Question

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KVO and NSMutableArray

Like the title says, I need to be able to detect a change in a mutable array. The reason for this would be to automatically refresh my mapview for an app I’m making as soon as the user adds a new location.

I imagine it would be something like asking if the array is equal to the array’s count plus one or the array’s count minus one but I don’t know how to implement that.

If you need more information before answering please don’t hesitate to ask in the comments.

Answer 1

You can use Key-Value Observing for this. For more details check Introduction to Key-Value Observing Programming Guide.

Key-value observing provides a mechanism that allows objects to be
notified of changes to specific properties of other objects. It is
particularly useful for communication between model and controller
layers in an application. (In OS X, the controller layer binding
technology relies heavily on key-value observing.) A controller object
typically observes properties of model objects, and a view object
observes properties of model objects through a controller. In
addition, however, a model object may observe other model objects
(usually to determine when a dependent value changes) or even itself
(again to determine when a dependent value changes).

You can observe properties including simple attributes, to-one
relationships, and to-many relationships. Observers of to-many
relationships are informed of the type of change made—as well as which
objects are involved in the change.

Check this blog about KVO on how to use it. Also check this tutorial. Check this question as well, Key-Value-Observing a to-many relationship in Cocoa