记录在Flutter开发中遇到的一系列问题、分析过程及解决方法。
1. 给现有Flutter应用添加Web支持，运行报bad import错
错误信息
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| $ flutter run -d chrome
Launching lib/main.dart on Chrome in debug mode...
Unable to find modules for some sources, this is usually the result of either a
bad import, a missing dependency in a package (or possibly a dev_dependency
needs to move to a real dependency), or a build failure (if importing a
generated file).
Please check the following imports:
`import 'generated_plugin_registrant.dart';` from flutter_jzcf|lib/utils/encrypt_web_entrypoint.dart at 5:1
Failed after 2.3s
Building application for the web... 12.2s
Failed to build application for the Web.
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原因是app中存在多个main()函数，注释掉其他不必要的测试main()函数，只保留一个即可。
2. 设置CocoaPods报ruby: bad interpreter: No such file or directory
错误信息
在配置iOS环境时，安装CocoaPods后，设置报如下错误
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| $ pod setup
-bash: /usr/local/bin/pod: /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby: bad interpreter: No such file or directory
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确认pod路径
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| $ which pod
/usr/local/bin/pod
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确认cocoapods安装状态
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| $ gem list --local |grep coco
cocoapods (1.8.4)
cocoapods-core (1.8.4)
cocoapods-deintegrate (1.0.4)
cocoapods-downloader (1.3.0)
cocoapods-plugins (1.0.0)
cocoapods-search (1.0.0)
cocoapods-stats (1.1.0)
cocoapods-trunk (1.4.1)
cocoapods-try (1.1.0)
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说明cocoapods有安装，再确认一下cocoapods 信息
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| $ gem info cocoapods
*** LOCAL GEMS ***
cocoapods (1.8.4)
Authors: Eloy Duran, Fabio Pelosin, Kyle Fuller, Samuel Giddins
Homepage: https://github.com/CocoaPods/CocoaPods
License: MIT
Installed at: /usr/local/lib/ruby/gems/2.6.0
The Cocoa library package manager.
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初步发现问题：目前path上获取的pod是在/usr/local/bin/pod的，而我们安装的在/usr/local/lib/ruby/gems/2.6.0，说明并非我们安装的版本，回想起之前处理升级到Catalina的兼容问题时（见修复升级Catalina后Jekyll本地预览启动失败）修改过ruby后，所有安装的gems均已经在此目录下，在其中的bin中存放了各个包的可执行入口，包含了这里的pod：
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| $ ls /usr/local/lib/ruby/gems/2.6.0/bin
bundle github-pages nokogiri sandbox-pod xcodeproj
bundler httpclient pod sass
commonmarker jekyll rake sass-convert
fuzzy_match kramdown rougify scss
gemoji listen safe_yaml update_rubygems
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问题解决
修改Paths
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| $ echo 'export PATH="/usr/local/lib/ruby/gems/2.6.0/bin:$PATH"' >> ~/.bash_profile
$ source ~/.bash_profile
# 再次执行pod相关命令则不会再报错了
$ pod --version
1.8.4
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异常情况
关于Scaffold AppBar的automaticallyImplyLeading参数，默认为true，根据doc注释：
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| /// Controls whether we should try to imply the leading widget if null.
/// If true and [leading] is null, automatically try to deduce what the leading
/// widget should be. If false and [leading] is null, leading space is given to [title].
/// If leading widget is not null, this parameter has no effect.
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automaticallyImplyLeading=true，同时leading Widget未设置，系统应该会自动根据需要显示返回键等leading Widget默认实现。
但有时却不会显示？
只有Scaffold作为根Widget时，AppBar automaticallyImplyLeading=true，才能根据存在上级路由时自动显示返回键
问题解决
两种方式：
- 将Scaffold作为根Widget
- 如果布局需要无法作为根Widget，则显式指定leading Widget，如返回键：
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| Scaffold(
appBar: AppBar(
//显式指定返回键
leading: BackButton(
onPressed: () => Navigator.pop<bool>(context, false),
),
),
))
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4. Waiting for another flutter command to release the startup lock…
问题现象
AndroidStudio的时候顶部的模拟器一直是loading状态，即使已经打开了模拟器。运行flutter doctor 提示：
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| $ flutter doctor
Waiting for another flutter command to release the startup lock...
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问题解决
从提示中得知，因为有上一条命令未结束而锁定了，如果确认无其他在执行的命令，那可以到Flutter安装目录/bin/cache/，删除lockfile文件，再执行Flutter命令就正常了
5. asset在debug、profile下可以读取，但到了release就无法读取，报Unable to load asset的问题
背景：flutter的buildtype默认只有debug profile release三个，而我是add-to-app的，而原宿主app是有debug alpha beta release4个buildtype，add-to-app后，就在宿主app上定义了debug profile alpha beta release共5个
遇到的问题
我在宿主app上debug profile release三个buildtype下asset读取无异常，但flutter module上没有的alpha beta上时就所有asset都无法读取。
Flutter版本信息如下：
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| $ flutter doctor -v
[✓] Flutter (Channel beta, v1.17.0-3.2.pre, on Mac OS X 10.15.3 19D76, locale
zh-Hans-CN)
• Flutter version 1.17.0-3.2.pre at /Users/peter/Data/flutter
• Framework revision 2a7bc389f2 (11 days ago), 2020-04-21 20:34:20 -0700
• Engine revision 4c8c31f591
• Dart version 2.8.0 (build 2.8.0-dev.20.10)
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暂时未找到有效办法