Xamarin Binding "Wrapper type '' is missing its native ObjectiveC Class

Question

I am trying to bind an external accessory MSR SDK to Xamarin. Note, this is ON the device. It does not work in the simulator at all. I keep getting this error:

Wrapper type 'iMagProII.IMag' is missing its native ObjectiveC class 'IMag'.

Here is my .cs with my linker flags:

[assembly: LinkWith ("libiMagSDK.a", LinkTarget = LinkTarget.ArmV6 | LinkTarget.ArmV7 | LinkTarget.Simulator, SmartLink = true, ForceLoad = true, IsCxx = true, Frameworks = "CoreGraphics ExternalAccessory", LinkerFlags="-lsqlite3.0 -lc++")]

Here is the Stack Trace:

 at MonoTouch.Registrar.DynamicRegistrar.OnRegisterType (MonoTouch.Registrar.ObjCType type) [0x00334] in /Developer/MonoTouch/Source/monotouch/src/ObjCRuntime/.pmcs-compat.DynamicRegistrar.cs:573 
  at MonoTouch.Registrar.Registrar.RegisterTypeUnsafe (System.Type type, System.Collections.Generic.List`1& exceptions) [0x009a4] in /Developer/MonoTouch/Source/monotouch/src/ObjCRuntime/.pmcs-compat.Registrar.cs:1027 
  at MonoTouch.Registrar.Registrar.RegisterType (System.Type type, System.Collections.Generic.List`1& exceptions) [0x00011] in /Developer/MonoTouch/Source/monotouch/src/ObjCRuntime/.pmcs-compat.Registrar.cs:680 
  at MonoTouch.Registrar.DynamicRegistrar.Register (System.Type type) [0x00002] in /Developer/MonoTouch/Source/monotouch/src/ObjCRuntime/.pmcs-compat.DynamicRegistrar.cs:839 
  at MonoTouch.ObjCRuntime.Class.Register (System.Type type) [0x00000] in /Developer/MonoTouch/Source/monotouch/src/ObjCRuntime/.pmcs-compat.Class.cs:126 
  at MonoTouch.ObjCRuntime.Class.GetHandle (System.Type type) [0x00000] in <filename unknown>:0 
  at MonoTouch.Foundation.NSObject.AllocIfNeeded () [0x00015] in /Developer/MonoTouch/Source/maccore/src/Foundation/.pmcs-compat.NSObject2.cs:390 
  at MonoTouch.Foundation.NSObject..ctor (MonoTouch.Foundation.NSObjectFlag x) [0x00006] in /Developer/MonoTouch/Source/maccore/src/Foundation/.pmcs-compat.NSObject2.cs:102 
  at iMagProII.IMag..ctor () [0x00000] in /Users//Projects/Xamarin/Bindings/Unimag/iMagProII/obj/Debug/ios/iMagProII/IMag.g.cs:112 
  at iMagProII.iOS.ImagViewController.ViewDidLoad () [0x0005c] in /Users//Projects/Xamarin/Bindings/Unimag/iMagProII.iOS/ImagViewController.cs:46 
  at (wrapper managed-to-native) MonoTouch.ObjCRuntime.Messaging:IntPtr_objc_msgSendSuper (intptr,intptr)
  at MonoTouch.UIKit.UIViewController.get_View () [0x00030] in /Developer/MonoTouch/Source/monotouch/src/build/compat/UIKit/.pmcs-compat.UIViewController.g.cs:2232 
  at iMagProII.iOS.ImagViewController..ctor () [0x00008] in /Users//Projects/Xamarin/Bindings/Unimag/iMagProII.iOS/ImagViewController.cs:23 
  at iMagProII.iOS.AppDelegate.FinishedLaunching (MonoTouch.UIKit.UIApplication app, MonoTouch.Foundation.NSDictionary options) [0x00016] in /Users//Projects/Xamarin/Bindings/Unimag/iMagProII.iOS/AppDelegate.cs:33 
  at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
  at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/.pmcs-compat.UIApplication.cs:38 
  at iMagProII.iOS.Application.Main (System.String[] args) [0x00008] in /Users//Projects/Xamarin/Bindings/Unimag/iMagProII.iOS/Main.cs:17

Any help on getting this library bound would be greatly appreciated. I have been banging my head at it for hours now.

score 8 · Accepted Answer · answered Jun 19 '14 at 21:51

This occurs when the class IMag can't be found in the final executable.

The most common reasons for this are:

A typo in the class name.
The native library does not include the architecture you're building for. For instance the native library needs to contain i386 code to run in the simulator. You can use the lipo tool to list the architectures in the native library:
```
$ lipo -info /path/to/libiMagSDK.a
```
You also need to know the architecture you're using for the app, you can check this in the project's iOS Build settings, on the Advanced page. Select one that the native library includes.
The native library in the binding project depends on another native library which is not in the binding project (and the IMag class is in that other library). All non-platform dependencies must be included.
The native library is incorrectly built, and doesn't include the class you're trying to bind (this is not frequent, but I've still seen it several times). You can use the nm tool to check what's included in a native library:
```
$ nm -arch armv7 /path/to/libiMagSDK.a | grep IMag
0x0000f00d S _OBJC_CLASS_$_IMag
[other results]
```
The above result would indicate that the class is included in the native library.

This works perfectly. I never found good documentation on how to find out what architecture the static library was build off of. Thank you! — Tripadelphia, Jun 20 '14 at 12:05

Xamarin Binding "Wrapper type '' is missing its native ObjectiveC Class

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