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Dart核心库常见方法学习

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Dart 学习记录

这几篇关于Dart的文章，只是在看官网教程的时候敲一遍巩固记忆而写的

Dart:core

每个文件都会默认引入这个包，包括numbers,collections,strings等等

print

打印，默认会调用打印的对象的 toString 方法

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print(anObject)
const name = 'Jsonz'
print('I\'m $name');

Numbers

parse

解析把字符串转为数字

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assert(int.parse('42') == 42);
assert(int.parse('0x42') == 66);
assert(double.parse('0.50') == 0.5);
assert(num.parse('42') is int);
assert(num.parse('0x42') is int);
assert(num.parse('0.50') is double);
assert(int.parse('42', radix: 16) == 66);

toString

将数字转为字符串

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// Convert an int to a string.
assert(42.toString() == '42');

// Convert a double to a string.
assert(123.456.toString() == '123.456');

// Specify the number of digits after the decimal.
assert(123.456.toStringAsFixed(2) == '123.46');

// Specify the number of significant figures.
assert(123.456.toStringAsPrecision(2) == '1.2e+2');
assert(double.parse('1.2e+2') == 120.0);

String

search inside a string

字符串的查找搜索

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var str = 'Never odd or even';
assert(str.contains('odd'));
assert(str.startsWith('Never'));
assert(str.endsWith('even'));
assert(str.indexOf('odd') == 6);

Extracting data from a string

从字符串提取数据

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var str = 'Never odd or even';
assert(str.substring(6, 9) == 'odd');

var parts = str.split(' ');
assert(parts.length == 4);
assert(parts[0] == 'Never');

assert(str[0] == 'N');
for (var char in 'hello'.split('')) {
  print(char);
}

var codeUnitList = str.codeUnits.toList();
assert(codeUnitList[0] == 78);

converting to uppercase or lowercase

切换大小写

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var str = 'Never odd or even';
assert(str.toUpperCase() == 'NEVER ODD OR EVEN');
assert(str.toLowerCase() == 'never odd or even');

trimming && empty

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assert('   hello '.trim() == 'hello');
assert(''.isEmpty);
assert(' '.isNotEmpty);

replace

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var greetingTemplate = 'Hello, Name!';
var greeting = greetingTemplate.replaceAll(RegExp('Name'), 'Bob');
print(greeting); // Hello, Bob!
assert(greeting != greetingTemplate);

building a string

在调用toString之前不会生成新的字符串对象。

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var sb = StringBuffer();

sb
  ..write('use a stringBuffer for ')
  ..writeAll(['efficient', 'string', 'creation'], '')
  ..write('.');

var fullString = sb.toString();
assert(fullString ==  'Use a StringBuffer for efficient string creation.');

正则

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final numbers = RegExp(r'\d+');

const allCharacters = 'llamas live fifteen to twenty years';
const someDigits = 'llamas live 15 to 20 years';

assert(!allCharacters.contains(numbers));
assert(someDigits.contains(numbers));

final exedOut = someDigits.replaceAll(numbers, 'XX');
assert(exedOut == 'llamas live XX to XX years');

assert(numbers.hasMatch(someDigits));

for (var match in numbers.allMatches(someDigits)) {
  print(match.group(0));
}

Collections

List、Set、Map

List

普通数组

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// 基础操作
listBase() {
  // Use a List constructor.
  var vegetables = List();
  assert(vegetables.length == 0);

  // simply use a list literal.
  var fruits = ['apples', 'oranges'];
  // add to a list.
  fruits.add('kiwis');
  // add multiple items to a list.
  fruits.addAll(['grapes', 'bananas']);

  // Get the list length.
  assert(fruits.length == 5);

  // remove a single item.
  var appleIndex = fruits.indexOf('apples');
  fruits.removeAt(appleIndex);
  assert(fruits.length == 4);

  // remove all elements from a list
  fruits.clear();
  assert(fruits.length == 0);

  assert(fruits[0] == 'apples');
  assert(fruits.indexOf('apples') == 0);
}

// sort 方法
listSort() {
  var fruits = ['bananas', 'apples', 'oranges'];
  // Sort a list.
  fruits.sort((a, b) => a.compareTo(b));
  assert(fruits[0] == 'apples');
}

// list type 
listType() {
  var fruits = List<String>();
  fruits.add('apples');
  var fruit = fruits[0];
  assert(fruit is String);
}

Set

去重类数组

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// Set base
setBase() {
  var ingredients = Set();
  ingredients.addAll(['gold', 'titanium', 'xenon']);
  assert(ingredients.length == 3);

  ingredients.add('gold');
  assert(ingredients.length == 3);

  ingredients.remove('gold');
  assert(ingredients.length == 2);
}

// 是否包含
setContains() {
  var ingredients= Set();
  ingredients.addAll(['gold', 'titanium', 'xenon']);

  // check whether an item is in the set.
  assert(ingredients.contains('titanium'));

  // check whether all the items are in the set.
  assert(ingredients.containsAll(['titanium', 'xenon']));
}

// 交集
setIntersection() {
  var ingredients= Set();
  ingredients.addAll(['gold', 'titanium', 'xenon']);

