flutter语法中三点的含义 [英] Meaning of Triple Dots [...] in Flutter Syntax

问题描述

有人可以澄清一下Flutter中"..."的含义和用法吗?

Can someone please clarify what is the meaning and usage of "..." in Flutter?

我想了解Flutter语法中使用的三点".经过一番阅读后，我发现我要找的词是传播".

I wanted to learn about "triple dots" used in Flutter syntax. After some reading I found out that the word I was looking for was "spreading".

Widget _build() {
  List<Widget> children = [
    Text("first child"),
    Text("second child"),
    Text("third child"),
  ];

  return Column(
    children: <Widget>[
      ...children,
      Text("fourth child"),
    ],
  );
}

如果我在children,之前没有...，它将给出错误The element type 'List<Widget>' can't be assigned to the list type 'Widget'.

If I didn't have the ... right before the children, it will give an error The element type 'List<Widget>' can't be assigned to the list type 'Widget'.

我只是认为有人应该发布有关此问题的信息. flutter语法中的"..."是什么?是什么意思?

I just thought that someone should post a question about it. What is "..." in flutter syntax? What does it mean?

推荐答案

Dart 2.3引入了散布运算符(...)和可识别null的散布运算符(...?)，它们提供了一种插入多个简明格式的简洁方法元素添加到集合中.

Dart 2.3 introduced the spread operator (...) and the null-aware spread operator (...?), which provide a concise way to insert multiple elements into a collection.

例如，您可以使用传播运算符(...)将列表的所有元素插入另一个列表:

For example, you can use the spread operator (...) to insert all the elements of a list into another list:

var list = [1, 2, 3];
var list2 = [0, ...list];
assert(list2.length == 4);

如果扩展运算符右边的表达式可能为null，则可以使用可识别null的扩展运算符(...?)来避免出现异常:

If the expression to the right of the spread operator might be null, you can avoid exceptions by using a null-aware spread operator (...?):

var list;
var list2 = [0, ...?list];
assert(list2.length == 1);

有关使用传播运算符的更多详细信息和示例，请参见

For more details and examples of using the spread operator, see the spread operator proposal.

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