blocks|key|5761023|text|这个问题是在我升级Flutter之后发生的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5761024|我通过清理和再次升级项目依赖解决了这个问题。|offset|length|style|BOLD|5761025|在项目的根目录下运行以下命令：|5761026|flutter+clean
flutter+packages+pub+upgrade
flutter+pub+run+build_runner+build|code-block|syntax|javascript|5761027|另外，正如其他人所说，请确保您在pubspec.yaml中的sdk版本与flutter+sdk版本兼容。|CODE|5761028|entityMap^0|0|3|B|0|0|0|G|C|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@$D|V|E|W|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|Y|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|Z|8|@$D|10|E|11|F|Q]]|9|@]|A|$]]|$1|R|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|S|$]]

This problem was occured for me after upgrading the Flutter. 
I solved it by cleaning and upgrading the project dependencies again. 
Run the below commands in the root directory of your project:
<pre><code>flutter clean
flutter packages pub upgrade
flutter pub run build_runner build
</code></pre>
Also as others said, please make sure your sdk version in the <code>pubspec.yaml</code> is compatible with your flutter sdk version.

blocks|key|1736006|text|为了使零安全起作用，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1736007|environment:
+++sdk:+">=2.12.0+<3.0.0"|code-block|syntax|javascript|1736008|至少应该是这个版本。然后运行flutter+clean和flutter+pub+get就可以了。|offset|length|style|CODE|1736009|entityMap^0|0|0|E|D|S|F|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

For null safety to work,
<pre><code>environment:
 sdk: &quot;&gt;=2.12.0 &lt;3.0.0&quot;
</code></pre>
should be this version at least.
then run <code>flutter clean</code>
and <code>flutter pub get</code> it will work.

blocks|key|5760999|text|试一试|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5761000|flutter+clean|code-block|syntax|javascript|5761001|这对我很有效！|5761002|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Try
<pre><code>flutter clean
</code></pre>
This is worked for me!

blocks|key|5760990|text|取决于你正在做什么，有时它就像改变你的pubspec.yaml文件中的环境来更新低端一样简单，即改变一个低端，比如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5760991|environment:
sdk:+">=2.0.0+<3.0.0"|code-block|syntax|javascript|5760992|至|5760993|environment:
sdk:+">=2.6.0+<3.0.0"|5760994|或|5760995|environment:
sdk:+">=2.7.0+<3.0.0"|5760996|这对导致这个错误的各种情况都有效(在最新版本的flutter和dart中使用扩展语法也会导致这个错误)，但我不需要旧的环境。|5760997|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Depending on what you're doing, sometimes it's as simple as changing the environment in your pubspec.yaml file to update the lower end, ie change a lower end like

<pre><code>environment:
sdk: "&gt;=2.0.0 &lt;3.0.0"
</code></pre>

to

<pre><code>environment:
sdk: "&gt;=2.6.0 &lt;3.0.0"
</code></pre>

or

<pre><code>environment:
sdk: "&gt;=2.7.0 &lt;3.0.0"
</code></pre>

This has worked for the various things that cause this error (using spread syntax in latest version of flutter and dart will also cause this), but I don't need the older environments.

blocks|key|4343928|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4343929|对我来说，一个简单的修复方法是确保analysis_options.yaml位于根文件夹中。在我的例子中，它在lib文件夹中，直到我将文件移到与pubspec.yaml相同的文件夹中，所有实验特性都不起作用。其他可能发生的事情包括使实验功能不再需要的更新，因此除了验证文件位置之外，在颤动主通道上更新到最新版本可能也很有用。但是，我无法使用此选项运行命令行。|blockquote|4343930|4343931|4343932|4343933|Dart+Reference+|unordered-list-item|offset|length|4343934|Example+of+Analysis+Options+File|4343935|4343936|entityMap|0|LINK|mutability|MUTABLE|url|https://dart.dev/guides/language/analysis-options#the-analysis-options-file|1|https://github.com/flutter/flutter/blob/master/analysis_options.yaml^0|0|0|0|0|0|0|E|0|0|0|W|1|0|0^^$0|@$1|2|3|-4|4|5|6|Y|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|Z|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|10|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|11|7|@]|8|@]|9|$]]|$1|F|3|-4|4|5|6|12|7|@]|8|@]|9|$]]|$1|G|3|H|4|I|6|13|7|@]|8|@$J|14|K|15|1|16]]|9|$]]|$1|L|3|M|4|I|6|17|7|@]|8|@$J|18|K|19|1|1A]]|9|$]]|$1|N|3|-4|4|5|6|1B|7|@]|8|@]|9|$]]|$1|O|3|-4|4|5|6|1C|7|@]|8|@]|9|$]]]|P|$Q|$4|R|S|T|9|$U|V]]|W|$4|R|S|T|9|$U|X]]]]

<blockquote>
 A simple fix for me was to ensure that the analysis_options.yaml is in
 the root folder. In my case, it was in the lib folder and none of the
 experimental features worked until I moved the file to the same folder
 as pubspec.yaml. Other things that can happen include updates that
 make the experimental feature no longer required so updating to the
 latest version on the flutter master channel may be useful in addition
 to verifying the file location. Haven't been able to get the command line 
 running with this option, however. 
</blockquote>

<ul>
<li><a href="https://dart.dev/guides/language/analysis-options#the-analysis-options-file" rel="nofollow noreferrer">Dart Reference</a> </li>
<li><a href="https://github.com/flutter/flutter/blob/master/analysis_options.yaml" rel="nofollow noreferrer">Example of Analysis Options File</a></li>
</ul>

I am playing around with non-nullable types and added this to my <code>analysis_options.yaml</code>:

<pre><code>analyzer:
 enable-experiment:
 - non-nullable
</code></pre>

I have a code-generator that is utilising the nullability extension. Visual Code is fine with my code.

Now, I try to run:

<pre><code>flutter packages pub run build_runner watch 
</code></pre>

I get this error message:

<pre><code>[SEVERE] Failed to snapshot build script .dart_tool/build/entrypoint/build.dart.
This is likely caused by a misconfigured builder definition.
[SEVERE] xyz.dart:95:7: Error: This requires the 'non-nullable' experiment to be enabled.Try enabling this experiment by adding it to the command line when compiling and running.
</code></pre>

How can I pass <code>--enable-experiment:non-nullable</code> to <code>flutter packages pub run</code>?

The same happens if I run:

<pre><code>flutter build ios
</code></pre>

I get the error message:

<pre><code> lib/main.dart:61:26: Error: This requires the 'non-nullable' experiment to be enabled.

 Try enabling this experiment by adding it to the command line when compiling and running.
</code></pre>

So, same question: How can I pass <code>--enable-experiment:non-nullable</code> to <code>flutter build</code>?

Error: This requires the 'non-nullable' experiment to be enabled

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在使用不可为空的类型，并将其添加到我的analysis_options.yaml中analyzer:  enable-experiment:    - non-nullable我有一个代码生成器，它利用了可空性扩展。可视化代码对我的代码来说很好。现在，我试着运行：flutter packages pub run build_runner watch 我收到这个错误消息：[SEVERE] Fai

问错误:这需要启用“不可为空”实验
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