A problem that I encountered along the way as I implemented my cache was that any change to the data always caused the array controller to load all the elements. This was exactly what I was trying to avoid with a cache, yet it was happening.

After much hair-pulling (and posting to Apple's Cocoa mailing list) I figured that the array controller believed that my array (implemented by methods in my Random_Wok class) was immutable, and therefore any observed change must mean that the entire array had changed and so need a reload. The fix was to make the array controller believe that the array was mutable. To do this I added three more methods:

These are the mutable array methods. I didn't even have to write any code for them because they are never called. They are just there so that the array controller knows that my array is mutable and so will allow updates to individual elements.

Another problem I found that was while the Page Up and Page Down keys worked on the NSTableView, the Home and End keys did not. A little odd. To fix this I subclassed NSTableView and overrode -keyDown:.

I created a custom class called BTKeydownTableView and told Interface Builder to use it instead of NSTableView. Here is the interface:

The implementation is very simple. I read the first character from the event queue and act on it:

To scroll the window to the right place I tell the view to scroll to the first or last rows, as required.

The other parts of this series can be found via the Cocoa page.

Tags: Aperture, Plug-ins, Caching, Cocoa, Random Wok, NSTableView

Retrieving the thumbnail image and generating the text for the table is time-consuming and called very often by the array controller that is controlling the table of images. This results in very slow scrolling of my table. To solve this problem, I added caching; the idea being that repeated requests for the same data come out of memory and do so quickly.

Adding caching was relatively simple, at least to implement simply. Here is the code:

The cache needs a key to cache on. For this I turn the index number into a string and use that as the key. The cache itself is a mutable dictionary that holds dictionaries:

This stores the data I get from Aperture fine and the interface is fast again. But now I have another problem. When the random file name parameters are changed, the cached data becomes stale. So each time a change occurs, I must update the cached text:

And the cached images:

This code enumerates through the cached data replacing the cached text and thumbnail objects. Bindings take care of the table updates. -updateCachedFilenames is called whenever anything changes that could affect the file name, such as a change of alpha case:

-updateCachedImages is called when the type of image changes:

This all works well, and is how Random Wok 1.0 was released. But it still has a problem. The cache grows forever, eating memory as it goes. And as the cache grows, the time taken to update the cached data grows. What is really needed is a cache that throws away the oldest entry once it reaches a certain limit and more data is added. So that is what I implemented next.

The other parts of this series can be found via the Cocoa page.

Tags: Aperture, Plug-ins, Random Wok, NSTableView, Caching, Cocoa