建流程"><a href="#构建流程" class="headerlink" title="构建流程"></a>构建流程</h3><p><img src="http://www.infoq.com/resource/articles/ci-theory-practice/zh/resources/image1.png" alt="持续集成构建"></p>
<ul>
<li>更新<ul>
<li>每次在编辑代码前，需要从源码仓库中更新的代码，保证本地代码和代码仓库中的代码一致，为最新代码。</li>
</ul>
</li>
<li>编辑代码<ul>
<li>编辑代码完成尽量小的一个feature和对应的测试代码。</li>
</ul>
</li>
<li>本地构建<ul>
<li>对修改的代码进行自测试。</li>
</ul>
</li>
<li>更新<ul>
<li>再次从源码仓库中更新代码，因为在完成feature的同时，可能有其他人提交有新的代码。</li>
</ul>
</li>
<li>本地构建<ul>
<li>再次本地构建，保证新从仓库中检出的代码，和自己开发的feature没有集成错误。</li>
</ul>
</li>
<li>提交<ul>
<li>将代码提交到代码仓库。</li>
</ul>
</li>
<li>提交构建<ul>
<li>该步骤一般可又CI系统在代码提交后自动进行构建。</li>
</ul>
</li>
</ul>
<p>在构建中，一般分为这7个步骤。在一个步骤中，一般又可划分为多个小步骤。例如编辑代码步骤，在完成一个feature的时候，一般可将这个feature进行再拆分，每完成一个更小的feature后，使用git commit到local repository，保证代码在出现问题的时候，能够方便的进行git reset。</p>
<p>需要注意的步骤是step 6，setp 1~5因为都是local repository的操作，在做错后可以回滚，step 6会将本地代码push到remote repository中。所以，<strong>步骤6的前置本地构建，必须通过，通过所有测试，才能执行step 6.</strong></p>
<hr>
<h2 id="自动化build、自动化测试、自动化部署"><a href="#自动化build、自动化测试、自动化部署" class="headerlink" title="自动化build、自动化测试、自动化部署"></a>自动化build、自动化测试、自动化部署</h2><p>为项目选用合适的自动化build的工具是非常有必要的。</p>
<ul>
<li>可以把源码转变成一个可运行的系统这个过程简单化。</li>
<li>智能的build工具，可以检查源码之间的依赖项和修改项，选择性的编译，降低大型build的时间。</li>
<li>build脚本允许在不同的情况中build不同的target。</li>
</ul>
<p>自动化工具，可选用ant，maven，gradle等，IDE也会有对应的命令行工具，如MSBuild，xcodebuild等，当然还有一些工具如shell，PowerShell等，也会在自动化build中使用</p>
<p>开发者在开发时，可以使用IDE作为build工具，但是主build还是需要自动化的build工具，以保证他可以在开发服务器上运行。</p>
<ul>
<li>自动化测试，极限编程（Extreme Programming）和驱动测试开发（TDD）待续。。。</li>
<li>自动化部署待续。。。</li>
</ul>
<hr>
<h2 id="反馈和沟通"><a href="#反馈和沟通" class="headerlink" title="反馈和沟通"></a>反馈和沟通</h2><ul>
<li>及时向mainline提交代码，并在CI Master上重新构建</li>
<li>保持快速build</li>
<li>让每个人都能轻易获得最新的可执行文件</li>
<li>每个人都能看到进度</li>
</ul>
<p>以上这些步骤，都是为了一个目的：沟通。<br>沟通的角色有开发环节中的各个角色，以及和客户直接，每次DEV在开发完一个feature后，提交代码，在CI Master上进行重新构建，构建的结果将显示的公共的显示器上，以便于每个worker都能及时的查看到结果和进度。<br>保持快速build以及让每个人都能轻易获得最新的可执行文件，为了就是能够尽快从其他worker和客户那里获得反馈，保证了沟通的畅通性。</p>
<h3 id="分阶段构建（Staged-Build）"><a href="#分阶段构建（Staged-Build）" class="headerlink" title="分阶段构建（Staged Build）"></a>分阶段构建（Staged Build）</h3><ul>
<li>分离关注度不同的验证阶段。</li>
<li>构建流程可视化。</li>
<li>通过分阶段并发构建来缩短反馈周期。</li>
</ul>
<p>构建的过程一般会耗费很长时间，可将构建工作分为多个job，并行进行构建。这点在Jenkins中可轻松完成。</p>
<hr>
<h2 id="其他技巧"><a href="#其他技巧" class="headerlink" title="其他技巧"></a>其他技巧</h2><ul>
<li>在模拟生产环境中进行测试</li>
</ul>
<hr>
<h4 id="参考文献"><a href="#参考文献" class="headerlink" title="参考文献"></a>参考文献</h4><ul>
<li><a href="http://article.yeeyan.org/view/2251/94882" target="_blank" rel="external">持续集成（第二版）Martin Fowler</a></li>
<li><a href="http://www.infoq.com/cn/articles/ci-theory-practice" target="_blank" rel="external">持续集成理论和实践的新进展 肖鹏</a></li>
</ul>
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