# Dart語言基礎 - 變量聲明: ``` <pre class="calibre14">``` var name<span class="token">=</span><span class="token4">"張三"</span><span class="token2">;</span> 不指定類型 函數類使用 dynamic name<span class="token">=</span><span class="token4">"11"</span><span class="token2">;</span> 不確定具體類型時候用 String name <span class="token">=</span> <span class="token4">'bob'</span><span class="token2">;</span> 指定具體類型 var name<span class="token2">;</span> 沒有賦值情況下<span class="token2">,</span>所有類型都是<span class="token5">null</span> 變量作用域在<span class="token2">{</span><span class="token2">}</span>中確定<span class="token2">,</span>層級越深作用域越小<span class="token2">,</span>函數外的作用域很大 final name<span class="token">=</span><span class="token4">"11"</span><span class="token2">;</span> 只能賦值一次<span class="token2">,</span>內容不會改變 const pi<span class="token">=</span><span class="token3">3.14</span><span class="token2">;</span> 編譯時候的常量 ``` ``` - 數據類型,基本類型有數字,字符,布爾 ``` <pre class="calibre14">``` int a<span class="token">=</span><span class="token3">1</span><span class="token2">;</span> 整型 double b<span class="token">=</span><span class="token3">1.01</span> 雙精度浮點數 num c<span class="token">=</span><span class="token3">1.1</span> 同時支持整型和浮點 方法或屬性 isEven 是否偶數 isOdd 是否奇數 字符串可以是單引號或雙引號<span class="token2">,</span>變量可以$name替換<span class="token2">,</span>表達式$<span class="token2">{</span><span class="token2">}</span>替換<span class="token2">,</span>拼接字符串用<span class="token">+</span><span class="token2">,</span>多行使用<span class="token4">''</span>'或<span class="token4">""</span>" String name<span class="token">=</span> <span class="token4">'Hi ${name.toUpperCase()}'</span><span class="token2">;</span> String name<span class="token">=</span><span class="token4">''</span>'你好 世界<span class="token4">''</span>'<span class="token2">;</span> 屬性或方法 length 長度 isEmpty是否為空 布爾 只有<span class="token3">true</span> 和<span class="token3">false</span><span class="token2">,</span>只有值為<span class="token3">true</span>才是真其余都是<span class="token3">false</span><span class="token2">;</span> List類型<span class="token2">,</span>有序集合其它語言的數組 var a<span class="token">=</span><span class="token2">[</span><span class="token4">"a"</span><span class="token2">,</span><span class="token4">"b"</span><span class="token2">]</span><span class="token2">;</span> 或者 var a<span class="token">=</span><span class="token5">new</span> <span class="token1">List</span><span class="token2">(</span><span class="token2">)</span><span class="token2">;</span>a<span class="token2">.</span><span class="token1">add</span><span class="token2">(</span><span class="token4">"a"</span><span class="token2">)</span><span class="token2">;</span> Set類型<span class="token2">,</span>無序集合 var gameSet <span class="token">=</span> <span class="token2">{</span><span class="token4">'Halo'</span><span class="token2">,</span> <span class="token4">'God of War'</span><span class="token2">}</span><span class="token2">;</span> var a<span class="token">=</span><span class="token5">new</span> <span class="token1">Set</span><span class="token2">(</span><span class="token2">)</span><span class="token2">;</span> Map類型 var gameMap <span class="token">=</span> <span class="token2">{</span><span class="token4">'microsoft'</span><span class="token2">:</span> <span class="token4">'Halo'</span><span class="token2">,</span> <span class="token4">'sony'</span> <span class="token2">:</span><span class="token4">'God of War'</span><span class="token2">}</span><span class="token2">;</span> gameMap<span class="token2">[</span><span class="token4">"sony"</span><span class="token2">]</span><span class="token">=</span><span class="token4">"1"</span><span class="token2">;</span> ``` ``` - 運算符 ``` <pre class="calibre14">``` a is String 是否是字符串<span class="token2">,</span>判斷類型 a is<span class="token">!</span> String 不屬于某個類型 name as String 類型轉換 var message <span class="token">=</span> input<span class="token">?</span><span class="token">?</span> <span class="token4">'Hello'</span><span class="token2">;</span> 判斷input是否<span class="token5">null</span><span class="token2">,</span>不是直接返回input<span class="token2">,</span>否則hello person<span class="token2">.</span><span class="token2">.</span>name <span class="token">=</span> <span class="token4">'bob'</span><span class="token2">.</span><span class="token2">.</span>age <span class="token">=</span> <span class="token3">28</span><span class="token2">;</span> 連續操作<span class="token2">.</span><span class="token2">.</span> var message<span class="token2">;</span> message <span class="token">?</span><span class="token">?</span><span class="token">=</span> <span class="token4">'Hello'</span><span class="token2">;</span> 賦值判斷是否為<span class="token5">null</span><span class="token2">,</span>然后賦值 ``` ``` - 定義函數 ``` <pre class="calibre14">``` String <span class="token1">bobSay</span><span class="token2">(</span>String words<span class="token2">)</span> <span class="token2">{</span> <span class="token5">return</span> <span class="token4">'bob say $words'</span><span class="token2">;</span> <span class="token2">}</span> String <span class="token1">bobSay2</span><span class="token2">(</span>String words<span class="token2">)</span> <span class="token">=</span><span class="token">></span> <span class="token4">'bob say $words'</span><span class="token2">;</span> <span class="token6">//簡寫</span> String <span class="token1">fn</span><span class="token2">(</span>String a<span class="token2">,</span><span class="token2">[</span>String a<span class="token">=</span><span class="token3">1</span><span class="token2">]</span><span class="token2">)</span><span class="token2">{</span><span class="token2">}</span><span class="token6">//調用 fn(1,2),第二個可選</span> String <span class="token1">fn</span><span class="token2">(</span><span class="token2">{</span>String a<span class="token2">,</span>int b<span class="token">=</span><span class="token3">1</span><span class="token2">}</span><span class="token2">)</span><span class="token2">{</span><span class="token2">}</span> <span class="token6">//調用 fn(a:"aa",b:3)</span> ``` ``` - 類 ``` <pre class="calibre14">``` class <span class="token1">A</span><span class="token2">{</span> static int a<span class="token">=</span><span class="token3">1</span><span class="token2">;</span> static <span class="token1">fn</span><span class="token2">(</span>string w<span class="token2">)</span><span class="token2">{</span><span class="token2">}</span> <span class="token1">a</span><span class="token2">(</span><span class="token2">)</span><span class="token2">{</span> <span class="token2">}</span>和類同名函數為構造函數初始化變量<span class="token2">,</span>不能有<span class="token5">return</span> factory <span class="token1">a</span><span class="token2">(</span><span class="token2">)</span><span class="token2">{</span> <span class="token5">return</span> <span class="token2">}</span> factory修飾的工廠構造函數必須有<span class="token5">return</span> <span class="token2">}</span> ``` ``` 庫 ``` <pre class="calibre16">``` <span class="token6">// 三種形式的庫導入</span> import dart<span class="token2">:</span>io<span class="token2">;</span> 自帶標準庫 import <span class="token4">'../base.dart'</span><span class="token2">;</span> import <span class="token4">'package:test/test.dart'</span><span class="token2">;</span> ``` ```