Core Animation Bindings

In Core Animation, CALayers are live : they're created and stay here until they're destroyed, just like DOM nodes in an html page. This is in contrast to Cocoa drawing, or the canvas html tag, where drawing is done programmatically when needed. So when using CALayers to display data, we need to match source objects and CALayers.

Image:Core Animation Bindings.jpg

Just a hash

We use a custom view CAListView and observe data in an NSArrayController. To update the view, we need to know when to create / delete layers and when to update them to reflect their source object.

  • creating/deleting layers observe changes by binding to arrayController.arrangedObjects — this will tell us when objects are created, moved, and deleted. Use a NSMutableDictionary to store the CALayers, using their source object's pointer as a key. To know when to create CALayers, loop through the objects array and query the NSMutableDictionary for an existing CALayer. If not found, create a new one. To know when to delete CALayers, loop through the NSMutableDictionary and check if its keys (pointers to objects) are still in the objects array. If not, delete them.
  • updating layers bind once more with bastard observing to observe all the keys of all the controller's objects. When an object changes, query the NSMutableDictionary for knowing which CALayer to update. (if it's a CATextLayer, update it withlayer.string = [observedObject name], if it's a color change, with layer.backgroundColor = …, etc.)

Sample code

Image:iconZip.png Core Animation

Core Animation

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