Duplicate Symbols for Architecture arm64

When I try running my Xcode Project it fails with an error stating that I have duplicate symbols. I looked online where the find these duplicates but have had no luck:

![enter image description here][1]


[1]:

Any ideas how to fix this?

From the errors, it would appear that the FacebookSDK.framework already includes the Bolts.framework classes. Try removing the additional Bolts.framework from the project.

Well,
some times when using SDK like FB or Libraries like Vuforia or GoogleAnalytics , adding sample projects may cause the problem that they're already including Frameworks and like so ,so you must make sure not repeating symbols you add manually while they're already included in samples

For me it helped to switch the "No Common Blocks" compiler setting to NO:
It pretty much seems to make sense, the setting is explained here:

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This error happens when Linker is trying to link the obj files. Few reasons that i could think of for this error are:

1. The duplicated Function/Class is defined at two different places/files in the project and only one of them was supposed to compile for any variation of build command. But somehow both those files got compiled in your project. So you need to check your if-else conditions or other dependencies which adds src files to the list of files needed to be compiled and remove the un-needed file for your particular build command.

2. The duplicated Function/Class is defined accidentally at two different places/files in the project. Remove the wrong definition.

3. Clean your OBJ directory before you build again, there could be some old obj files in there from your previous builds which might be causing this conflict.

P.S i am no expert, but this is how i solved this problem when i faced it. :)

From the errors, it would appear any Classes appear multiple time.Find and removed that Classes it will working.

Am creating AppDelegate.h and .m file creating multiple time. So this error will occur.Finally find and removed that classes it's working fine for me.

For me it was that i imported a file as a .m not a .h by mistake

On upgrading to Xcode 8, I got a message to upgrade to recommended settings. I accepted and everything was updated.
I started getting compile time issue :

Duplicate symbol for XXXX
Duplicate symbol for XXXX
Duplicate symbol for XXXX

A total of 143 errors.
Went to Target->Build settings -> No Common Blocks -> Set it to NO.
This resolved the issue. The issue was that the integrated projects had code blocks in common and hence was not able to compile it. Explanation can be found [here][1].


[1]:

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For me, the issue was the style of creation of const, that worked fine until this iOS8.. i had a few lines as:

int const kView_LayoutCount = 3;

in my .h file. Six lines like resulted in 636 linker files once common blocks was set to NO. (14k+ if YES). Moved the lines to .m after stripping .h of the value declaration and compilation was good to go.

Hope this helps others!

If you are moving to Xcode 7 or 8 and are opening a really old project, I've encountered this problem:

in `SomeConstFile.h`

NSString * const kAConstant;


in `SomeConstFile.m`

NSString *const kAConstant = @"a constant";

Earlier versions of the compiler assumed that the definition in the header file was extern and so including SomeConstFile.h all over the place was fine.

Now you need to explicitly declare these consts as extern:

in `SomeConstFile.h`

extern NSString * const kAConstant;