oc-reflection.md

How to call Objective-C functions using JavaScript on iOS/Mac

In Cocos2d-JS v3.0 RC2, we'd like to introduce you the js to Objective-C reflection feature. Like we can call native functions on Java by JS, you can now invoke Objective-C Static Method in JS too.

var ojb = jsb.reflection.callStaticMethod(className, methodName, arg1, arg2, .....);

You can use jsb.reflection.callStaticMethod to call Native OC method by sending className methodName and parameters.

Note: Please pay attention to Apple Developer Program License Agreement (section 3.3.2) when you use reflection features. The usage of respondsToSelector: and performSelector: might cause problem in App Store review process, here is a related discussion in React-Native's issue tracker.

Objective-C Class

• You will need to provide your functionality in an OC class as the example below, the className parameter in this case should be NativeOcClass.

import <Foundation/Foundation.h>
@interface NativeOcClass : NSObject
+(BOOL)callNativeUIWithTitle:(NSString *)title andContent:(NSString *)content;
@end

Objective-C Method

• The reflection from js to OC support only static method of an OC class.

• methodName parameter in previous example is the OC method name in your class, take NativeOcClass as an example, we can see a method named

  +(BOOL)callNativeUIWithTitle:(NSString *)title andContent:(NSString *)content;
  

  So the methodName should be callNativeUIWithTitle:addContent: which is the definition for this method, and don't forget the :. We cannot discuss the details here, but if you are interested, you can search for Objective-C programming guide for more details.

• Another example below, the methodName should be callNativeWithReturnString.

  +(NSString *)callNativeWithReturnString;
  

Usage

• In JS code, for invoking the native method callNativeUIWithTitle:andContent: of NativeOcClass, we can use jsb.reflection.callStaticMethod API like this:

  var ret = jsb.reflection.callStaticMethod("NativeOcClass",
                                           "callNativeUIWithTitle:andContent:",
                                           "cocos2d-js",
                                           "Yes! you call a Native UI from Reflection");

• This method can show an alert dialog and return a boolean status. Here is its implementation, title and content parameters will receive the strings you sent from js:

  +(BOOL)callNativeUIWithTitle:(NSString *) title andContent:(NSString *)content{
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:content delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
    [alertView show];
    return true;
  }
  

Executing JS in Objective-C

Conversely, we can also execute JavaScript code in C++ / Objective-C by using evalString.

Example:

Application::getInstance()->getScheduler()->performFunctionInCocosThread([=](){{
    se::ScriptEngine::getInstance()->evalString(script.c_str());
});

Note: Unless it is clear that the current thread is the main thread, the function needs to be distributed to the main thread for execution.

Notice

Types supported for parameters and return value are limited in Cocos2d-JS reflection.

• If you need to use float, int, double as parameter types in your native method, you need to change to use NSNumber instead.

• If you need to use bool as parameter type, you need to change to use BOOL instead.

• Here is an example, we use NSNumber instead of int, float or double.

  +(float) addTwoNumber:(NSNumber *)num1 and:(NSNumber *)num2 {
    float result = [num1 floatValue] + [num2 floatValue];
    return result;
  }
  

• For return value we only support int, float, bool, string in the current version.