变量
var name = 'Bob';
dynamic name = 'Bob';
String name = 'Bob';
final name = 'Bob'; // A final variable can be set only once
final String nickname = 'Bobby';
const bar = 1000000; // compile-time constants
const double atm = 1.01325 * bar;
Number
int x = 1;
int hex = 0xDEADBEEF;
var one = int.parse('1');//1
var onePointOne = double.parse('1.1');//1.1
String oneAsString = 1.toString();//'1'
String piAsString = 3.14159.toStringAsFixed(2);//'3.14'
String
var s2 = 'The + operator ' + 'works, as well.';
var content = 'world';
var hello = 'Hello ${content}';//Hello world
List
var list = [1, 2, 3];
list.length == 3;
list[1] = 1;
var names = List<String>();
names.addAll(['Seth', 'Kathy', 'Lars']);
names.add('Jack');
var constantList = const [1, 2, 3];
// constantList[1] = 1; // Uncommenting this causes an error.
var teas = ['green', 'black', 'chamomile', 'earl grey'];
teas.forEach((tea) => print('I drink $tea'));
var loudTeas =
teas.map((tea) => tea.toUpperCase()).toList();
// Chamomile is not caffeinated.
bool isDecaffeinated(String teaName) =>
teaName == 'chamomile';
// Use where() to find only the items that return true
// from the provided function.
var decaffeinatedTeas =
teas.where((tea) => isDecaffeinated(tea));
// or teas.where(isDecaffeinated)
// Use any() to check whether at least one item in the
// collection satisfies a condition.
assert(teas.any(isDecaffeinated));
// Use every() to check whether all the items in a
// collection satisfy a condition.
assert(!teas.every(isDecaffeinated));
Map
var gifts = {
// Key: Value
'first': 'partridge',
'second': 'turtledoves',
'fifth': 'golden rings'
};
var nobleGases = {
2: 'helium',
10: 'neon',
18: 'argon',
};
var gifts = Map();
gifts['first'] = 'partridge';
gifts['second'] = 'turtledoves';
gifts['fifth'] = 'golden rings';
var nobleGases = Map();
nobleGases[2] = 'helium';
nobleGases[10] = 'neon';
nobleGases[18] = 'argon';
var gifts = {'first': 'partridge'};
gifts['fourth'] = 'calling birds'; // Add a key-value pair
gifts.length == 2;//length
final constantMap = const {
2: 'helium',
10: 'neon',
18: 'argon',
};
// constantMap[2] = 'Helium'; // Uncommenting this causes an error.
var nobleGases = {54: 'xenon'};
// Retrieve a value with a key.
assert(nobleGases[54] == 'xenon');
// Check whether a map contains a key.
assert(nobleGases.containsKey(54));
// Remove a key and its value.
nobleGases.remove(54);
assert(!nobleGases.containsKey(54));
var hawaiianBeaches = {
'Oahu': ['Waikiki', 'Kailua', 'Waimanalo'],
'Big Island': ['Wailea Bay', 'Pololu Beach'],
'Kauai': ['Hanalei', 'Poipu']
};
// Get all the keys as an unordered collection
// (an Iterable).
var keys = hawaiianBeaches.keys;
assert(keys.length == 3);
assert(Set.from(keys).contains('Oahu'));
// Get all the values as an unordered collection
// (an Iterable of Lists).
var values = hawaiianBeaches.values;
assert(values.length == 3);
assert(values.any((v) => v.contains('Waikiki')));
assert(hawaiianBeaches.containsKey('Oahu'));
hawaiianBeaches.forEach((k, v) {
print('I want to visit $k and swim at $v');
// I want to visit Oahu and swim at
// [Waikiki, Kailua, Waimanalo], etc.
});
函数
bool isNoble(int atomicNumber) {
return _nobleGases[atomicNumber] != null;
}
isNoble(atomicNumber) {//省略返回值声明
return _nobleGases[atomicNumber] != null;
}
bool isNoble(int atomicNumber) => _nobleGases[atomicNumber] != null;//短语法
void enableFlags({bool bold = false, bool hidden = false}) {...}
([[Type] param1[, …]]) { //匿名函数
codeBlock;
};
类型测试
if (emp is Person) {
// Type check
emp.firstName = 'Bob';
}
(emp as Person).firstName = 'Bob';//类型转换，但如果emp不是Person类型就会抛出异常
瀑布语法
querySelector('#confirm') // Get an object.
..text = 'Confirm' // Use its members.
..classes.add('important')
..onClick.listen((e) => window.alert('Confirmed!'));
//相当于
var button = querySelector('#confirm');
button.text = 'Confirm';
button.classes.add('important');
button.onClick.listen((e) => window.alert('Confirmed!'));
控制语句
var callbacks = [];
for (var i = 0; i < 2; i++) {
callbacks.add(() => print(i));
}
callbacks.forEach((c) => c());
var collection = [0, 1, 2];
for (var x in collection) {
print(x); // 0 1 2
}
遍历
class Process {
// Represents a process...
