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

With native iOS or Mac applications packaged with Cocos Creator, JavaScript calling Objective-C functions directly through the native language’s reflection mechanism can be achieved with the following sample code:

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

Use jsb.reflection.callStaticMethod to call Native Objective-C method by sending className, methodName and parameters.

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

Objective-C Classes

  • It is necessary to provide functionality in an Objective-C class as per the example below. The className parameter in this case should be NativeOcClass.

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

Objective-C Methods

  • Reflection from JavaScript to Objective-C supports only static methods of an Objective-C class.

  • methodName parameter in the previous example are the Objective-C method names in your class, take NativeOcClass as an example, notice the method:

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

    The methodName should be callNativeUIWithTitle:addContent: which is the definition for this method, and don’t forget the :. Search for an Objective-C programming guide for more details.

  • Another example below, the methodName should be callNativeWithReturnString.

    1. +(NSString *)callNativeWithReturnString;

Usage

  • In JavaScript code, for invoking the native method callNativeUIWithTitle:andContent: of NativeOcClass, use the jsb.reflection.callStaticMethod API. Example:

    1. var ret = jsb.reflection.callStaticMethod("NativeOcClass",
    2.                                          "callNativeUIWithTitle:andContent:",
    3.                                          "cocos2d-js",
    4.                                          "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 sent from JavaScript:

    1. +(BOOL)callNativeUIWithTitle:(NSString *) title andContent:(NSString *)content{
    2.   UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:content delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
    3.   [alertView show];
    4.   return true;
    5. }

Executing JavaScript in Objective-C

Conversely, JavaScript code can be executed in C++/Objective-C by using evalString.

Example:

  1. Application::getInstance()->getScheduler()->performFunctionInCocosThread([=](){
  2.     se::ScriptEngine::getInstance()->evalString(script.c_str());
  3. });

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.

Type Support

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

  • To use float, int, double as parameter types in your native method, change to use NSNumber instead.
  • To use bool as parameter type, change to use BOOL instead.

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

    1. +(float) addTwoNumber:(NSNumber *)num1 and:(NSNumber *)num2 {
    2.   float result = [num1 floatValue] + [num2 floatValue];
    3.   return result;
    4. }

  • For return values only int, float, bool, string are supported in the current version.