寫Flutter之前先弄懂Dart
關鍵字(Keywords)
常數(Constant)
- final
final String language = "Dart";final name = "Bond";
2.const (編譯常量compile-time constants)
和final的差異 → const在編譯時就載入，final在所屬的class初始化時才載入
//定義常數
const num = 15;//產生常數指定給變數
var foo = const [];
final bar = const [];
const baz = const [];
變數(Variable)
var number = 1;
var message = 'text';沒有初始值時，預設為null。
型別
- number：num, int , double
型別轉換example:
// String -> int
var one = int.parse('1');// String -> double
var onePointOne = double.parse('1.1');// int -> String
String oneAsString = 1.toString();// double -> String
String piAsString = 3.14159.toStringAsFixed(2);
常用操作：
a. 運算符+-*/ , ~/取整數, ％取餘數
b. isNaN是否非數字,iSEven是否為偶數, isOdd是否為奇數
2.String：UTF-16
var s1 = 'Single quotes work well for string literals.'; //單引號var s2 = "Double quotes work just as well."; //雙引號var s3 = 'Dart has $s1 and $s2';var s4 = 'That deserves all caps. ' + '${s1.toUpperCase()} is very handy!'; //插值表達式var s4_text = 'That deserves all caps. ' + 'STRING INTERPOLATION is very handy!';String s5 = '''Hello,
Dart.'''; //三引號，多行字符串String s6 = "Hello,\n Dart."; //換行符var r1 = s1 * 5; //重複n次var r2 = (s1 == s2); //判斷是否相等var r3 = s1[1]; //取字元var r4 = s1.length; //長度var 45 = s1.isEmpty; //是否為空
3.boolean
bool a = true;bool b = false;
4.list (array)
var list1 = new List();var list2 = [1,2,3,"Dart",true]; //元素可以是不同型別list[0] = "Hello";var list3 = const [1,2,3]; //不可變的listlist2.add("Hi"); //從後方添加list2.insert(1,"iOS"); //從index添加list1.clear(); //清空list2.sublist(1); //子陣列list2.forEach(print); //遍歷list.asMap(); //list轉map
5.map
var searchTerms = new Map();var nobleGases = new Map<int, String>();var language = {"first":"dart","second":"swift",1:true};print(language["first"]);print(language.keys);print(language.values);language.forEach(function1);
void function1(key,value) {
print("key=$key,value=$value");
}
6.dynamic (泛型)
var a;
a = 10;
a = "dart";dynamic b = 20;var list = new List<dynamic>();
7.runes (for expressing Unicode characters in a string)
8.symbol
運算符(operator)
1.算術運算符
int a = 10;
int b = 20;print(a ~/ b); //取整數
print(a % b); //取餘數print(a++);
print(++a);
2.關係運算符
int a = 10;
int b = 20;print(a == b);
print(a != b);
print(a > b);
print(a <= b);String c = "123";
String d = "321";print(c == d); //判斷字符串相等
3.邏輯運算符
bool a = true;
bool b = false;print(!a);
print(a && b);
print(a || b);
4.賦值運算符
int a = 10;
int b;b ??= 10; //如果變數沒有值，才給值a += 2;
a -= b;
a ~/= b;
a %= b;
5.條件表達式、三元語法糖
int genter = 0;
String str = (gender == 0 ? "M" : "F");String a;
String b = "Dart";
String c = a ?? b; //a為空時就使用b
控制流程
1.if else 判斷
int score = 90;if (score > 90) {
print(""優秀);
} else (score => 60) {
print("良好");
} else {
print("不及格");
}
2.for迴圈
var list = [1,2,3,4];for (var index = 0,index < list.length;index ++) {
print(list[index]);
}for (var item in list) {
print(item);
}
3.while迴圈
var count = 0;while(count < 5) {
print(count++);
}do {
print(count--);
} while (count > 0 && count < 5);
4.break和continue
var list = [1,2,3,4,5];for (var item, in list) {
if(item == 2) {
continue; //繼續下一個迴圈
} if (item == 4) {
break; //終止所在迴圈
}
print(item);
}
5.switch case
String language = "Dart";switch(language) {
case A:
print("a");
break;
case "Dart":
print("language is Dart");
break;
case "Swift":
print("language is Swift");
continue A; //跳轉到自定義標記
case "Java":
print("language is Java");
break;
default:
break;
}
函式(Function)
1.定義函式
void main() {
func1([1,2,3]);
}String func1(List args) {
print(args);
return "123";
}printName(name) {
print("name = $name"); //回傳值和參數類型都可以省略
//沒有回傳值時，默認為null
}//箭頭省略僅適用一個表達式
var result = getName(name) => return "name = $name";
2.可選參數
void main() {
printPerson("Dart");
printPerson("Dart", age: 10); printPerson2("Dart");
printPerson2("Dart",10);
}printPerson(String name, {int age, String gender}) {
// age和gender為可選參數，可以不傳
}printPerson2(String name ,[int age, String gender]) {
//age和gender為可選參數，不使用變數名稱，依照順序傳值
//可選參數需定義於固定參數後面
}
3.默認參數值
void main() {
printPerson("Dart");
printPerson("Dart", age: 10, gender: "M");
}printPerson(String name, {int age = 5, String gender = "F"}) {
}
4.方法對象
void main() {
Function func = printName; //方法對象可以是變數或參數
var list = [1,2,3];
listTimes(list, times);
}void printName() {
print("Name");
}List listTimes(List list,String times(str)) {
for(var index = 0;index< list.length;index++) {
list[index] = times(list[index]);
}
return list;
}String times(str) {
return str*3;
}
5.匿名方法
void main() {
var func = (name) {
print("hello,$name");
}
func("Dart"); var list = [1,2,3];
var result = listTimes(list,(name) { return name * 3 });
}List listTimes(List list,String times(str)) {
for(var index = 0;index< list.length;index++) {
list[index] = times(list[index]);
}
return list;
}
6.閉包
void main() {
var func = a();
func(); //0
func(); //1
}a() {
int count = 0; //持有局部變量的狀態
return () {
print(count++) ;
};
}
參考：
