Swift基础语法（一）

1.常量&变量

使用var关键字定义变量，可以修改

使用let关键字定义常量，不可修改

提示：在Swift开发中，通常先定义常量let，只有必须要修改的时候，才定义成var，这样会更安全。

2.类型转换

Swift是一个对类型要求及其严格的语言，任何数据类型之间，都不能隐式转换。如果要在不同的类型之间进行计算，必须转换格式

解决方案一：强制转换

提示：Swift在上面定义i,j常量的时候自动推断了类型，Swift中默认的整数格式是Int（long 64位），默认的小数格式是Double（而OC中默认的小数格式是CGFloat）。

解决方案二：定义的时候指明类型

3.分支语句

在C语言中，if有一个特点，“非零即真”。但是在Swift中，没有这个概念，在分支语句中，必须准确地指明条件的真假。

Swift中的条件语句有两个特点：

1>条件不需要括号

2>必须要有 {}

4. 循环

循环的主要用法有以下四种：

5.字符串

Swift中默认的字符串类型为String，是一个结构体，所以它的效率更高

<ol class="linenums list-paddingleft-2" style="margin:0px; width:803.6875px; padding-left:30px; color:rgb(30,52,123)"><li class="L0" style="clear:both; color:rgb(190,190,197); line-height:18px; padding-left:12px"><code class="language-cpp" style="margin:0px; padding:0px; border:none; font-family:Consolas,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="kwd" style="color:#1e347b;">import</span><span class="pln" style="color:#48484c;"> </span><span class="typ" style="color:teal;">UIKit</span></code></li><li class="L1" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"></code>
</li><li class="L2" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">var str </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"Hello World"</span></code></li><li class="L3" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"></code>
</li><li class="L4" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 快速遍历字符串</span></code></li><li class="L5" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="kwd" style="color:#1e347b;">for</span><span class="pln" style="color:#48484c;"> c in str </span><span class="pun" style="color:#93a1a1;">{</span></code></li><li class="L6" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">  println</span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">c</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L7" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pun" style="color:#93a1a1;">}</span></code></li><li class="L8" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"></code>
</li><li class="L9" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 字符串之间拼接</span></code></li><li class="L0" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">var str1 </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> str </span><span class="pun" style="color:#93a1a1;">+</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"，你好"</span></code></li><li class="L1" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">let i </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="lit" style="color:#195f91;">100</span></code></li><li class="L3" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">let view </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="typ" style="color:teal;">UIView</span><span class="pun" style="color:#93a1a1;">()</span></code></li><li class="L4" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">view</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">backgroundColor </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="typ" style="color:teal;">UIColor</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">redColor</span><span class="pun" style="color:#93a1a1;">()</span></code></li><li class="L5" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"></code>
</li><li class="L6" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 变量拼接进字符串</span></code></li><li class="L7" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">println</span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">str1 </span><span class="pun" style="color:#93a1a1;">+</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"(i) aaa (view.backgroundColor)"</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L8" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">//字符串格式化</span></code></li><li class="L0" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">let str2 </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="typ" style="color:teal;">String</span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">format</span><span class="pun" style="color:#93a1a1;">:</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"%02d:%02d:%02d"</span><span class="pun" style="color:#93a1a1;">,</span><span class="pln" style="color:#48484c;"> arguments</span><span class="pun" style="color:#93a1a1;">:</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">[</span><span class="lit" style="color:#195f91;">1</span><span class="pun" style="color:#93a1a1;">,</span><span class="pln" style="color:#48484c;"> </span><span class="lit" style="color:#195f91;">5</span><span class="pun" style="color:#93a1a1;">,</span><span class="pln" style="color:#48484c;"> </span><span class="lit" style="color:#195f91;">10</span><span class="pun" style="color:#93a1a1;">])</span></code></li><li class="L1" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 在Swift中，如果字符串要结合range一起使用，建议先转成NSString</span></code></li><li class="L3" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 因为 swift 的字符串和range一起使用很蛋疼</span></code></li><li class="L4" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">let myString</span><span class="pun" style="color:#93a1a1;">:</span><span class="pln" style="color:#48484c;"> </span><span class="typ" style="color:teal;">NSString</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"hello"</span></code></li><li class="L5" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">myString</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">substringWithRange</span><span class="pun" style="color:#93a1a1;">(</span><span class="typ" style="color:teal;">NSMakeRange</span><span class="pun" style="color:#93a1a1;">(</span><span class="lit" style="color:#195f91;">1</span><span class="pun" style="color:#93a1a1;">,</span><span class="pln" style="color:#48484c;"> </span><span class="lit" style="color:#195f91;">4</span><span class="pun" style="color:#93a1a1;">))</span></code></li></ol>

