Re: libseed-list Call a Vala Function from Javascript

[Alexandre Mazari <scaroo gmail com>]

Le vendredi 20 mai 2011 à 10:38 +0200, Alexandre Mazari a écrit :
> Hi Andrew,
> 
> JavascriptCore offer facilities to expose native functions within the js
> context. Seed makes it more convenient.
> So you ont be able to expose your vala procedure as-is but its C
> counterpart.
> 
> First you need a hold on the js context object. Webkit gtk gives you a
> chance to modify it when the global js object representing the "window"
> is created. Just attach a handler to the "window-object-cleared" WebView
> signal. See
> 
> http://webkitgtk.org/reference/webkitgtk-webkitwebview.html#WebKitWebView-window-object-cleared
> 
> The signature of the handler is 
> void on_window_object_cleared (WebKitWebView  *web_view,
>                                WebKitWebFrame *frame,
>                                gpointer        context,
>                                gpointer        window_object,
>                                gpointer        user_data);
> 
> From there, you can call JavascriptCore's
> 
> JSObjectRef JSObjectMakeFunctionWithCallback(
>     JSContextRef ctx,
>     JSStringRef name,
>     JSObjectCallAsFunctionCallback callAsFunction);
> 
> where callAsFunction is a pointer to your routine.
> 
> Then expose the returned object, which represent the javascript function
> associated with your callback, in the js context using the following:
> 
> JS_EXPORT void JSObjectSetProperty(
>     JSContextRef ctx,
>     JSObjectRef object,
>     JSStringRef propertyName,
>     JSValueRef value,
>     JSPropertyAttributes attributes,
>     JSValueRef *exception);  
> 
> object should point to the "window" object, propertyName will be the
> name of your function in the js context, value the object we got
> beforehand.
> 
> 
> So to sum that up you should have something like this:
> 
> static void my_native_print(char *it)
> {
> 	printf("%s\n", it);
> }
> 
> JSValueRef
> my_native_print_wrapper (JSContextRef ctx, JSObjectRef function, 
> 			    JSObjectRef thisObject,
> 	                    size_t argumentCount,
>                             const JSValueRef arguments[],
>                             JSValueRef* exception)
> {
> 	// convert first argument to utf8 char*
> 	char argument1[256];
> 	JSStringGetUTF8CString (arguments[0], argument1, 256);
>  	
> 	my_native_print(argument1);
> }
> 
> void on_window_object_cleared (WebKitWebView  *web_view,
>                                WebKitWebFrame *frame,
>                                gpointer        context,
>                                gpointer        window_object,
>                                gpointer        user_data)
> {
> 
> 	JSObjectRef js_func =
>         JSObjectMakeFunctionWithCallback(context, NULL,
>  					 my_native_print_wrapper);
> 
>        JSObjectSetProperty(context, window_object, "native_print",
> 			   js_func, NULL, NULL);       
> }

Oops and of course you must attach a handler the the WebView signal:

static int main()
{
...
       g_signal_connect(G_OBJECT(web_view), "window-object-cleared", 	
                      G_CALLBACK(on_window_object_cleared), self);

}
> 
> "window.native_print" should now be available in the js context and call
> your native function.
> 
> You might need to tweak a little, I havent tried to compile it.
> 
> Le vendredi 20 mai 2011 à 08:27 +0100, Andrew a écrit :
> > Hi Everyone,
> > 
> > So I have a Vala function:
> > 
> > public void say_my_name(string name) {
> >     stdout.printf("Hi, my name is %s", name);
> > }
> > 
> > And I want to be able to call this in Javascript like so:
> > 
> > say_my_name("John Doe");
> > 
> > This Javascript however, is on a local HTML file, that I access through
> > a Webkit.WebView
> > 
> > Could someone point to an existing example (can be in C), or just talk
> > through the basic steps needed to acomplish this? If you need any more
> > information, please don't hesitate to contact me.
> > 
> > Thanks
> > 
> 
>