duplicate interface declaration for class 'test_coredataAppDelegate'

Solution 1:

There are two possibilities:

• you have two interfaces with the same name. Use Xcode's find in project menu option to find instances of test_coredataAppDelegate. Then rename one of the interfaces
• somehow you have managed to import the .h file twice. Check to make sure you always use #import and not #include.

Edit:

A bit more info on #import/#include:

#include blindly includes the file at the location of the #include statement. This means that if you #include a file twice in your .m you will get two copies of the file. Almost all traditional C #include files have something like the following bracketing all the content:

// some_file.h
#if !defined SOME_FILE_H
#define SOME_FILE_H

//  entire content of #include file

#endif

The above is sometimes referred to as an include guard macro.

In Objective-C, if you #import a file, a check is performed by the compiler to make sure it has not already been imported. Consequently the guards are usually omitted. So if you #include a file that was supposed to be #imported, neither check will be done and you will sometimes get duplicate definitions.

Solution 2:

This happen because you have a copy of that resource in your finder. It is not necessary had added it in your project. You should find in your finder the files with the same name and delete the files duplicated.