React Native - native module started kit (iOs)

AppDelegate.m

// ...
#import "FooModule.h"
// ...

@interface AppDelegate ()
// ...
@property (nonatomic, strong) FooModule *fooModule;
// ...
@end

@implementation AppDelegate
// ...
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  // ...
  self.fooModule = [FooModule bootstrap];
  // ...
}
// ...
@end

FooModule.h

//
//  FooModule.h
//
//  Created by Fabio Cigliano on 1/08/19.
//

#import <Foundation/Foundation.h>
#import <React/RCTBridgeModule.h>
#import <React/RCTEventEmitter.h>

#define MODULE_NAME @"Foo"

#define EVENT_NAME @"change"

#define MLOG_FORMAT @"[foo] :: %s [Line %d] "
#define MLog(fmt, ...) NSLog((MLOG_FORMAT fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);

NS_ASSUME_NONNULL_BEGIN

@interface FooModule : RCTEventEmitter <RCTBridgeModule>

+ (id) bootstrap;

@end

NS_ASSUME_NONNULL_END

FooModule.m

//
//  FooModule.m
//
//  Created by Fabio Cigliano on 1/08/19.
//

#import "FooModule.h"

@interface FooModule (RCTEventEmitter)
@end

@interface FooModule ()
{
}

@property (nonatomic, assign) NSDate* lastUpdate;
@property (nonatomic, assign) BOOL isListening;
@property (nonatomic, assign) int listenerCount;

- (void)attachListener;
- (void)removeListener;
-(BOOL)hasListener;

@end

@implementation FooModule : RCTEventEmitter

#pragma mark - External

+ (id) bootstrap {
  MLog(@"initialized");

  return [[FooModule alloc] init];
}

#pragma mark - Internal

- (instancetype)init
{
  self = [super init];
  
  if (self) {
    // init internal state
    self.lastUpdate = nil;
    self.isListening = NO;
    self.listenerCount = 0;

    // should we start any service at startup?
    // [self attachListener];
  }

  return self;
}

- (void)dealloc
{
  // remove any service
  [self removeListener];
}

#pragma mark - State

// expose the internal state
- (NSDictionary*) getStateObject {
  return @{
           @"lastUpdate": @([self.lastUpdate timeIntervalSince1970])
           };
}

#pragma mark - React

RCT_EXPORT_MODULE(ScreenStateModule);

+ (BOOL)requiresMainQueueSetup
{
  return NO;
}

#pragma mark - Exported

RCT_EXPORT_METHOD(getState:(RCTResponseSenderBlock)callback)
{
  callback(@[ [self getStateObject] ]);
}

#pragma mark - Event handling

- (NSArray<NSString *> *)supportedEvents
{
  return @[ EVENT_NAME ];
}

// Will be called when this module's first listener is added.
-(void)startObserving {
  // Set up any upstream listeners or background tasks as necessary

  self.listenerCount++;

  [self attachListener];
}

// Will be called when this module's last listener is removed, or on dealloc.
-(void)stopObserving {
  // Remove upstream listeners, stop unnecessary background tasks

  self.listenerCount--;

  if (self.listenerCount <= 0) {
    [self attachListener];
  }
}

-(BOOL)hasListener {
  return self.bridge != nil && self.listenerCount > 0;
}

#pragma mark - Services

- (void) attachListener
{
  if (self.isListening) {
    // skip this if already listening
    return;
  }
  self.isListening = YES;

  MLog(@"attachListener");

  //
  // TODO: add your service here
  //
  
  /*
  for instance
  // listen for lock state changes
  notify_register_dispatch("com.apple.springboard.lockstate", &lockStateToken, dispatch_get_main_queue(), ^(int token) {
    // here we forward events to js
    [self readState];
  });
  */

  // at startup read and forward the state
  [self readState];
}

- (void) removeListener
{
  if (!self.isListening) {
    // skip this if already stopped
    return;
  }
  self.isListening = NO;

  MLog(@"removeListener");
  
  //
  // TODO: add your service here
  //

}

- (void) readState
{
  BOOL didChange = NO;

  //
  // TODO: do something here
  //

  // trigger all the attached event listener
  if ([self hasListener] && didChange) {
    self.lastUpdate = [NSDate date];
    NSDictionary* state = [self getStateObject];

    MLog(@"new event %@", state);

    [self sendEventWithName:EVENT_NAME body:state];
  }
}

@end