}
class ProcessIterator implements Iterator<Process> {
@override
Process get current => ...
@override
bool moveNext() => ...
}
// A mythical class that lets you iterate through all
// processes. Extends a subclass of [Iterable].
class Processes extends IterableBase<Process> {
@override
final Iterator<Process> iterator = ProcessIterator();
}
void main() {
// Iterable objects can be used with for-in.
for (var process in Processes()) {
// Do something with the process.
}
}
异常
assert(number < 100);//Make sure the value is less than 100
//定义异常：
class FooException implements Exception {
final String msg;
const FooException([this.msg]);
@override
String toString() => msg ?? 'FooException';
}
throw FormatException('Expected at least 1 section');
try {
breedMoreLlamas();
} on OutOfLlamasException {
buyMoreLlamas();
}
try {
breedMoreLlamas();
} on OutOfLlamasException {
// A specific exception
buyMoreLlamas();
} on Exception catch (e) {
// Anything else that is an exception
print('Unknown exception: $e');
} catch (e) {
// No specified type, handles all
print('Something really unknown: $e');
}
try {
breedMoreLlamas();
} catch (e) {
print('Error: $e'); // Handle the exception first.
} finally {
cleanLlamaStalls(); // Then clean up.
}
URI
var uri = 'http://example.org/api?foo=some message';
var encoded = Uri.encodeComponent(uri);//'http%3A%2F%2Fexample.org%2Fapi%3Ffoo%3Dsome%20message'
var decoded = Uri.decodeComponent(encoded);
var uri =
Uri.parse('http://example.org:8080/foo/bar#frag');
assert(uri.scheme == 'http');
assert(uri.host == 'example.org');
assert(uri.path == '/foo/bar');
assert(uri.fragment == 'frag');
assert(uri.origin == 'http://example.org:8080');
ar uri = Uri(
scheme: 'http',
host: 'example.org',
path: '/foo/bar',
fragment: 'frag');
assert(
uri.toString() == 'http://example.org/foo/bar#frag');
类
abstract class Point {
num x=4;
num y;
Point(this.x,this.y);
Point.zero(){
x= 0;
y = 0;
}
void toStr();
}
class Dot extends Point {
num radius;
static const initialCapacity = 16;//类属性
Dot.zero() : super.zero() {
radius = 5;
}
num get left => x - radius;
set centerX(num value) => x = value;
void toStr(){
print('(${x},${y},${radius})');
}
static printClassProp(){
print('static $initialCapacity');
}
}
枚举
enum Color { red, green, blue }
var aColor = Color.blue;
范型
abstract class Cache<T> {
T getByKey(String key);
void setByKey(String key, T value);
}
var names = <String>['Seth', 'Kathy', 'Lars'];
class Foo<T extends SomeBaseClass> {
// Implementation goes here...
String toString() => "Instance of 'Foo<$T>'";
}
var someBaseClassFoo = Foo<SomeBaseClass>();
class Extender extends SomeBaseClass {...}
var extenderFoo = Foo<Extender>();
var foo = Foo();
T first<T>(List<T> ts) {
// Do some initial work or error checking, then...
T tmp = ts[0];
// Do some additional checking or processing...
return tmp;
}
引用库
import 'dart:html';
//The package: scheme specifies libraries provided by a package manager such as the pub tool
import 'package:test/test.dart';
import 'package:lib1/lib1.dart';
import 'package:lib2/lib2.dart' as lib2;
// Uses Element from lib1.
Element element1 = Element();
// Uses Element from lib2.
lib2.Element element2 = lib2.Element();
// Import only foo.
import 'package:lib1/lib1.dart' show foo;
// Import all names EXCEPT foo.
import 'package:lib2/lib2.dart' hide foo;
import 'package:greetings/hello.dart' deferred as hello;//懒加载式声明
Future greet() async {
await hello.loadLibrary();//加载库
hello.printGreeting();//调用库
}
异步处理
Future checkVersion() async {
var version = await lookUpVersion();
// Do something with version
}
Future<String> lookUpVersion() async => '1.0.0';//Declaring async functions
typedef
typedef Compare = int Function(Object a, Object b);
日期时间
DateTime.now()//当前时间
var y2k = DateTime(2000); // January 1, 2000
// Specify the month and day.
y2k = DateTime(2000, 1, 2); // January 2, 2000
// Specify the date as a UTC time.
y2k = DateTime.utc(2000); // 1/1/2000, UTC
// Specify a date and time in ms since the Unix epoch.
y2k = DateTime.fromMillisecondsSinceEpoch(946684800000,
isUtc: true);
// Parse an ISO 8601 date.
y2k = DateTime.parse('2000-01-01T00:00:00Z');
var y2001 = y2k.add(const Duration(days: 366));
assert(y2001.year == 2001);
var duration = y2001.difference(y2k);
assert(duration.inDays == 366); // y2k was a leap year.
定时器
import 'dart:async';
Timer timer = new Timer(Duration(milliseconds: 100), update);
void update() {
print('update');
timer = new Timer(Duration(milliseconds: 100), update);
}
