Friday, June 3, 2011

Usability Blooper: The operation can't be completed in Mac OS X copying

Here's a blooper in Mac OS X that has driven me crazy for several years.

The following 'copy failure' modal dialog can occur when trying to copy a large collection of files from one place to another using Finder. The dialog states: "The operation can't be completed because you don't have permission to access <file> - OK".

This breaks several key usability guidelines for the design of error messages:
  1. It doesn't give the user sufficient information to readily solve the problem: The user might not recognize the file, or know in which folder it is stored. There should be an option to open the enclosing folder so the user can look at the file and fix the permissions.
  2. It leaves the user half way through a incomplete task. There should be an option to continue to copy all other files. After the whole copying task is complete, information about which files were not copied should then be displayed, with the options to ignore each or to open its enclosing folder as in my point 1. Ideally, there also ought also be the option to revert to the state before the copying started (i.e. undo the entire copy process)
Here is a scenario in which it occurs for me: I like to back up my Mac OS X files in various different ways. Sometimes I copy my entire 'Library' folder to a backup location. The above error occurs in the middle of the process (the problem is with a particular Real Networks file that I actually don't care about). Interestingly enough, Spotlight hasn't even indexed this file (probably because of the same permission problems) so I am not able to locate it straightforwardly.

There is a workaround, but it is annoying. I look in the destination to see how much of the copying has been completed. Luckily copying proceeds alphabetically by file name, so I can then just initiate new copies to finish off copying the top level folder, and each level of subfolder, skipping the problem file. This workaround is not, however, something I would want to inflict on the non-expert. And it becomes very tricky when more than one file fails to be copied.

Other workarounds are to use tools other than the Finder for backup, and indeed I do that too. However, my inclination is to back up in a variety of ways in case one method fails.

These workarounds won't work in some contexts. For example,
  • If you have command-clicked on an arbitrary set of files and folders and have dragged them all to a destination, when the copying task fails you might have already lost track of  which items you carefully selected to copy.
  • If you initiate many copy operations, having them all proceed concurrently, when one or more of them fail in the above manner, you may be completely at a loss to know what parts of your work have been completed, and which have not been completed. Ideally then, the 'copy failure' dialog should also give you information about the complete set of files being copied, and allow you to resume or complete the process after fixing the permissions.

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