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feat(react-native-host): extend RNXHostConfig with optional host hooks (1/3) #4144

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feat(react-native-host): extend RNXHostConfig with optional host hooks (1/3) #4144

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20 changes: 20 additions & 0 deletions packages/react-native-host/cocoa/RNXHostConfig.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,12 @@
#import <React/RCTBridgeDelegate.h>
#import <React/RCTLog.h>

#ifdef __cplusplus
#include <jsi/jsi.h>
#endif

@class ReactNativeHost;

NS_ASSUME_NONNULL_BEGIN

/// Configuration object for ``ReactNativeHost``.
Expand Down Expand Up @@ -30,6 +36,20 @@ NS_ASSUME_NONNULL_BEGIN
/// Handles a fatal error.
- (void)onFatalError:(NSError *)error;

/// Called after the JS instance has finished loading. ``error`` is ``nil``
/// on success.
- (void)host:(ReactNativeHost *)host didLoadInstanceWithError:(nullable NSError *)error
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@Saadnajmi Saadnajmi May 11, 2026

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I'm a little iffy with the optional error parameter.. the signature makes it feel like there is always an error despite the comment. Alternative is to also expose failedtoLoadInstanceWithError. Thoughts?

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@tido64 tido64 May 11, 2026

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Shouldn't this be - (void)didLoadInstanceWithHost:(ReactNativeHost *)host error: (nullable NSError **)error, where the user passes a ref to an NSError if they're interested.

__attribute__((__swift_name__("host(_:didLoadInstanceWithError:)")));

/// Called when the instance is about to be unloaded.
- (void)hostWillUnloadInstance:(ReactNativeHost *)host;

#ifdef __cplusplus
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@tido64 tido64 May 11, 2026

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Is this allowed? Won't we end up with two definitions of this protocol?

/// Called after host bindings install but before the user JS bundle loads.
/// Use to evaluate pre-user JS on the runtime. Bridgeless mode only.
- (void)host:(ReactNativeHost *)host didInitializeRuntime:(facebook::jsi::Runtime &)runtime;
#endif // __cplusplus

// MARK: - RCTBridgeDelegate deprecated details (for backwards compatibility) [>=0.84]

- (NSURL *__nullable)sourceURLForBridge:(RCTBridge *)bridge;
Expand Down
98 changes: 96 additions & 2 deletions packages/react-native-host/cocoa/ReactNativeHost.mm
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Expand Up @@ -35,6 +35,41 @@ @interface ReactNativeHost () <RCTComponentViewFactoryComponentProvider>
@end
#endif // USE_CODEGEN_PROVIDER

#if USE_BRIDGELESS
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@tido64 tido64 May 11, 2026

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Should this block be in a private header instead?


// Forwards host:didInitializeRuntime: from RCTHost to the consumer's RNXHostConfig.
@interface _RNXForwardingRCTHostDelegate : NSObject <RCTHostDelegate>
- (instancetype)initWithHost:(ReactNativeHost *)host config:(id<RNXHostConfig>)config;
@end

@implementation _RNXForwardingRCTHostDelegate {
__weak ReactNativeHost *_host;
__weak id<RNXHostConfig> _config;
}

- (instancetype)initWithHost:(ReactNativeHost *)host config:(id<RNXHostConfig>)config
{
if (self = [super init]) {
_host = host;
_config = config;
}
return self;
}

- (void)host:(RCTHost *)host didInitializeRuntime:(facebook::jsi::Runtime &)runtime
{
id<RNXHostConfig> config = _config;
ReactNativeHost *forwardedHost = _host;
if (forwardedHost != nil &&
[config respondsToSelector:@selector(host:didInitializeRuntime:)]) {
[config host:forwardedHost didInitializeRuntime:runtime];
}
}

@end

#endif // USE_BRIDGELESS

@implementation ReactNativeHost {
__weak id<RNXHostConfig> _config;
NSDictionary *_launchOptions;
Expand All @@ -44,6 +79,9 @@ @implementation ReactNativeHost {
RCTHost *_reactHost;
NSLock *_isShuttingDown;
RNXHostReleaser *_hostReleaser;
#if USE_BRIDGELESS
_RNXForwardingRCTHostDelegate *_hostDelegateProxy;
#endif // USE_BRIDGELESS
#ifdef USE_REACT_NATIVE_CONFIG
std::shared_ptr<ReactNativeConfig> _reactNativeConfig;
#endif // USE_REACT_NATIVE_CONFIG
Expand Down Expand Up @@ -99,11 +137,63 @@ - (instancetype)initWithConfig:(id<RNXHostConfig>)config launchOptions:(NSDictio
});
}

if ([config respondsToSelector:@selector(host:didLoadInstanceWithError:)]) {
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(_rnxInstanceDidLoad:)
name:RCTJavaScriptDidLoadNotification
object:nil];
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(_rnxInstanceDidFailToLoad:)
name:RCTJavaScriptDidFailToLoadNotification
object:nil];
}
if ([config respondsToSelector:@selector(hostWillUnloadInstance:)]) {
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(_rnxInstanceWillUnload:)
name:RCTBridgeWillBeInvalidatedNotification
object:nil];
}
Comment on lines +140 to +158
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@tido64 tido64 May 11, 2026

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Shouldn't all of this be contained within _RNXForwardingRCTHostDelegate?


[self initializeReactHost];
}
return self;
}

- (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)_rnxInstanceDidLoad:(NSNotification *)__unused notification
{
id<RNXHostConfig> config = _config;
if ([config respondsToSelector:@selector(host:didLoadInstanceWithError:)]) {
[config host:self didLoadInstanceWithError:nil];
}
}

- (void)_rnxInstanceDidFailToLoad:(NSNotification *)notification
{
id<RNXHostConfig> config = _config;
if ([config respondsToSelector:@selector(host:didLoadInstanceWithError:)]) {
NSError *error = notification.userInfo[@"error"];
[config host:self didLoadInstanceWithError:error ?: [NSError errorWithDomain:@"ReactNativeHost"
code:0
userInfo:nil]];
}
}

- (void)_rnxInstanceWillUnload:(NSNotification *)__unused notification
{
id<RNXHostConfig> config = _config;
if ([config respondsToSelector:@selector(hostWillUnloadInstance:)]) {
[config hostWillUnloadInstance:self];
}
}

- (RCTBridge *)bridge
{
if (self.isBridgelessEnabled) {
Expand Down Expand Up @@ -303,6 +393,10 @@ - (void)initializeReactHost
#endif
};

// Retained as an ivar because RCTHost stores host delegates weakly.
_hostDelegateProxy = [[_RNXForwardingRCTHostDelegate alloc] initWithHost:self
config:_config];

__weak __typeof(self) weakSelf = self;
if ([RCTHost instancesRespondToSelector:@selector
(initWithBundleURLProvider:
Expand All @@ -312,13 +406,13 @@ - (void)initializeReactHost
initWithBundleURLProvider:^{
return [weakSelf sourceURLForBridge:nil];
}
hostDelegate:nil
hostDelegate:_hostDelegateProxy
turboModuleManagerDelegate:_turboModuleAdapter
jsEngineProvider:jsEngineProvider
launchOptions:_launchOptions];
} else {
_reactHost = [[RCTHost alloc] initWithBundleURL:[self sourceURLForBridge:nil]
hostDelegate:nil
hostDelegate:_hostDelegateProxy
turboModuleManagerDelegate:_turboModuleAdapter
jsEngineProvider:jsEngineProvider];
}
Expand Down
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