MT5202 Native linking failed Undefined symbols for architecture armv7: - xamarin.ios

Question

I have been having this issue for a number of days now, and have been unable to make any headway on it.
I have a native Obj-C library that i am trying to bind using a MonoTouch binding project. The binding Dll is created, but when i import it to an app and try to compile I get a MT5202 Native linking failed error.
Reading the build output shows that the symbols for the iOS version i am compiling for are missing.
Undefined symbols for architecture armv7:
with the build output showing a number of linking issues (only a few shown)
"_CVPixelBufferGetPixelFormatType", referenced from:
-[DecodePickerController captureOutput:didOutputSampleBuffer:fromConnection:] in libQuickMarkSDK.a(DecodePickerController.o)
-[QMImageUtil saveToAlbum:] in libQuickMarkSDK.a(QMImageUtil.o)
"_CVPixelBufferGetPlaneCount", referenced from:
+[QMImageUtil imageBufferSave:f:] in libQuickMarkSDK.a(QMImageUtil.o)
+[QMImageUtil imageBuffer:zoom:w:h:f:] in libQuickMarkSDK.a(QMImageUtil.o)
"_CVPixelBufferGetWidth", referenced from:
-[DecodePickerController captureOutput:didOutputSampleBuffer:fromConnection:] in libQuickMarkSDK.a(DecodePickerController.o)
-[QMImageUtil saveToAlbum:] in libQuickMarkSDK.a(QMImageUtil.o)
"_CVPixelBufferGetWidthOfPlane", referenced from:
+[QMImageUtil imageBufferSave:f:] in libQuickMarkSDK.a(QMImageUtil.o)
"_CVPixelBufferLockBaseAddress", referenced from:
-[DecodePickerController captureOutput:didOutputSampleBuffer:fromConnection:] in libQuickMarkSDK.a(DecodePickerController.o)
"_OBJC_CLASS_$_AVCaptureDevice", referenced from:
objc-class-ref in libQuickMarkSDK.a(QuickMarkCameraUtil.o)
"_OBJC_CLASS_$_AVCaptureDeviceInput", referenced from:
objc-class-ref in libQuickMarkSDK.a(QuickMarkCameraUtil.o)
To begin with I thought it was just an error with the bindings. So I rebuilt the bindings. No joy. So to test a theory I tried to use the RedLaser mono bindings available from github. This also provided the same error. (if -unsafe is removed from the makefile).
the linkwith statement for the library I need to bind is
assembly: LinkWith ("libQuickMarkSDK.a", LinkTarget.ArmV7, ForceLoad = true, Frameworks = "AVFoundation CFNetwork CoreMedia CoreVideo libz.1.2.5.dylib MobileCoreServices QuartzCore Foundation SystemConfiguration")]
and the Monotouch addition flags being used is -cxx
I have read alot of the other issues but nothing has helped to solve the issue, any help would be great.

Answer 1

You did not state any version numbers (iOS, Xcode, MonoTouch...) so it's a bit hard to give a specific/definitive answer.
That situation can happens when you update a project to iOS6 / Xcode 4.5 where support for ARMv6 was removed. If your native libraries only included ARMv6 then they (the native library, not the binding project) will need to be recompiled for ARMv7 (since it's now a requirement).
To check this please try doing (include the full path to your native library):
file libQuickMarkSDK.a
That should tell you the architectures that your native library supports. Those needs to match the LinkTarget you provide in your binding project (otherwise you'll get errors from the native linker).

Answer 2

Did you try poupou's suggestion in his last comment? I had the same error when compiling for iPhone but not for Simulator. I found that it was a number of missing Frameworks in the LinkWith section. To work out which Frameworks were missing, I googled (for example) CVPixelBufferGetWidthOfPlane Framework.
Credit for this answer goes to cheeesus: MonoTouch Build: ld: symbol(s) not found for architecture armv7