volker böhm

i need my object to be notified when one of its attributes changes.

this seems to work fine if i write custom getter and setter methods, 

however it's a little overkill in the simple example i'm working on.

so i tried the "notify" message, cause the doc says:

"As an alternative to writing a custom setter, you can take advantage 

of the fact that objects receive a "notify" message whenever one of 

the example below compiles fine, but i can't get any notification 

when changing the "test" attribute in max.

void *myObj_new(t_symbol *s, long argc, t_atom *argv);

t_max_err myObj_notify(t_myObj *x, t_symbol *s, t_symbol *msg, void 

    c = class_new("testnotify", (method)myObj_new, 0, sizeof(t_myObj), 

    class_addmethod(c, (method)myObj_bang, "bang", 0);

    class_addmethod(c, (method)myObj_int, "int", A_LONG, 0);

    class_addmethod(c, (method)myObj_notify, "notify", A_CANT, 0);

    CLASS_ATTR_LONG( c, "test", 0, t_myObj, testattr );

    //object_post((t_object *)x, "i got msg: %s", msg->s_name);

    if(msg == gensym("attr_modified")) {

        attrname = (t_symbol *)object_method((t_object *)data, gensym 

        object_post((t_object *)x, "i got a %s notification from the %s 

attribute", msg->s_name, attrname->s_name);

void *myObj_new(t_symbol *s, long argc, t_atom *argv)

    t_myObj *x = (t_myObj *)object_alloc(s_myObj_class);

i need my object to be notified when one of its attributes changes.
this seems to work fine if i write custom getter and setter methods,  
however it's a little overkill in the simple example i'm working on.

so i tried the "notify" message, cause the doc says:
"As an alternative to writing a custom setter, you can take advantage  
of the fact that objects receive a "notify" message whenever one of  
their attributes is changed."

the example below compiles fine, but i can't get any notification  
when changing the "test" attribute in max.
what am i doing wrong?

typedef struct _myObj
{
	t_object	ob;
	long	testattr;
} t_myObj;

void myObj_bang(t_myObj *x);
void myObj_int(t_myObj *x, long n);
void *myObj_new(t_symbol *s,  long argc, t_atom *argv);
t_max_err myObj_notify(t_myObj *x, t_symbol *s, t_symbol *msg, void  
*sender, void *data);

int main(void)
{
	t_class *c;
	c = class_new("testnotify", (method)myObj_new, 0, sizeof(t_myObj),  
0L, A_GIMME, 0);

	class_addmethod(c, (method)myObj_bang, "bang", 0);
	class_addmethod(c, (method)myObj_int, "int", A_LONG, 0);
	class_addmethod(c, (method)myObj_notify, "notify", A_CANT, 0);

	// attributes
	CLASS_ATTR_LONG( c, "test", 0, t_myObj, testattr );

	class_register(CLASS_BOX, c);
	s_myObj_class = c;
	return 0;
}

t_max_err myObj_notify(t_myObj *x, t_symbol *s, t_symbol *msg, void  
*sender, void *data) {
	 // look for all messages
	post("notify");
	//object_post((t_object *)x, "i got msg: %s", msg->s_name);

	t_symbol *attrname;
	if(msg == gensym("attr_modified")) {
		attrname = (t_symbol *)object_method((t_object *)data, gensym 
("getname"));
		object_post((t_object *)x, "i got a %s notification from the %s  
attribute", msg->s_name, attrname->s_name);
	}
	return 0;
}

void myObj_bang(t_myObj *x) {
	post("test: %ld", x->testattr);
}

void myObj_int(t_myObj *x, long n) {
	x->testattr = n;
}

void *myObj_new(t_symbol *s,  long argc, t_atom *argv)
{
	t_myObj *x = (t_myObj *)object_alloc(s_myObj_class);
	x->testattr = 77;
	return (x);
}


notify-when-attribute-changes

You need to attach the object to itself (ensuring that it gets registered) in order to receive attr notifications from itself:

object_attach_byptr_register(x, x, CLASS_BOX);

On 29 Nov 2008, at 15:00, Jeremy Bernstein wrote:

> You need to attach the object to itself (ensuring that it gets 

> registered) in order to receive attr notifications from itself:

> object_attach_byptr_register(x, x, CLASS_BOX);

might be an idea to add this line to the documentation in "Sending 

On 29 Nov 2008, at 15:00, Jeremy Bernstein wrote:
>
> You need to attach the object to itself (ensuring that it gets  
> registered) in order to receive attr notifications from itself:
>
> in myObject_new():
>
> object_attach_byptr_register(x, x, CLASS_BOX);
>

ah, thanks jeremy, now it works.
might be an idea to add this line to the documentation in "Sending  
Messages, Calling Methods".
maybe it's already somewhere else.

This is very old, but I agree this should really be documented in that particular section of the API, it's still not!

Yes I spend all the afternoon looking what was wrong with my code, reading 10 times the **** manual...

So where could we send PR to update this API documentation ?

Yes I spend all the afternoon looking what was wrong with my code, reading 10 times the **** manual...
So where could we send PR to update this API documentation ?

another vote here to please update the API/SDK documentation - especially around Attributes :)

from the API doc (in the "Sending Messages, Calling Methods" section):

(more documentation on this is coming soon!)

@Antoine: Pull Requests can be made at https://github.com/cycling74/max-sdk 

notify when attribute changes