问题
I have error "Cocoa error 256" when I try to save data. How to fix it? And what problem?
回答1:
According to the help reference in Xcode:
NSFileReadUnknownError Read error, reason unknown
Available in Mac OS X v10.4 and later.
Declared in FoundationErrors.h.
Sadly, that's probably not too helpful, though it is an unknown -read- error.
回答2:
If its a core data error there is probably an actual error object somewhere near where the error occurs. If you dump the error objects userInfo dictionary, you can usually get a lot more detail than just the error code itself.
回答3:
This is what it boils down to (as Tegeril said)
NSFileReadUnknownError Read error, reason unknown
Available in Mac OS X v10.4 and later.
Declared in FoundationErrors.h.
A file can also be a resource located at a URL/URI, if the URL has unencoded characters it can cause this type of error.
Check the path to the resource/file.
回答4:
I ran into exactly this error when populating an SQLite database for an iOS app using a custom script (ie not using Core Data). It turns out that there is some metadata which you have to update yourself, after adding new rows. Find the row in Z_PRIMARYKEY where Z_NAME equals the name of the table you've just inserted into. Make sure that Z_MAX in this row is equal to the highest value of Z_PK in the table you've inserted the rows into. In my case, as soon as I updated Z_MAX with the correct number, the error went away.
So, for the "ZAUTHOR" table:
SELECT z_pk FROM ZAUTHOR ORDER BY z_pk DESC LIMIT 1; /* Returns 1234 */
UPDATE Z_PRIMARYKEY SET z_max = 1234 WHERE z_name = 'Author';
This is the article which helped me track down the error.
回答5:
I get this error on Xcode 6 (& 7) when switching a network connection while the Simulator is open. For example moving from one wireless network to another. The solution for me is to Quit Simulator and restart.
来源：https://stackoverflow.com/questions/1915478/cocoa-error-256-core-data