swift详解之十八------------ScrollView

ScrollView

注：本小节详细介绍scrollView的用法

UIScrollView是一个能够滚动的视图控件，可以用来展示大量的内容，并且可以通过滚动查看所有的内容

UIScrollView的用法，将需要展示的内容添加到UIScrollView中

设置UIScrollView的contentView属性，告诉UIScrollView所有内容的尺寸

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">let scroll = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIScrollView</span>();
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.backgroundColor</span> = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIColor</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.grayColor</span>()
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">30</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">150</span>)  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置scrollview的大小</span>
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.contentSize</span> = CGSizeMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">400</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">150</span>)   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//内容大小</span>
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.pagingEnabled</span> = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>                 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//是否支持分页</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//scroll.contentOffset = CGPointMake(0, -10)</span>
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.contentInset</span> = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIEdgeInsets</span>(top: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>,left: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>,bottom: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>,right: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//内边距</span>

let imageView =  <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImageView</span>(image: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImage</span>(named: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dog1"</span>))
imageView<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">130</span>)
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.addSubview</span>(imageView)

let imageView1 =  <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImageView</span>(image: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImage</span>(named: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dog2"</span>))
imageView1<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>+<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">130</span>)
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.addSubview</span>(imageView1)

let imageView2 =  <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImageView</span>(image: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImage</span>(named: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dog3"</span>))
imageView2<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>*<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>+<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">130</span>)
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.addSubview</span>(imageView2)

let imageView3 =  <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImageView</span>(image: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIImage</span>(named: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dog4"</span>))
imageView3<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>*<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>+<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">130</span>)
scroll<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.addSubview</span>(imageView3)

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.view</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.addSubview</span>(scroll)</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul>

这里我创建了一个scrollview 并设置的一些属性（都有注释） ， 然后 添加了四个小狗的图片 。 效果就是横向拖动可轮换显示四张图



滑动可轮换
下面介绍一个可缩放的示例

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">
let scrollview = UIScrollView()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span>, viewWidth-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">300</span>)
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.backgroundColor</span> = UIColor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.purpleColor</span>()
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.contentInset</span> = UIEdgeInsets(top: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, left:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, bottom: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, right: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)

imageView4 =  UIImageView(image: UIImage(named: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"pic1"</span>))
imageView4!<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.frame</span> = CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>,viewWidth-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">280</span>)
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addSubview</span>(imageView4!)
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.contentSize</span>=CGSizeMake( viewWidth-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">300</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.maximumZoomScale</span>=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; //设置最大伸缩比例</span>
scrollview<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.minimumZoomScale</span>=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.5</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; //设置最小伸缩比例</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

同样是设置一些基本属性 ， 然后设置伸缩比例

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">    <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ViewController</span>: <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">UIViewController</span> , <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">UIScrollViewDelegate</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

让我们的controller实现UIScrollViewDelegate这个协议

<code class="hljs oxygene has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"> scrollview.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">delegate</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

把scrollview的代理 设成当前对象

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//告诉scrollview要缩放的是哪个子控件</span>
func viewForZoomingInScrollView(scrollView: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIScrollView</span>) -> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIView</span>? {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> imageView4
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

然后实现这个方法，告诉scrollview要缩放的是哪个子控件

运行看看 确实可以缩放了。。
下面看看UIScrollViewDelegate 中的一些其他的事件

<code class="hljs scss has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">func <span class="hljs-function" style="box-sizing: border-box;">scrollViewDidScroll(scrollView: UIScrollView)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"只要滚动了就会触发哦。"</span>)</span>
}

func <span class="hljs-function" style="box-sizing: border-box;">scrollViewWillBeginDragging(scrollView: UIScrollView)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"开始拖拽视图"</span>)</span>
}

func <span class="hljs-function" style="box-sizing: border-box;">scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"结束滚动"</span>)</span>
}

func <span class="hljs-function" style="box-sizing: border-box;">scrollViewWillBeginDecelerating(scrollView: UIScrollView)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"将开始降速时"</span>)</span>
}

func <span class="hljs-function" style="box-sizing: border-box;">scrollViewDidEndDecelerating(scrollView: UIScrollView)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"减速停止了时执行，手触摸时执行执行"</span>)</span>
}

func <span class="hljs-function" style="box-sizing: border-box;">scrollViewDidEndScrollingAnimation(scrollView: UIScrollView)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"滚动动画停止时执行,代码改变时触发,也就是setContentOffset改变时"</span>)</span>
}

func <span class="hljs-function" style="box-sizing: border-box;">scrollViewDidEndZooming(scrollView: UIScrollView, withView view: UIView?, atScale scale: CGFloat)</span> {
<span class="hljs-function" style="box-sizing: border-box;">print(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"完成放大缩小时调用"</span>)</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul>

这里面都清楚的记载了什么时候执行。。很清楚，大家可以试试
最后再附上这些实例的源码（本实例在xcode 7 beta上实现） ：scrollview
都提交了发现还少点什么 ， 原来少了这个图 。（本图来源于网络）



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