字符串的快速遍历

字符串拼接

6.数组

添加元素</span></code></li><li class="L7" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">array4</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">append</span><span class="pun" style="color:#93a1a1;">(</span><span class="str" style="color:#dd1144;">"hello"</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L8" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">array4</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">append</span><span class="pun" style="color:#93a1a1;">(</span><span class="str" style="color:#dd1144;">"world"</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L9" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 数组容量</span></code></li><li class="L1" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">println</span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">array4</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">capacity</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L2" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// keepCapacity表示是否保持容量，如果为true当再次追加元素的时候，会在原有容量的基础上乘以2,如果是false，则是当前容量*2</span></code></li><li class="L4" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">array4</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">removeAll</span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">keepCapacity</span><span class="pun" style="color:#93a1a1;">:</span><span class="pln" style="color:#48484c;"> </span><span class="kwd" style="color:#1e347b;">true</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L5" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="kwd" style="color:#1e347b;">for</span><span class="pln" style="color:#48484c;"> i in </span><span class="lit" style="color:#195f91;">0.</span><span class="pun" style="color:#93a1a1;">..</span><span class="lit" style="color:#195f91;">5</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">{</span></code></li><li class="L7" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">  array4</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">append</span><span class="pun" style="color:#93a1a1;">(</span><span class="str" style="color:#dd1144;">"(i)"</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L8" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">  println</span><span class="pun" style="color:#93a1a1;">(</span><span class="str" style="color:#dd1144;">"(array4): (array4.capacity)"</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L9" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pun" style="color:#93a1a1;">}</span></code></li></ol>

7.字典

常见的字典使用如下：

内容</span></code></li><li class="L4" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">dict1</span><span class="pun" style="color:#93a1a1;">[</span><span class="str" style="color:#dd1144;">"name"</span><span class="pun" style="color:#93a1a1;">]</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"laolin"</span></code></li><li class="L5" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">dict1</span><span class="pun" style="color:#93a1a1;">[</span><span class="str" style="color:#dd1144;">"age"</span><span class="pun" style="color:#93a1a1;">]</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="lit" style="color:#195f91;">88</span></code></li><li class="L6" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">//再次设置会覆盖</span></code></li><li class="L8" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">dict1</span><span class="pun" style="color:#93a1a1;">[</span><span class="str" style="color:#dd1144;">"name"</span><span class="pun" style="color:#93a1a1;">]</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"abc"</span></code></li><li class="L9" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">// 删除</span></code></li><li class="L1" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">dict1</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">removeValueForKey</span><span class="pun" style="color:#93a1a1;">(</span><span class="str" style="color:#dd1144;">"age"</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L2" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="com" style="color:#93a1a1;">//合并字典</span></code></li><li class="L4" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">var dict2 </span><span class="pun" style="color:#93a1a1;">=</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">[</span><span class="str" style="color:#dd1144;">"title"</span><span class="pun" style="color:#93a1a1;">:</span><span class="pln" style="color:#48484c;"> </span><span class="str" style="color:#dd1144;">"boss"</span><span class="pun" style="color:#93a1a1;">]</span></code></li><li class="L5" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="kwd" style="color:#1e347b;">for</span><span class="pln" style="color:#48484c;"> </span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">k</span><span class="pun" style="color:#93a1a1;">,</span><span class="pln" style="color:#48484c;"> v</span><span class="pun" style="color:#93a1a1;">)</span><span class="pln" style="color:#48484c;"> in dict2 </span><span class="pun" style="color:#93a1a1;">{</span></code></li><li class="L6" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pln" style="color:#48484c;">  dict1</span><span class="pun" style="color:#93a1a1;">.</span><span class="pln" style="color:#48484c;">updateValue</span><span class="pun" style="color:#93a1a1;">(</span><span class="pln" style="color:#48484c;">v</span><span class="pun" style="color:#93a1a1;">,</span><span class="pln" style="color:#48484c;"> forKey</span><span class="pun" style="color:#93a1a1;">:</span><span class="pln" style="color:#48484c;"> k</span><span class="pun" style="color:#93a1a1;">)</span></code></li><li class="L7" style="clear:both; color:rgb(190,monospace; word-wrap:break-word; max-width:100%; background-color:transparent"><span class="pun" style="color:#93a1a1;">}</span></code></li></ol>

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Swift基础语法（一）

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