飞镖之后的构造函数 [英] Colon after Constructor in dart

问题描述

此代码来自flutter画廊，我正在尝试理解和改编它。我会知道此语法的含义：

This code is from flutter gallery and i'm trying to understanding and adapting it. I would know what this syntax means:

class DemoItem<T> {
  DemoItem({
    this.valueName,
    this.hintName,
    this.valueSurname,
    this.hintSurname,
    this.builder,
    this.valueToString

  }) : textController = new TextEditingController(text: valueToString(valueName));

特别是，我会知道在构造函数之后的冒号是什么，以及是否存在

Especially i would know what means the colon after the constructor and if there is a way to define another TextEditingController, in addition to the one already defined.

推荐答案

之后的部分是一种定义另一个TextEditingController的方法。 ：称为初始化列表。这是一个，分隔的表达式列表，可以访问构造函数参数并可以分配给实例字段，甚至 final 实例字段，这很方便初始化带有计算值的最终字段。

The part after : is called "initializer list. It is a ,-separated list of expressions that can access constructor parameters and can assign to instance fields, even final instance fields. This is handy to initialize final fields with calculated values.

初始化程序列表也可用于调用其他构造函数，例如：...，super（'foo'）。

The initializer list is also used to call other constructors like : ..., super('foo').

自Dart 1.24版开始list还支持 assert（...），它很方便检查参数值。

Since about Dart version 1.24 the initializer list also supports assert(...) which is handy to check parameter values.

初始化列表可以请从 this 中读取，因为超级构造函数需要在访问 this 有效之前完成，但它可以分配给 this.xxx 。

The initializer list can't read from this because the super constructors need to be completed before access to this is valid, but it can assign to this.xxx.

根据user693336的注释中的说明指出：

Pointing out as mentioned in the comments by user693336:

这也意味着初始化列表在构造函数体之前执行。同样，所有超类的初始化列表都在执行任何构造器主体之前执行。

This also means the initializer list is executed before the constructor body. Also the initializer lists of all superclasses are executed before any of the contructor bodies are executed.

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