React Native and Objective C delegates

Question

I am quite new to react native and and the bridging mechanism with native code, especially when the framework has delegates. Assume I am trying to bridge the following framework:

@protocol BRPtouchNetworkDelegate;

@class PLNetworkModule;

@interface BRPtouchNetworkManager : NSObject <NSNetServiceBrowserDelegate,NSNetServiceDelegate>


@property(retain, nonatomic) NSMutableArray* registeredPrinterNames;
@property(assign, nonatomic) BOOL isEnableIPv6Search;


- (int)startSearch: (int)searchTime;
- (NSArray*)getPrinterNetInfo;

- (BOOL)setPrinterNames:(NSArray*)strPrinterNames;
- (BOOL)setPrinterName:(NSString*)strPrinterName;

- (id)initWithPrinterNames:(NSArray*)strPrinterNames;
- (id)initWithPrinterName:(NSString*)strPrinterName;

@property (nonatomic, assign) id <BRPtouchNetworkDelegate> delegate;

@end

@protocol BRPtouchNetworkDelegate <NSObject>

-(void) didFinishSearch:(id)sender;

@end

The following is the bridge module I implemented:

RCTBRPtouchNetworkManager.h

#import <React/RCTBridgeModule.h>
#import <BRPtouchPrinterKit/BRPtouchPrinterKit.h>

@interface RCTBRPtouchNetworkManager : NSObject <RCTBridgeModule, BRPtouchNetworkDelegate>
@end

RCTBRPtouchNetworkManager.m

#import "RCTBRPtouchNetworkManager.h"
#import <BRPtouchPrinterKit/BRPtouchPrinterKit.h>
#import <React/RCTLog.h>

@implementation RCTBRPtouchNetworkManager {
  BRPtouchNetworkManager  *_networkManager;
}

RCT_EXPORT_MODULE();

RCT_EXPORT_METHOD(addEvent:(NSString *)name location:(NSString *)location)
{
  RCTLogInfo(@"Pretending to create an event %@ at %@", name, location); //a dummy method to test the bridge
}

RCT_EXPORT_METHOD(startSearchWithTimeout:(int)time) {
  RCTLogInfo(@"Bridge started search with time %d", time);

  _networkManager = [[BRPtouchNetworkManager alloc] init];
  _networkManager.delegate = self; //I'm setting delegate here
  _networkManager.isEnableIPv6Search = NO;
  NSString *  path = [[NSBundle mainBundle] pathForResource:@"PrinterList" ofType:@"plist"];
  if( path )
  {
    NSDictionary *printerDict = [NSDictionary dictionaryWithContentsOfFile:path];
    NSArray *printerList = [[NSArray alloc] initWithArray:printerDict.allKeys];
    [_networkManager setPrinterNames:printerList];
  } else {
    RCTLogInfo(@"PrinterList path not found");
  }

  //  Start printer search
  [_networkManager startSearch: 5.0];

}

- (void)didFinishSearch:(id)sender {
  NSLog(@"didFinishedSearch"); //this delegate method is not called
}

@end

I can easily call the dummy method and see the results in the logs. However, the delegate method didFinishSearch() is never called. I call this from javascript as follows:

componentDidMount() {
    let networkManager = NativeModules.BRPtouchNetworkManager;
    networkManager.startSearchWithTimeout(5.0);
}

I there something I am missing? Am I implementing delegate properly? Is this kind of functionality even possible (can't seem to not since the delegate method was used by iOS community for a long time). Your help is much appreciated.

EDIT

I found that adding the following to my bridge manager file made the delegate to fire (thanks to this post)

- (dispatch_queue_t)methodQueue
{
    return dispatch_get_main_queue();
}

However, even though this solves the problem, I'd like a more technical understanding on what is going on here since I can't seem to exactly grasp it. Thank you

Answer 1

I know this isn’t an an answer to the post but for the bit where you’ve asked for a more technical understanding - dispatch_get_main_queue(); puts the delegate method responses on to the main thread. Since JS is single threaded any process on the background thread won’t be visible to it.