Dart语法基础系列五《String 源码API详解》

abstract class String implements Comparable, Pattern

| 接口名称 | 用途 |

| — | — |

| Comparable | 对比接口 |

| Pattern | 搜索匹配接口 |

String 基于Comparable、Pattern具备其功能

String源码接口

---

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fromCharCodes

charCodes 16位以内：

/// Allocates a new string containing the specified [charCode].

///

/// If the [charCode] can be represented by a single UTF-16 code unit, the new

/// string contains a single code unit. Otherwise, the [length] is 2 and

/// the code units form a surrogate pair. See documentation for

/// [fromCharCodes].

///

/// Creating a [String] with one half of a surrogate pair is allowed.

external factory String.fromCharCode(int charCode);

使用：

main() {

print(String.fromCharCode(97)); // a

}

charCodes 超过16位

源码函数：

/// If [start] and [end] are provided, only the values of [charCodes]

/// at positions from start to, but not including, end, are used.

/// The start and end values must satisfy

/// 0 <= start <= end <= charCodes.length.

external factory String.fromCharCodes(Iterable charCodes,

[int start = 0, int? end]);

var clef = String.fromCharCodes([0x1D11E]);

clef.codeUnitAt(0); // 0xD834

clef.codeUnitAt(1); // 0xDD1E

fromEnvironment

作用: flutter 启动的时候可以设置环境变量，可以通过fromEnvironment获取环境变量的内容。

API源码：

external const factory String.fromEnvironment(String name,

{String defaultValue = “”});

例子：

const String.fromEnvironment(“defaultFloo”, defaultValue: “no floo”)

可以通过bool.hasEnvironment判断是否存在

const maybeDeclared = bool.hasEnvironment(“maybeDeclared”)

? String.fromEnvironment(“maybeDeclared”)

null;

length

API:

int get length;

例子：

‘Dart’.length; // 4

‘Dart’.runes.length; // 4

var clef = ‘\u{1D11E}’;

clef.length; // 2

clef.runes.length; // 1

== 等号操作符

检查每个code units 是否相等，不比较Unicode的等价性。

API源码：

bool operator ==(Object other);

compareTo

作用： 比较字符串是否相，返回整型，0相等，-1不相等。

API源码：

int compareTo(String other);

例子：

var a = ‘a’;

var b = ‘a’;

var c = ‘c’;

print(a.compareTo(b)); //0

print(a.compareTo©); //-1

endsWith

作用: 判断是否以XX字符串结尾

API源码：

bool endsWith(String other);

例子：

‘Dart’.endsWith(‘t’); // true

startsWith

作用： 判断