UXNotificationObs

UXNotificationObs is one registration inside a UXNotificationCenter. You do not construct one; addObserver makes it. The centre’s lifetime guarantees are implemented here.

#use <UXKit>            // or #import "UXNotificationCenter.xc"

Overview

class UXNotificationObs {
    weak: Object*  observer;      // identity, for removeObserver
    callback method void(UXNotification* note);
    u8*            name;          // 0 = match ANY name
    weak: Object*  object;        // 0 = match ANY sender
}

It has four fields, and three of them avoid owning anything.

Why both references are weak

observer is weak because the centre must not keep a subscriber alive: window → centre → observer → window would be a retain cycle around every window in the program.

object, the sender being filtered on, is weak for the same reason: an observer watching one document should not keep that document in memory.

method is a callback, which never owns its receiver.

A registration therefore holds nothing alive. When an observer dies its callback reads false, dispatch skips the entry, and the next sweep prunes it. For this reason removeObserver is hygiene rather than a crash guard.

The two wildcards

Both name and object treat 0 as match anything:

field	`0` means
`name`	every notification, whatever it is called
`object`	every sender

object == 0 is the common case: “tell me about doc.changed from anyone”.

name == 0 is rarer. A registration with no name hears everything, which suits a logger or a debugging trace. The addObserver signature takes a name, so pass 0 explicitly:

nc.addObserver((Object*)tracer, &tracer.onAny, (u8*)0, (Object*)0);

Both wildcards at once means “every notification from every sender”. It is cheap to write and expensive to leave in, since it fires on every post in the process.

Names are compared by content

The centre compares notification names byte by byte, not by pointer. Two copies of the same string match, so a name read from a file, built at run time, or defined in a different compilation unit still works.

With interned pointers instead, "doc.changed" from two places would fail to match without any error.

Fields

observer

weak: Object* observer

Identity only. removeObserver matches on it; the centre never calls it directly.

method

callback method void(UXNotification* note)

What gets called. It carries its receiver, so the observer field is not used for dispatch.

name

u8* name        // 0 = any

object

weak: Object* object    // 0 = any sender