My first attempt at providing table thumbnails was to load an NSMutableArray with all the images that the user has selected when the plugin starts. Unfortunately there can be a significant delay while they are retrieved from Aperture: above a few hundred the delay becomes irritating. Once the data was in my array, access was fast and the table scrolled up and down smoothly.

To improve start-up performance I replaced my array ivar imageTable with two methods: -countOfImageTableData and -objectInImageTableDataAtIndex:. Now, through the magic of KVC the array controller instantiated in the nib will access these two methods instead of the array. In fact it was trying to do that all along, failing, and falling back to accessing the ivar directly. The idea is that by generating the data on demand, the start-up performance problem will go away and the time taken distributed across all the images as they are viewed in the table.

Here is the code for the first method:

The check for the API version exists because my code simply does not support it. There used to be a less efficient way to retrieve thumbnails that I have no intention of coding. The result of this is that the image table is blank if an old API is detected. I also log a message to that effect on initialization, so it is not a complete mystery to the user.

The second method is very simple:

The code for -textForImageAtIndex: and -thumbnailForImageAtIndex: is not simple, however. But it is straight forward. The text code gets the properties of the image from Aperture and formats it appropriately. The thumbnail code is much easier to follow:

Master images (and potentially any image) don't have thumbnails, so I have to substitute. I do that with a small TIFF image that I put into the plugin bundle that says "No Image".

How did I do? Start-up was fast, even for thousands of images, so that problem was fixed. But there were other problems. Scrolling was dog slow. Logging showed that -countOfImageTableData and -objectInImageTableDataAtIndex: were being called for practically every pixel of scrolling I was doing, retrieving the image and generating the text each time. Horrible.

So the next step was to implement caching: retaining the images and text in memory and delivering those instead of getting them from Aperture each time they are needed.

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

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