flutter plugin registry

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前言

首先这里有三个形似得英文单词registry, registrar and registrant分别对应注册局，注册商和注册人。
把它们翻译到现实的生活场景中的角色其实是一个“注册人通过注册商，更新注册信息后，注册商把信息传递给注册局进行保存”的过程。

注册人：GeneratedPluginRegistrant
注册局：[(FlutterViewController*)rootViewController pluginRegistry] == flutterEngine
注册商：FlutterEngineRegistrar

Flutter Application

flutter create -t plugin my_plugin

xcode 打开 my_plugin/example/ios路径下的 Runner工程

AppDelegate

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@implementation AppDelegate

- (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  [GeneratedPluginRegistrant registerWithRegistry:self];
  // Override point for customization after application launch.
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

@end

GeneratedPluginRegistrant

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@implementation GeneratedPluginRegistrant

+ (void)registerWithRegistry:(NSObject<FlutterPluginRegistry>*)registry {
  [MyPlugin registerWithRegistrar:[registry registrarForPlugin:@"MyPlugin"]];
}

@end

AppDelegate继承FlutterAppDelegate

FlutterAppDelegate

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#pragma mark - FlutterPluginRegistry methods. All delegating to the rootViewController

- (NSObject<FlutterPluginRegistrar>*)registrarForPlugin:(NSString*)pluginKey {
  UIViewController* rootViewController = _window.rootViewController;
  if ([rootViewController isKindOfClass:[FlutterViewController class]]) {
    return [[(FlutterViewController*)rootViewController pluginRegistry] registrarForPlugin:pluginKey];
  }
  return nil;
}

FlutterViewController

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- (id<FlutterPluginRegistry>)pluginRegistry {
  return _engine;
}

FlutterEngineRegistrar

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@implementation FlutterEngineRegistrar {
  NSString* _pluginKey;
  FlutterEngine* _flutterEngine;
}

- (instancetype)initWithPlugin:(NSString*)pluginKey flutterEngine:(FlutterEngine*)flutterEngine {
  self = [super init];
  NSAssert(self, @"Super init cannot be nil");
  _pluginKey = [pluginKey retain];
  _flutterEngine = [flutterEngine retain];
  return self;
}

- (void)addMethodCallDelegate:(NSObject<FlutterPlugin>*)delegate
                      channel:(FlutterMethodChannel*)channel {
  [channel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
    [delegate handleMethodCall:call result:result];
  }];
}

- (NSObject<FlutterBinaryMessenger>*)messenger {
  return _flutterEngine;
}

MyPlugin

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@implementation MyPlugin
+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
  FlutterMethodChannel* channel = [FlutterMethodChannel
      methodChannelWithName:@"my_plugin"
            binaryMessenger:[registrar messenger]];
  MyPlugin* instance = [[MyPlugin alloc] init];
  [registrar addMethodCallDelegate:instance channel:channel];
}

- (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
  if ([@"getPlatformVersion" isEqualToString:call.method]) {
    result([@"iOS " stringByAppendingString:[[UIDevice currentDevice] systemVersion]]);
  } else {
    result(FlutterMethodNotImplemented);
  }
}

@end

FlutterMethodChannel

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- (instancetype)initWithName:(NSString*)name
             binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
                       codec:(NSObject<FlutterMethodCodec>*)codec {
  self = [super init];
  NSAssert(self, @"Super init cannot be nil");
  _name = [name retain];
  _messenger = [messenger retain]; //flutterEngine
  _codec = [codec retain];
  return self;
}

- (void)setMethodCallHandler:(FlutterMethodCallHandler)handler {
  if (!handler) {
    [_messenger setMessageHandlerOnChannel:_name binaryMessageHandler:nil];
    return;
  }
  FlutterBinaryMessageHandler messageHandler = ^(NSData* message, FlutterBinaryReply callback) {
    FlutterMethodCall* call = [_codec decodeMethodCall:message];
    handler(call, ^(id result) {
      if (result == FlutterMethodNotImplemented)
        callback(nil);
      else if ([result isKindOfClass:[FlutterError class]])
        callback([_codec encodeErrorEnvelope:(FlutterError*)result]);
      else
        callback([_codec encodeSuccessEnvelope:result]);
    });
  };
  [_messenger setMessageHandlerOnChannel:_name binaryMessageHandler:messageHandler];
}

FlutterEngine

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#pragma mark - FlutterPluginRegistry

- (NSObject<FlutterPluginRegistrar>*)registrarForPlugin:(NSString*)pluginKey {
  NSAssert(self.pluginPublications[pluginKey] == nil, @"Duplicate plugin key: %@", pluginKey);
  self.pluginPublications[pluginKey] = [NSNull null];
  return [[FlutterEngineRegistrar alloc] initWithPlugin:pluginKey flutterEngine:self];
}

- (void)setMessageHandlerOnChannel:(NSString*)channel
              binaryMessageHandler:(FlutterBinaryMessageHandler)handler {
  NSAssert(channel, @"The channel must not be null");
  FML_DCHECK(_shell && _shell->IsSetup());
  self.iosPlatformView->GetPlatformMessageRouter().SetMessageHandler(channel.UTF8String, handler);
}

FlutterBinaryMessage

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/**
 * A message reply callback.
 *
 * Used for submitting a binary reply back to a Flutter message sender. Also used
 * in for handling a binary message reply received from Flutter.
 *
 * @param reply The reply.
 */
typedef void (^FlutterBinaryReply)(NSData* _Nullable reply);

/**
 * A strategy for handling incoming binary messages from Flutter and to send
 * asynchronous replies back to Flutter.
 *
 * @param message The message.
 * @param reply A callback for submitting an asynchronous reply to the sender.
 */
typedef void (^FlutterBinaryMessageHandler)(NSData* _Nullable message, FlutterBinaryReply reply);