已有iOS项目集成Flutter遇到的一些坑
1.XCode10.3，CocoaPods1.7.5, Flutter 1.8.4-pre.65(一定是master channel，不能是stable)， 根据标题中的环境对应的版本自行升级，如版本高太多的话不敢保证一定会成功。
2.参照官方文档https://github.com/flutter/flutter/wiki/Add-Flutter-to-existing-apps#ios的iOS部分很快就构建好了，于是Commod+B构建，可是马上会遇到第一个坑，如下图：
ld: warning: directory not found for option '-L/Users/wang/Library/Developer/Xcode/DerivedData/test_flutter-dbqsilcpjusqpadpdwvgsoqctumw/Build/Products/Debug-iphonesimulator/FlutterPluginRegistrant'
ld: library not found for -lFlutterPluginRegistrant
clang: error: linker command failed with exit code 1 (use -v to see invocation)
我晕这是什么鬼啊，尝试了各种方式都无效：
怀疑是没有找到静态库 lib(FlutterPluginRegistrant.a)，工程目录和flutter_module目录以及flutterSDK的安装目录都搜遍了，也没有发现这个文件。。。。。。
于是怀疑是新版本的Flutter将FlutterPluginRegistrant.a移除了，根本就不存在这个文件，接下来在宿主iOS工程下的Pods目录中的『Pods-test_flutter.debug.xcconfig』文件中搜索"FlutterPluginRegistrant",果然发现了一些线索
FRAMEWORK_SEARCH_PATHS = $(inherited) "${PODS_ROOT}/../../flutter_module/.ios/Flutter" "${PODS_ROOT}/../../flutter_module/.ios/Flutter/engine"GCC_PREPROCESSOR_DEFINITIONS = $(inherited) COCOAPODS=1HEADER_SEARCH_PATHS = $(inherited) "${PODS_ROOT}/Headers/Public" "${PODS_ROOT}/Headers/Public/FlutterPluginRegistrant"LD_RUNPATH_SEARCH_PATHS = $(inherited) '@executable_path/Frameworks' '@loader_path/Frameworks'LIBRARY_SEARCH_PATHS = $(inherited) "${PODS_CONFIGURATION_BUILD_DIR}/FlutterPluginRegistrant"OTHER_CFLAGS = $(inherited) -isystem "${PODS_ROOT}/Headers/Public" -isystem "${PODS_ROOT}/Headers/Public/FlutterPluginRegistrant" -iframework "${PODS_ROOT}/../../flutter_module/.ios/Flutter/engine" -iframework "${PODS_ROOT}/../../flutter_module/.ios/Flutter"OTHER_LDFLAGS = $(inherited) -ObjC -l"FlutterPluginRegistrant" -framework "App" -framework "Flutter"PODS_BUILD_DIR = ${BUILD_DIR}PODS_CONFIGURATION_BUILD_DIR = ${PODS_BUILD_DIR}/$(CONFIGURATION)$(EFFECTIVE_PLATFORM_NAME)PODS_PODFILE_DIR_PATH = ${SRCROOT}/.PODS_ROOT = ${SRCROOT}/Pods
接下来将 带有 『FlutterPluginRegistrant』内容的部分全部删除（Pods-test_flutter.debug.xcconfig也如法炮制），修改后的配置如下：
FRAMEWORK_SEARCH_PATHS = $(inherited) "${PODS_ROOT}/../../flutter_module/.ios/Flutter" "${PODS_ROOT}/../../flutter_module/.ios/Flutter/engine"
GCC_PREPROCESSOR_DEFINITIONS = $(inherited) COCOAPODS=1
HEADER_SEARCH_PATHS = $(inherited)
LD_RUNPATH_SEARCH_PATHS = $(inherited) '@executable_path/Frameworks' '@loader_path/Frameworks'
LIBRARY_SEARCH_PATHS = $(inherited)
OTHER_CFLAGS = $(inherited) -isystem "${PODS_ROOT}/Headers/Public" -iframework "${PODS_ROOT}/../../flutter_module/.ios/Flutter/engine" -iframework "${PODS_ROOT}/../../flutter_module/.ios/Flutter"
OTHER_LDFLAGS = $(inherited) -ObjC -framework "App" -framework "Flutter"
PODS_BUILD_DIR = ${BUILD_DIR}
PODS_CONFIGURATION_BUILD_DIR = ${PODS_BUILD_DIR}/$(CONFIGURATION)$(EFFECTIVE_PLATFORM_NAME)
PODS_PODFILE_DIR_PATH = ${SRCROOT}/.
PODS_ROOT = ${SRCROOT}/Pods
接下来Command+B再次构建，奇迹发生了，刚才的错误消失了，继续往下走，
参照官方文档将 Appdelegate.m文件改为如下内容
#import <FlutterPluginRegistrant/GeneratedPluginRegistrant >// Only if you have Flutter Plugins
#import "AppDelegate.h"
@interface AppDelegate ()
@end
@implementation AppDelegate
// This override can be omitted if you do not have any Flutter Plugins.
- (BOOL)application:(UIApplication*)application
didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
self.flutterEngine = [[FlutterEngine alloc] initWithName:@"io.flutter" project:nil];
[self.flutterEngine runWithEntrypoint:nil];
[GeneratedPluginRegistrant registerWithRegistry:self.flutterEngine];
return [super application:application didFinishLaunchingWithOptions:launchOptions];
}
Command+B走起，然而第二个坑来了，
Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_GeneratedPluginRegistrant", referenced from:
objc-class-ref in AppDelegate.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
彻底晕倒，这又是什么鬼。。。自习一看才发试一个经典错误，原来是编译期的符号表$_GeneratedPluginRegistrant在链接期间找不到，由于GeneratedPluginRegistrant是在FlutterPluginRegistrant中定义的，这更加说明了FlutterPluginRegistrant.a根本不存在，于是接下去到刚才用命令"flutter create -t module --org com.example flutter_module"构建的 flutter_module 目录中去搜索文件GeneratedPluginRegistrant(mac系统下用finder搜索小伙伴们一定都会了)，果然有所收获，在../flutter_module/.ios/Flutter/FlutterPluginRegistrant/Classes/目录下发现了两个文件GeneratedPluginRegistrant.h和GeneratedPluginRegistrant.m，这下就好办了，在宿主工程中把这两个文件添加进来，方式任意，可以reference也可以copy过来。
二话不说马上Command+B构建工程，大功告成！！可以来支烟庆祝一下了！
希望此文可以帮助迷茫中的你走出困境，现在网上关于这个错误的解决方案少之甚少，如果看到这里，此时你的问题已经得到解决了！！
