Automatically assigning platform ios with version 8.0 on target Runner because no platform was specified. Please specify a platform for this target in your Podfile
在mac上使用引用了第三方库，发现报错，解决步骤如下：
解决办法：
1.platform version错误，解决方法是修改项目里的ios/Podfile文件：
# Uncomment this line to define a global platform for your project
# platform :ios, '9.0'
platform :ios, '8.0' #增加的内容
之后又遇到如下问题
2.SWIFT_VERSION版本未指定问题,解决方法是修改项目里的ios/Podfile文件：
flutter Unable to determine Swift version for the following pods
是指定的SWIFT版本问题，但xcode的tagets中没有指定SWIFT_VERSION版本这一项，点buildSettings中的+号，添加SWIFT_VERSION，指定版本号4.2,再执行pod update --verbose --no-repo-update解决问题
修改项目里的ios/Podfile文件:
post_install do |installer|
installer.pods_project.targets.each do |target|
target.build_configurations.each do |config|
config.build_settings['SWIFT_VERSION'] = '4.2' #增加修改内容
config.build_settings['ENABLE_BITCODE'] = 'NO'
end
end
end
3.flutter 'xxxxx/xxxx-Swift.h' file not found问题：修改项目里的ios/Podfile文件
之后又遇到如下问题
flutter 'xxxxx/xxxx-Swift.h' file not found
修改项目里的ios/Podfile文件：
target 'Runner' do
# Prepare symlinks folder. We use symlinks to avoid having Podfile.lock
# referring to absolute paths on developers' machines.
use_frameworks! # required by qr_code_tools #增加修改的内容
system('rm -rf .symlinks')
system('mkdir -p .symlinks/plugins')
4.PrerollContext does not support embedding错误问题,解决方法是添加plist选项：
Trying to embed a platform view but the PrerollContext does not support embedding
解决方法：
Currently apps need to opt-in for the UIViews embedding preview on iOS by adding a boolean property to the Info.plist (key=io.flutter.embedded_views_preview value=YES).
在iOS工程的info.plist文件中添加键值对key=io.flutter.embedded_views_preview value=YES
