How to access native UI components' instance methods in React Native

Question

We can control custom native UI components\' properties by exporting native properties using RCT_EXPORT_VIEW_PROPERTY.

But how to export instance method

Answer 1

Thanks to @alinz's suggestion.

This can be done within the custom native component's view manager.

1. Obj-c side: In the native view manager expose a native method like this:

The key is to pass in the reactTag which is the reference to the native component.

MyCoolViewManager.m:

RCT_EXPORT_METHOD(myCoolMethod:(NSNumber *)reactTag callback:(RCTResponseSenderBlock)callback) {
  [self.bridge.uiManager addUIBlock:^(RCTUIManager *uiManager, RCTSparseArray *viewRegistry) {
    MyCoolView *view = viewRegistry[reactTag];
    if (![view isKindOfClass:[MyCoolView class]]) {
      RCTLogMustFix(@"Invalid view returned from registry, expecting MyCoolView, got: %@", view);
    }
    // Call your native component's method here
    [view myCoolMethod];
  }];
}

2. JS side: Add API in the react component class:

MyCoolView.js:

var React = require('react-native');
var NativeModules = require('NativeModules');
var MyCoolViewManager = NativeModules.MyCoolViewManager;
var findNodeHandle = require('findNodeHandle');

class MyCoolView extends React.Component{
    // ...
    myCoolMethod() {
        return new Promise((resolve, reject) => {
            MyCoolViewManager.myCoolMethod(
                findNodeHandle(this),
                (error, result) => {
                    if (error) {
                        reject(error);
                    } else {
                        resolve(result);
                    }
                }
            );
        });
    }
}

Answer 2

I'm not an Objective C expert but a Swift developer.

I better use this way just for readability (maybe there are drawbacks in Obj-C?):

• In Manager: store a reference to your view in an instance private property
• it will then help to call your view's method

Obj-C side - component manager:

@implementation RNAnalogClockManager {
  RNAnalogClock* _AnalogClock;
}

RCT_EXPORT_MODULE()

- (UIView *)view
{
  // keep a reference to the view before returning it
  _AnalogClock = [[RNAnalogClock alloc] init];
  return _AnalogClock;
}

// export method and easily call view method 
RCT_EXPORT_METHOD(startRealTime) {
  [_AnalogClock startRealTime];
};

JS side remains the same

NOTE: I don't need callback in my example but it does not change the principle it is just another parameter.