前言

Flutter 是一个很有潜力的框架，但是目前使用Flutter的APP并不算很多，相关资料并不丰富，介绍现有工程引入Flutter的相关文章也比较少。项目从零开始，引入Flutter操作比较简单，但是现有工程引入Flutter 需要费很多精力和时间，这里是我在完成现有iOS工程引入Flutter后写的一次总结文章。

Flutter 环境搭建

首先是要搭建Flutter环境，之前也写了一篇相关文章搭建Flutter-iOS开发环境，可以参考一下
可以去官网查看：https://github.com/flutter/flutter/wiki/Add-Flutter-to-existing-apps
比较简单，这里不做赘述。

现有iOS工程引入Flutter

一、建立Flutter module

首先建立flutter module，主要是用于获取改flutter app中的Generated.xcconfig和framework

cd some/path/
$ flutter create -t module my_flutter

也可以用

flutter create app

建立flutter app，flutter app中也有Generated.xcconfig和framework

二、新建配置文件

根据官网，需要在工程中建立三个配置文件：
Flutter.xcconfig 、Debug.xcconfig、Release.xcconfig
在XCode工程对应目录，右击，选择新建文件（New File），选中创建xcconfig文件，如图：

在Flutter.xcconfig中填写：

 //这里填写前面建立的flutter module 的Generated.xcconfig的路径
#include "../../my_flutter/.ios/Flutter/Generated.xcconfig"
ENABLE_BITCODE=NO

在 Debug.xcconfig中填写:

#include "../Flutter/Flutter.xcconfig"

在 Release.xcconfig中填写:

#include "../Flutter/Flutter.xcconfig"
FLUTTER_BUILD_MODE=release

如果工程中用cocoapods管理，需要在 Debug.xcconfig和Release.xcconfig添加pod的路径：

例如 Release.xcconfig中

#include "Flutter.xcconfig"
#include "工程路径/Pods/Target Support Files/******.release.xcconfig"//pod路径
FLUTTER_BUILD_MODE=release

在准备好这些xcconfig文件后，需要到XCode工程PROJECT（注意是PROJECT,不是Target）中的Configuration选项里，将对应的target选择成前面的xcconfig文件，Debug用Debug.xcconfig, Release用 Release.xcconfig

注意：进行Archive打包的时候，无论是Debug包还是Release包，需要切换到Release.xcconfig，不然会报错。

三、为编译Dart引入相关build phase

在工程的Build Phase中新建一个Run Script,用于编译时运行脚本，
建立方法如图：

建立Run Script后，需要移动其对应的位置，需要在Target dependencies之后，如果用cocoapods管理工程需要在，Check Pods Manifest.lock之后：

在脚本框中，填入以下代码，用于引进Flutter中的xcode_backend脚本：

"$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh" build

如图：

四、生成和添加Framework

完成前面的配置后，便可以在XCode对工程进行编译build (Command+B)，在提示“ Build Success ” 后，在iOS工程文件夹中会生成一个Flutter文件夹，将其加入工程目录中,建议和刚才xcconfig所在目录并列，

右键项目目录 ，选择 Add Files to 'xxx' ，Options选Create groups，添加编译生成的Flutter文件夹。需要注意但是：Flutter目录下有个flutter_assets文件，不能使用Create groups的方式添加，只能用Creat folder references的Options， 否则Flutter页面会空白渲染不出来。可以删了flutter_assets在用Creat folder references重新添加。

在添加完Flutter 文件夹之后，去Embeded Binaries中添加App.framework和Flutter.framework

五、AppDelegate改造

Flutter需要和APP进行交互，需要对AppDelegate 进行改造：

AppDelegate.h文件中：

#import <Flutter/Flutter.h>

@interface AppDelegate : FlutterAppDelegate <UIApplicationDelegate, FlutterAppLifeCycleProvider>

@end

AppDelegate.m 文件中：

#import "AppDelegate.h"

@interface AppDelegate ()
    
@end

@implementation AppDelegate
{
  FlutterPluginAppLifeCycleDelegate *_lifeCycleDelegate;
}
    
