Swift基础语法（一）
发布时间：2020-12-14 07:16:44 所属栏目：百科 来源：网络整理
导读：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
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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
7.字典 常见的字典使用如下： http://blog.csdn.net/qq441571205/article/details/45606323
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