Pergunta

Como a estrutura JavaScriptCore traduz objetos JavaScript em objetos Objective-C e vice-versa?A ponte usa o mesmo protocolo binário para se comunicar com ambos os idiomas de destino?

Foi útil?

Solução

A estrutura Objective-C introduzida no iOS7 faz todo o trabalho pesado para você.Você não precisa pensar nos objetos como o mesmo binário, mas interpretados de maneira diferente - o framework executa uma cópia de ao converter entre ObjC e Javascript.

De JSValue.h:

// Conversion between Objective-C and JavaScript types.
//
// When converting between JavaScript values and Objective-C objects a copy is
// performed. Values of types listed below are copied to the corresponding
// types on conversion in each direction. For NSDictionaries, entries in the
// dictionary that are keyed by strings are copied onto a JavaScript object.
// For dictionaries and arrays, conversion is recursive, with the same object
// conversion being applied to all entries in the collection.

  Objective-C type  |   JavaScript type
--------------------+---------------------
        nil         |     undefined
       NSNull       |        null
      NSString      |       string
      NSNumber      |   number, boolean
    NSDictionary    |   Object object
      NSArray       |    Array object
       NSDate       |     Date object
      NSBlock *     |   Function object *
         id **      |   Wrapper object **
       Class ***    | Constructor object ***

* Instances of NSBlock with supported arguments types will be presented to
JavaScript as a callable Function object. For more information on supported
argument types see JSExport.h. If a JavaScript Function originating from an
Objective-C block is converted back to an Objective-C object the block will
be returned. All other JavaScript functions will be converted in the same
manner as a JavaScript object of type Object.

** For Objective-C instances that do not derive from the set of types listed
above, a wrapper object to provide a retaining handle to the Objective-C
instance from JavaScript. For more information on these wrapper objects, see
JSExport.h. When a JavaScript wrapper object is converted back to Objective-C
the Objective-C instance being retained by the wrapper is returned.

*** For Objective-C Class objects a constructor object containing exported
class methods will be returned. See JSExport.h for more information on
constructor objects.

Por exemplo (para tipos simples):

NSString *myString = [javascriptContext[@"myJSVar"] toString];

e

javascriptContext[@"myJSVar"] = myString;

ou para um objeto mais complexo, use o protocolo JSExport:

@protocol MyPointExports <JSExport>
@property double x;
@property double y;
@end

@interface MyPoint : NSObject <MyPointExports>
// Put methods and properties not visible to JavaScript code here.
@end

...

javascriptContext[@"MyPoint"] = [MyPoint class]; // Define the class in Javascript

então

MyPoint *p = [javascriptContext[@"myJSPointVar"] toObject];

e

javascriptContext[@"myJSPointVar"] = p;

Para cada propriedade declarada no protocolo, o framework construirá getter/setters JS, então dentro do Javascript você pode simplesmente fazer:

myJSPointVar.x = 10;

Para os leitores que procuram uma introdução à estrutura JavaScriptCore, confira a sessão de vídeo/pdf da WWDC 2013 "Integrando JavaScript em aplicativos nativos" na rede de desenvolvedores da Apple: https://developer.apple.com/videos/wwdc/2013/?id=615

Outras dicas

Dê uma olhada nesta classe: nsjsonserialization.

Licenciado em: CC-BY-SA com atribuição
Não afiliado a StackOverflow
scroll top