AppDelegate.m

// Creates the React Native bridge and adds a custom menu item to the dev menu,
// then opens the main React Native view.

#import <React/RCTBundleURLProvider.h>
#import <React/RCTDevMenu.h>
#import <React/RCTRootView.h>

#import "AppDelegate.h"
#import "ExampleView.h"

@implementation AppDelegate
{
    UINavigationController *navigationController;
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.reactBridge = [[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];

    RCTDevMenuItem *devMenuItem = [RCTDevMenuItem buttonItemWithTitle:@"Custom menu item"
                                                              handler:^{
                                                                  NSLog(@"Custom menu item clicked!");
                                                              }];
    [self.reactBridge.devMenu addItem:devMenuItem];

    RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:self.reactBridge
                                                     moduleName:@"ActivityDemoComponent"
                                              initialProperties:nil];
    rootView.backgroundColor = [[UIColor alloc] initWithRed:1.0f green:1.0f blue:1.0f alpha:1];

    UIViewController *rootViewController = [UIViewController new];
    rootViewController.view = rootView;
    navigationController = [[UINavigationController alloc] initWithRootViewController:rootViewController];

    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    self.window.rootViewController = navigationController;
    [self.window makeKeyAndVisible];

    return YES;
}

- (void) navigateToExampleView
{
    ExampleView *viewController = [[ExampleView alloc] initWithNibName:@"ExampleView" bundle:nil];
    [navigationController pushViewController:viewController animated:YES];
}

- (void) navigateBack
{
    [navigationController popViewControllerAnimated:YES];
}

- (void) callJavaScript
{
    [self.reactBridge enqueueJSCall:@"JavaScriptVisibleToJava"
                             method:@"alert"
                               args:@[@"Hello, JavaScript!"]
                         completion:nil];
}

- (NSURL *)sourceURLForBridge:(RCTBridge *)bridge {
    NSURL *jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index"
                                                                           fallbackResource:nil];
    return jsCodeLocation;
}

@end