  // create the intersection of thw sets.
  var nobleGases = Set.from(['xenon', 'argon']);
  var intersection = ingredients.intersection(nobleGases);

  assert(intersection.length == 1);
  assert(intersection.contains('xenon'));
}

关于Set的更多方法

Maps

js对象

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// 基础创建
mapBase() {
  var hawaiianBeaches = {
    'Oahu': ['Waikiki', 'Kailua', 'Waimanalo'],
    'Big Island': ['Wailea bay', 'Pololu Beach'],
    'Kauai': ['Hanalei', 'Poipu'],
  };

  var searchTerms = Map();

  var nobleGases = Map<int, String>(); 
}

// 移除
mapRemove() {
  var nobleGases = {
    54: 'xenon',
  };
  assert(nobleGases[54] == 'xenon');
  assert(nobleGases.containsKey(54));

  nobleGases.remove(54)  ;
  assert(!nobleGases.containsKey(54));
}

// keys && values
mapKeyValue() {
  var hawaiianBeaches = {
    'Oahu': ['Waikiki', 'Kailua', 'Waimanalo'],
    'Big Island': ['Wailea bay', 'Pololu Beach'],
    'Kauai': ['Hanalei', 'Poipu'],
  };

  // keys
  var keys = hawaiianBeaches.keys;
  assert(keys.length == 3);
  assert(Set.from(keys).contains('Oahu'));

  // values
  var values = hawaiianBeaches.values;
  assert(values.length == 3);
  assert(values.any((v)=> v.contains('Waikiki')));

  // check a keys
  assert(hawaiianBeaches.containsKey('Oahu'));
  assert(!hawaiianBeaches.containsKey('Florida'));

  // putIfAbsent 当且仅当没有该Key赋值，才会执行该函数
  var teamAssignments = {};
  teamAssignments.putIfAbsent('Catcher', ()=> 'test');
  assert(teamAssignments['Catcher'] != null);
}

更多关于Maps的API

通用(Map,Set,List)的方法

Iterable(迭代器)方法指Set和List，因为他们是继承Iterable class
Collections指 Set、List和Map.

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commonSetList() {

  //Iterables 指的是List和Set，因为都是继承该类实现的
  // Collections 指的是List,Set,Map

  var coffees = [];
  var teas = ['green', 'black', 'chamomile', 'earl grey'];
  var teasSet = {'green', 'black'};
  var teasMap = {
    'tea1': 'green',
    'tea2': 'black',
  };

  // Iterables: isEmpty isNotEmpty
  assert(coffees.isEmpty);
  assert(teas.isNotEmpty);
  assert(teasSet.isNotEmpty);

  // Collections: forEach
  teas.forEach((tea)=> {
    print('I drink $tea')
  });
  teasMap.forEach((teaKey, teaValue)=> {
    print('$teaKey, $teaValue')
  });

  // Iterbables: map. map使用的是惰性模式，即在上一个返回之前，不会执行下一个函数
  var loudTeas = teas.map((tea)=> tea.toUpperCase());
  loudTeas.forEach(print);

  // 如果想要立即执行，可以使用 toList 或 toSet
  var loudTeas2 = teas.map((tea)=> tea.toUpperCase()).toList();
  print(loudTeas2);

  // where any every 和js一样的功能，分别是查找所有符合的，有任意符合返回true，所有符合返回true
  bool isDecaffeinated(String teaName)=> teaName == 'chamomile';
  var decaffeinatedTeas = teas.where(isDecaffeinated);
  print(decaffeinatedTeas);
  assert(teas.any(isDecaffeinated));
  assert(!teas.every(isDecaffeinated));
}

URI

URI主要提供一些解码和编码url的功能

解码与编码

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encodeAndDecode() {
  var uri = 'http://example.org/api?foo=some message';
  var encoded = Uri.encodeFull(uri);
  assert(encoded == 'http://example.org/api?foo=some%20message');

  var decode = Uri.decodeFull(encoded);
  assert(uri == decode);

  var encodeComponent = Uri.encodeComponent(uri);
  assert(encodeComponent == 'http%3A%2F%2Fexample.org%2Fapi%3Ffoo%3Dsome%20message');
  var decoded = Uri.decodeComponent(encodeComponent);
  assert(uri == decoded);
}

解析与构建

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parseAndBuild() {
  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 == 'frage');
  assert(uri.origin == 'http://example.org:8080');

  var buildUri = Uri(
    scheme: 'http',
    host: 'example.org',
    path: '/foo/bar',
    fragment: 'frag'
  );
  assert(buildUri.toString() == 'http://example.org/foo/bar#frag');
}

Dates and times

时间日期相关

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date() {
  var now = DateTime.now();

  // create a now DateTime with the local time zone.
  var y2k = DateTime(2000); 

  // 指定月份和日期
  y2k = DateTime(2000, 1, 2);

  // specify the date as a UTC time.
  y2k = DateTime.utc(2000);

  // 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');

  // 返回从1970到目标的毫秒数
  y2k = DateTime.utc(2000);
  assert(y2k.millisecondsSinceEpoch == 946684800000);

  var unixEpoch = DateTime.utc(1970);
  assert(unixEpoch.millisecondsSinceEpoch == 0);
}

// 时间操作方法
dateOptions() {
  var y2k = DateTime.utc(2000);
  print(Duration(days: 366));
  var y2001 = y2k.add(Duration(days: 366));
  assert(y2001.year == 2001);

  // subtract 30 days
  var december2000 = y2001.subtract(Duration(days: 30));
  assert(december2000.year == 2000);
  assert(december2000.month == 12);

  // Calculate the difference between two dates.
  // Returns a Duration object.  
  var duration = y2001.difference(y2k);
  assert(duration.inDays == 366);
}

更多DateTime API
更多Duration API

未完待续