- (instancetype)init {
    if (self = [super init]) {
        _lifeCycleDelegate = [[FlutterPluginAppLifeCycleDelegate alloc] init];
    }
    return self;
}
    
- (BOOL)application:(UIApplication*)application
didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
    return [_lifeCycleDelegate application:application didFinishLaunchingWithOptions:launchOptions];
}
    
- (void)applicationDidEnterBackground:(UIApplication*)application {
    [_lifeCycleDelegate applicationDidEnterBackground:application];
}
    
- (void)applicationWillEnterForeground:(UIApplication*)application {
    [_lifeCycleDelegate applicationWillEnterForeground:application];
}
    
- (void)applicationWillResignActive:(UIApplication*)application {
    [_lifeCycleDelegate applicationWillResignActive:application];
}
    
- (void)applicationDidBecomeActive:(UIApplication*)application {
    [_lifeCycleDelegate applicationDidBecomeActive:application];
}
    
- (void)applicationWillTerminate:(UIApplication*)application {
    [_lifeCycleDelegate applicationWillTerminate:application];
}
    
- (void)application:(UIApplication*)application
didRegisterUserNotificationSettings:(UIUserNotificationSettings*)notificationSettings {
    [_lifeCycleDelegate application:application
didRegisterUserNotificationSettings:notificationSettings];
}
    
- (void)application:(UIApplication*)application
didRegisterForRemoteNotificationsWithDeviceToken:(NSData*)deviceToken {
    [_lifeCycleDelegate application:application
didRegisterForRemoteNotificationsWithDeviceToken:deviceToken];
}
    
- (void)application:(UIApplication*)application
didReceiveRemoteNotification:(NSDictionary*)userInfo
fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler {
    [_lifeCycleDelegate application:application
       didReceiveRemoteNotification:userInfo
             fetchCompletionHandler:completionHandler];
}
    
- (BOOL)application:(UIApplication*)application
            openURL:(NSURL*)url
            options:(NSDictionary<UIApplicationOpenURLOptionsKey, id>*)options {
    return [_lifeCycleDelegate application:application openURL:url options:options];
}
    
- (BOOL)application:(UIApplication*)application handleOpenURL:(NSURL*)url {
    return [_lifeCycleDelegate application:application handleOpenURL:url];
}
    
- (BOOL)application:(UIApplication*)application
            openURL:(NSURL*)url
  sourceApplication:(NSString*)sourceApplication
         annotation:(id)annotation {
    return [_lifeCycleDelegate application:application
                                   openURL:url
                         sourceApplication:sourceApplication
                                annotation:annotation];
}
    
- (void)application:(UIApplication*)application
performActionForShortcutItem:(UIApplicationShortcutItem*)shortcutItem
  completionHandler:(void (^)(BOOL succeeded))completionHandler NS_AVAILABLE_IOS(9_0) {
    [_lifeCycleDelegate application:application
       performActionForShortcutItem:shortcutItem
                  completionHandler:completionHandler];
}
    
- (void)application:(UIApplication*)application
handleEventsForBackgroundURLSession:(nonnull NSString*)identifier
  completionHandler:(nonnull void (^)(void))completionHandler {
    [_lifeCycleDelegate application:application
handleEventsForBackgroundURLSession:identifier
                  completionHandler:completionHandler];
}
    
- (void)application:(UIApplication*)application
performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler {
    [_lifeCycleDelegate application:application performFetchWithCompletionHandler:completionHandler];
}
    
- (void)addApplicationLifeCycleDelegate:(NSObject<FlutterPlugin>*)delegate {
    [_lifeCycleDelegate addDelegate:delegate];
}

六、新建FlutterViewController

主要配置基本上已经完成，只要在main.dart实现Flutter的业务代码即可

在原有工程中 ，建立FlutterViewController来承载main.dart实现的Flutter页面，如：

    self.flutterViewController = [[FlutterViewController alloc] initWithProject:nil nibName:nil bundle:nil];
    [self.navigationController pushViewController:self.flutterViewController animated:YES];

后语

到这里现有iOS工程引入Flutter的工作就完成了，一些细节上的修改需要根据场景进行修改，例如Flutter和Native的数据通信等。