How does calling from JS to Obj-C work?

[jlongster]

I added a method to my TeapotController object:

- (void)touchHappened {
  RCT_EXPORT();
  NSLog(@"happened");
  CC3Vector pos = teapotNode_.position;
  [teapotNode_ setSizeX: 10];
  [teapotNode_ invalidateGlobalTransformMatrix];
}

Looking through the source, it looks like I can add RCT_EXPORT to export a method. I can then call it like this:

var controller = require('NativeModules').TeapotController;
controller.touchHappened();

If I just log something in touchHappened, this works. But when I try to access an instance variable like teapotNode_, nothing happens... but I don't see how this works anyway. How is it exporting a method from an instance? What I have multiple instances of TeapotController? I don't see how I could require individual instances.

[jlongster]

Nevermind, I thought that the method wasn't even running for some reason but it's definitely running. For some reason my code isn't updating some state like I thought it would. Still, is that the right way to expose an Obj-C method?

[jlongster]

Hm, when I do NSLog(@"%x", teapotNode_); it prints 0. I don't know Obj-C too well, but does it not crash when sending messages to a null pointer? Anyway, it does seem to be calling the method as a static method, not as an instance method. How do I expose an instance method?

EDIT: I'm assuming it's possible because inside RCTUIManager.m it exports several instance methods. Some of them even reference self. But I see nothing outside of RCT_EXPORT() that sets the instance for the exporter...

EDIT2: Oh, I see in initWithJavaScriptExecutor that it allocates a single instance of the class, so the class is meant to be a single module instance. Might be nice to have a way to register an existing instance as a module?

[sophiebits]

I don't know Obj-C too well, but does it not crash when sending messages to a null pointer?

No, it doesn't crash; it returns nil.

[jlongster]

Ok.

I added a getModule method on RCTBridge so now I just do TeapotController *vc = [bridge getModule:@"TeapotController"]; after creating the root view. I'm sure this is not the right way to do it. But I hacked. And it was fun.

[a2]

I think two things are going on here:

A) Not sure if you're already doing this, but your TeapotController needs to conform to the RCTNativeModule protocol in order to be registered with the bridge.

B) If a class conforms to the RCTNativeModule protocol, it will be instantiated by the RCTBridge for use in the RCTRootView. Where do you set the teapotNode_ ivar?

[jlongster]

The teapotNode_ is just a scene node object that is created in the viewDidLoad controller method. I did add that protocol:

@interface TeapotController : GLViewController<RCTNativeModule> {
    TeapotNode *teapotNode_;
    BOOL tapIsValid_;
    CGPoint lastDragPoints_[2];
    CGPoint touchStartPoint_;
}

And it's all working fine. The problem is that the bridge instantiates the TeapotController class, but I don't see any way to get to it through the RCTRootView class. I had to add a method myself to dig into the internal modules and return the instance.

[jlongster]

To leave a clearer comment about what is needed: we need to be able to access the modules (that are actually class instances) that the bridge creates to have a generic way of talking between iOS and JS. These classes will have state, and when a callback (say from user input) calls back into the iOS world we need access to it.

[vjeux]

@jlongster mind updating the title of the issue to reflect what needs to be done here outside of documentation?

[jaygarcia]

Are the discussed items here obsolete? I grep'ed for RCTNativeModule and initWithJavaScriptExecutor across the entire repo and found nothing.

[nicklockwood]

@jaygarcia RCTNativeModule is now called RCTBridgeModule.

[jaygarcia]

Thanks :) I should have replied to my comment. I have been able to grasp things now from the JS <> ObJC side. It wasn't easy, but with enough digging through the ReactKit code, I figured much of what I needed to out.

The Macros are simply genius. I wish the Cordova guys were smart enough to do that.

[frantic]

Hey @jaygarcia , see new guide at https://github.com/facebook/react-native/blob/master/docs/NativeModulesIOS.md. Let us know if you think something should be added there.

[jaygarcia]

Should this be closed?

@frantic , i think the article is pretty air tight for the moment :)

[frantic]

Cool! :)