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iphoneiosprotocolskey-value-observingnsnotifications

KVO vs NSNotification vs protocol/delegates?

I have some idea of which to use when but the exact usage is still not clear to me. Can someone explain with example?

Solution

  • Use a delegate if you want to talk to only one object. For example, a tableView has a delegate - only one object should be responsible for dealing with it.

    Use notifications if you want to tell everyone that something has happened. For example in low memory situations a notification is sent telling your app that there has been a memory warning. Because lots of objects in your app might want to lower their memory usage it's a notification.

    I don't think KVO is a good idea at all and try not to use it but, if you want to find out if a property has changed you can listen for changes.

    Hope that helps.

    PS This sums up why I think KVO is broken