nsIPrefBranch observers Topic is solved

[yami_]

If I understand documentation correctly, to use nsIPrefBranch observer you need to:

• Add the observer:

  Code: Select all

  let prefs = Components.classes["@mozilla.org/preferences-service;1"]
  	.getService(Components.interfaces.nsIPrefService)
  	.getBranch("extensions.yami.preftest.");
  prefs.addObserver("", yami.preftest, false);
  

• Point it to an object with observe method:

  Code: Select all

  yami.preftest = {
  	observe: function observe(sub, topic, data) {
  		if(topic == "nsPref:changed") {
  			/* ... */
  		}
  		return;
  	},
  }
  

For me this works, but is not reliable - it will randomly stop working. I am able to reproduce this on Pale Moon and Basilisk using the attached preftest extension and following steps:

1. Install preftest
2. Open add-on manager
3. Open preftest's options page
4. Restart the browser (File > Restart...)
5. After the browser restarts, quickly try to change drop-down menu's selection
6. "Observer execution counter" should increment
7. Open a new tab
8. While on that tab, navigate to any webpage
9. Switch to the add-on manager's/preftest's options tab
10. Try to change drop-down menu's selection again

Now the "Observer execution counter" will not increment.
Does anyone have any idea why this is not working correctly?

[JustOff]

This is because you declared prefs as a local variable, so js garbage collector kills it. You need something like this:

Code: Select all

	init: function init(e /* object */) /* void */ {
		yami.prefs = Components.classes["@mozilla.org/preferences-service;1"]
			.getService(Components.interfaces.nsIPrefService)
			.getBranch("extensions.yami.preftest.");
		yami.prefs.addObserver("", yami.preftest, false);
	},

[yami_]

This is because you declared prefs as a local variable, so js garbage collector kills it.

Thanks JustOff, now it works correctly.