Flutter之遇到的问题记录

2020/02/10 Flutter Dart

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
$ 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.

  • 问题解决

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

$ 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
  • 问题分析

确认pod路径

$ which pod
/usr/local/bin/pod

确认cocoapods安装状态

$ 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)

说明cocoapods有安装,再确认一下cocoapods 信息

$ 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.

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:

$ 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
  • 问题解决

修改Paths

$ 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

3. AppBar 不自动显示返回键等leading Widget

  • 异常情况

关于Scaffold AppBar的automaticallyImplyLeading参数,默认为true,根据doc注释:

  /// 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.

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?

  • 问题原因

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:

  1. 将Scaffold作为根Widget
  2. 如果布局需要无法作为根Widget,则显式指定leading Widget,如返回键:
Scaffold(
  appBar: AppBar(
    //显式指定返回键
    leading: BackButton(
      onPressed: () => Navigator.pop<bool>(context, false),
    ),
  ),
))

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:

$ flutter doctor
Waiting for another flutter command to release the startup lock...
  • 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:

$ 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)

暂时未找到有效办法

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