Re: Core Data, NSImageView, and Thumbnailing

FROM : Diederik Hoogenboom
DATE : Wed Aug 30 17:27:55 2006

David,

While we are pointing in directions...

If 10.4 only compatibility is no issue you can use

CGImageRef image = CGImageSourceCreateThumbnailAtIndex(imageSource,
0,thumbnailDictionary);

to create the thumbnail.


Diederik

On 26-aug-2006, at 0:55, David Rocamora wrote:

> Thanks Chris! I think your thorough message will point me in the right
> direction. I appreciate your response.
>
> -David
>
>
> On 8/25/06 6:52 PM, "Chris Hanson" <<email_removed>> wrote:
>

>> "How do I generate a thumbnail from an image?" really isn't a Core
>> Data question; the fact that you're using Core Data isn't really
>> relevant to it.  However, there is a Core Data question lurking in
>> the above once you figure out how to generate a thumbnail:  How do
>> you manage both an "image" attribute and a "thumbnail" attribute
>> where the thumbnail is the only one you want to save?
>>
>> That has a fairly straightforward answer.  Your image attribute
>> should be marked transient in your data model.  Either when your
>> image is set, or when your managed object instance is saved, you
>> should generate a thumbnail from the image and assign it to the
>> thumbnail attribute.  And either when your image is accessed, or when
>> your managed object instance is awakened from a fetch, you should
>> return your thumbnail data instead.
>>
>> What you're really doing here is using the thumbnail persistent
>> attribute as a backing store for the image transient attribute.  How
>> to follow this pattern in the general case is described in the Core
>> Data documentation; this is just a specific case.  Other similar
>> cases might be to have an NSURL as an attribute or an attribute
>> representing a reference to a file.[1]
>>
>> Another interface-centric possibility -- which may be a lot easier,
>> depending on your needs -- might be to write your own value
>> transformer to apply to the NSImageView's data binding.  When
>> transforming from the image view's NSImage to an NSData, your value
>> transformer could also turn the image into a thumbnail if it's too
>> large.
>>
>>    -- Chris

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