Backwards compatibility when using Core Data

Question

Could anybody shed some light as to why is my app crashing with the following error on iPhone OS 2.2.1

dyld: Symbol not found: _OBJC_CLASS_$_NSPredicate
  Referenced from: /var/mobile/Applications/456F243F-468A-4969-9BB7-A4DF993AE89C/AppName.app/AppName
  Expected in: /System/Library/Frameworks/Foundation.framework/Foundation

I have weak linked CoreData.framework, and have the Base SDK set to 3.0 and Deployment Target set to SDK 2.2

The app already uses other 3.0 features when available and I did not have any problems with those. But apparently the backward-compatibility methods used for other features do not work with Core Data.

The app crashes before app delegate's applicationDidFinishLaunching gets called.

Here's the debugger log:

[Session started at 2010-05-25 20:17:03 -0400.]
GNU gdb 6.3.50-20050815 (Apple version gdb-1119) (Thu May 14 05:35:37 UTC 2009)
Copyright 2004 Free Software Foundation, Inc.
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There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "--host=i386-apple-darwin --target=arm-apple-darwin".tty /dev/ttys001
Loading program into debugger…
sharedlibrary apply-load-rules all
warning: Unable to read symbols from "MessageUI" (not yet mapped into memory).
warning: Unable to read symbols from "CoreData" (not yet mapped into memory).
Program loaded.
target remote-mobile /tmp/.XcodeGDBRemote-12038-42
Switching to remote-macosx protocol
mem 0x1000 0x3fffffff cache
mem 0x40000000 0xffffffff none
mem 0x00000000 0x0fff none
run
Running…
[Switching to thread 10755]
[Switching to thread 10755]
Re-enabling shared library breakpoint 1
Re-enabling shared library breakpoint 2
Re-enabling shared library breakpoint 3
Re-enabling shared library breakpoint 4
Re-enabling shared library breakpoint 5
(gdb) continue
warning: Unable to read symbols for ""/Users/alex/iPhone Projects/AppName/build/Debug-iphoneos"/AppName.app/AppName" (file not found).
dyld: Symbol not found: _OBJC_CLASS_$_NSPredicate
  Referenced from: /var/mobile/Applications/456F243F-468A-4969-9BB7-A4DF993AE89C/AppName.app/AppName
  Expected in: /System/Library/Frameworks/Foundation.framework/Foundation

(gdb) 

Answer 1

Sorry, just re-read your question.. It looks like the framework itself can't be weakly linked. I guess it means you can't have a 2.x target with Core Data framework :(

i.e. the whole framework is not available on the target platform, and weak linking does not apply.

Answer 2

Apparently you can't reference NSPredicate by a literal class symbol if you won't to have backwards compatibility with iPhone OS 2.2

So changed my reference to NSPredicate to:

[fetchRequest setPredicate:[NSClassFromString(@"NSPredicate") predicateWithFormat:@"EntryId == %@", [NSNumber numberWithInt: index]]];

and it works now.

See https://devforums.apple.com/message/225591#225591