dart中的“常量创建的参数必须是常量表达式”是什么？ [英] What is the `Arguments of a constant creation must be constant expressions` in dart?

问题描述

我不知道为什么Dart编译器在代码中向我显示错误。这到底是什么意思？谢谢。

I don't know why the dart compiler shows me an error in my code. What is that actually means? Thanks.

来源：

          const SliverAppBar(
        pinned: true,
        expandedHeight: 300.0, // TODO: check out later
        flexibleSpace: FlexibleSpaceBar(
            title: new Column(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                Text('_SliverAppBar'),
                Text('subtitle'),
              ],
            ),
            background: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text('Info'),
              ],
            )),

推荐答案

我已评论了导致该问题的原始答案。但这是为什么：

I have commented the original answer that lead to that problem. But here is why:

正如@aziza所指出的，您已将 SliverAppBar 实例化为 const 关键字。因此，所有属性都应使用 const 实例化。

As @aziza pointed, you have instantiated your SliverAppBar with the const keyword. Therefore, all properties should be instantiated with const.

在您的情况下，只需更改 new Column 到 const Column 可以解决该问题，但是dart 2可以推断出它将如何实例化该类。只需省略 new 和 const 关键字，然后让dart完成工作即可。

In your case, just changing from new Column to const Column would solve the problem, but, dart 2 can infer how it will instantiate the class. Just omit the new and const keywords, and let dart do the work.

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