Subj : Re: problem on setter of object;'s property
To   : netscape.public.mozilla.jseng
From : "lyg" <liyg@tech.coretek.com.cn>
Date : Wed Feb 11 2004 09:44 am



> lyg wrote:
>
> >when i set the value property of a option object , why the
GetOptionProperty
> >function is not called ?
    I made a mistake, it ought to be when  i get the value property, why the
GetOptionProperty function is not called.
    i found the sticking point. i should use "proto = JS_InitClass(cx, obj,
NULL, &OptionClass, Option, 4,
    OptionProperties, NULL,  NULL, ,NULL)" instead of " proto =
............4, NULL , NULL, OptionProperties, NULL)";

> >
> >what is wrong ? Thanks!
> >
> >/*declare option object's property GETTER*/
> >static JSBool GetOptionProperty (JSContext *cx, JSObject *obj, jsval id,
> >jsval *vp);
> >
> >static JSClass OptionClass = {
> >          "Option",0,
> >           JS_PropertyStub,JS_PropertyStub, JS_PropertyStub,
> >JS_PropertyStub,JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub,
> >JS_FinalizeStub,JSCLASS_NO_OPTIONAL_MEMBERS
> >};
> >
> >enum  OPTION_PROP_ID {
> >
> >  OPTION_VALUE = 0,
> >  OPTION_TEXT,
> >};
> >
> >static JSPropertySpec OptionProperties[] =
> >{
> >   {"value",        OPTION_VALUE,
> >JSPROP_ENUMERATE|JSPROP_READONLY, GetOptionProperty},
> >   {"text",             OPTION_TEXT,
> >JSPROP_ENUMERATE|JSPROP_READONLY, GetOptionProperty},
> >   {0}
> >};
> >
> >static JSBool
> >Option(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval
*rval)
> >{
> >  if (0 < argc && 5 > argc)
> >
> >
>
> This might be more readable of it used number-line order (0 < argc &&
> argc < 5).  Why 5?

   In order to abbreviate the code here , I only set two properties of
option . Actually , it have four params at best  when creating option object
..
 so 0 < argc &&  5 > argc.
thanks for you advice.


>
> >  {
> >    char *temp;
> >    temp = JS_GetStringBytes( JSVAL_TO_STRING(argv[0]) );
> >
> >    JS_SetProperty(cx, obj, "text",  &argv[0]);
> >    if (argc > 1)
> >      JS_SetProperty(cx, obj, "value", &argv[1]);
> >
> >
>
> How is this supposed to work, given that value is readonly?

   I want not save some  property value in js option object, and when i get
it, i callback my application's data structure where some property value is
stored , managed and forbitting modified . Therefore i define getter by with
fetch property value from browser's data structure. so I define it readOnly.
As yet , i don't understand readonly's real meaning. it may be used wrong
here. Can you help me? Thanks.
>
> >    return JS_TRUE;
> >  }
> >  else return JS_FALSE;
> >
> >
>
   return false means the option object is not created correctly .

> 1.  else after return is a non-sequitur.
> 2.  Never return false without first calling JS_ReportError or
> JS_SetPendingException, or calling something that does that before it
> returns false or null.
>
  thanks. i am glad to accept you advice.
> >}
> >
> >JSObject *
> >js_InitOptionClass(JSContext *cx, JSObject *obj)
> >{
> >    JSObject *proto;
> >
> >    proto = JS_InitClass(cx, obj, NULL, &OptionClass, Option, 4,
> >            NULL, NULL, OptionProperties, NULL);
> >    if (!proto)
> >       return NULL;
> >    OBJ_SET_SLOT(cx, proto, JSSLOT_PRIVATE, JSVAL_FALSE);
> >
> >
>
> Do not use OBJ_SET_SLOT or include jsobj.h!  Use only jsapi.h.
>
> Why would you set the private slot on an object whose class lacks the
> JSCLASS_HAS_PRIVATE flag?  That's an error, and if you had used the
> proper API (JS_SetPrivate) and tested a DEBUG-compiled version of this
> code, you would have hit an assertion telling you so.
>
> >    return proto;
> >}
> >
> >static JSBool GetOptionProperty (JSContext *cx, JSObject *obj, jsval id,
> >jsval *vp)
> >{
> >  int i = 9;
> >  return JS_TRUE;
> >}
> >
> >
>
> Despite the above small and large problems, you have not shown enough to
> say why the value getter is not being called.  But fix the above first,
> retest, and debug a little -- try breakpointing in js_GetProperty and
> stepping into functions called from it.
>
> /be

.