State Change Monitoring

Question

I would like to know if there are any apple Xcode APIs for monitoring state changes before I attempt to build my own. The app I work on changes out several View Controllers. Each controller can have a couple smaller custom views plus the usual check boxes, text fields etc.

The main app needs to know if a view controller or anything on it is edited from its previous state when it is pulled up before it is saved again. We only need to know if the state has changed. The caveat is this: if a user checks a checkbox , that is considered a change of state, but if the user also unchecks the check box, then the state is not changed.

I was looking at the NSUndoManager but I'm nor sure if it will work. Any suggestions appreciated

Answer 1

There are a couple of approaches:

1. Implement a centralized "model" object. In this scenario, view controllers would just update properties of this main model object and there's little else you have to do. View controllers would then, in viewDidAppear, check the state of this model object and see if anything changed and act accordingly.

2. Another approach would be to implement a delegate-protocol pattern, by which the various controllers might have some delegate property that would indicate what object must be informed of data changes. This object that would be the data delegate would be defined to conform to some well defined protocol that indicate how to inform it of the changes.

3. If, though, you (a) have multiple objects that need to be informed of changes; and/or (b) these changes might happen asynchronously while a view is presented, you need some mechanism to do this notification. The two common approaches would be either with key-value-observing of that model object or by posting a custom notification to the NSNotificationCenter.

To advise you better, we'd need a better sense of the nature of your model object, whether updates are happening asynchronously in the background, etc.