extended attributes, spotlight and xcode screenshots

If you shall find yourself wondering, as i did, how exactly does Xcode know which device too what screenshot from the ones it manages the answer is simple, it just saves extended attributes for the files with the device id under com.apple.DTDeviceKit.screenshot.device_id e.g.

[valexa@VAiMac:~] $ xattr -l /Volumes/Storage/Screenshots/Screenshot 2010.07.13 01.43.57.png
com.apple.DTDeviceKit.screenshot.device_id: 5a14571ebe34512345b7345e13454a

Finder being finder has no way whatsoever to display or search for extended attributes, however some useful spotlight metadata is saved (the spotlight metadata itself used to be saved as extended com.apple.metadata attributes and xattr is still the only way to edit it) :

[valexa@VAiMac:~] $ mdls /Volumes/Storage/Screenshots/Screenshot 2010.07.13 01.43.57.png
….
kMDItemPixelHeight = 1024
kMDItemPixelWidth = 768
….

This can in fact be searched with finder even if not readily apparent, you have to add a specific Raw Query for it to understand the raw commands that you would have given to mdfind e.g.:

[valexa@VAiMac:~] $ mdfind -onlyin /Volumes/Backup kMDItemIsScreenCapture == 1
/Volumes/Backup/10.8/Screen Shot 2012-03-03 at 12.00.30 AM.png

This searches for screenshots taken from your mac (you can search for specific types for example whole screen ones with kMDItemScreenCaptureType == “display”, screenshots taken of specific windows with kMDItemScreenCaptureType == “window” or “selection” etc)

I had to do this because my screenshots folder contains both the Xcode ones and my mac screenshots, my specific goal was to figure out why some iOS screenshots there no longer showed under their corresponding devices, it turns out that i edited some with Photoshop and it replaced the extended attributes.

Editing those attributes with finder and AppleScript while possible is extremely convulted and employs shell calls anyway so we just head back to Terminal with the newfound knowledge of what screenshots we have.

Now if you only have one device for each screen resolutions available in iOS you are in luck, to print the extended attributes for iPhone, iPhone Retina, iPad, iPad Retina respectively, you can do:

mdfind -onlyin /Volumes/Storage/Screenshots/ “kMDItemPixelWidth == 480 || kMDItemPixelHeight == 480” -0 | xargs -0 xattr -l
mdfind -onlyin /Volumes/Storage/Screenshots/ “kMDItemPixelWidth == 960 || kMDItemPixelHeight == 960” -0 | xargs -0 xattr -l
mdfind -onlyin /Volumes/Storage/Screenshots/ “kMDItemPixelWidth == 768 || kMDItemPixelHeight == 768” -0 | xargs -0 xattr -l
mdfind -onlyin /Volumes/Storage/Screenshots/ “kMDItemPixelWidth == 1536 || kMDItemPixelHeight == 1536” -0 | xargs -0 xattr -l

Now that you seen your device id’s of the screenshots with proper attributes you can go ahead an set the proper id for all screenshots for a screen type e.g.:

mdfind -onlyin /Volumes/Storage/Screenshots/ “kMDItemPixelWidth == 480 || kMDItemPixelHeight == 480” -0 | xargs -0 xattr -w com.apple.DTDeviceKit.screenshot.device_id ‘5a14571ebe34512345b7345e13454a’

Xcode will immediately catch on the change and credit the screenshot properly for it’s source device.

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