Bug 1524 - set a StructLayout attribute to use Class with external code
Summary: set a StructLayout attribute to use Class with external code
Status: RESOLVED ANSWERED
Alias: None
Product: Xamarin.Mac
Classification: Desktop
Component: Library (Xamarin.Mac.dll) ()
Version: Master
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: 2.0.x
Assignee: Chris Hamons
URL:
Depends on:
Blocks:
 
Reported: 2011-10-16 20:34 UTC by Vittorio G.
Modified: 2015-02-24 12:16 UTC (History)
3 users (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED ANSWERED

Description Vittorio G. 2011-10-16 20:34:51 UTC
Hello, I am trying to implement MethodSwizzling as described here: http://lapcatsoftware.com/blog/2007/11/25/working-without-a-nib-part-6-working-without-a-xib/
It's great to see that all the objc runtime type are already present in monomac, however, after porting the sample code to c# i get an exception:

System.Runtime.InteropServices.MarshalDirectiveException has been thrown
Type MonoMac.ObjCRuntime.Class which is passed to unmanaged code must have a StructLayout attribute.

Here is the code that i wrote that triggers the exception:

        [DllImport("/usr/lib/libobjc.dylib")]
        public static extern System.Reflection.MethodBase class_getClassMethod(Class aClass, Selector aSelector);
        [DllImport("/usr/lib/libobjc.dylib")]
        public static extern void method_exchangeImplementations(System.Reflection.MethodBase a, System.Reflection.MethodBase b);
        private static void Main (string[] args)
        {
            Class bundleClass = new Class("NSBundle");
            System.Reflection.MethodBase originalMethod = class_getClassMethod(bundleClass, new Selector("loadNibNamed:owner:"));
            System.Reflection.MethodBase categoryMethod = class_getClassMethod(bundleClass, new Selector("fake_loadNibNamed:owner:"));
            method_exchangeImplementations(originalMethod, categoryMethod);
        ...

The exception is triggere from the first class_getClassMethod call.
Comment 1 Zoltan Varga 2011-10-21 04:58:37 UTC
-> monomac.
Comment 2 Chris Hamons 2015-02-24 12:16:59 UTC
I'd like to apologize on the incredibly long delay in replying to this bug. We have a backlog of Xamarin.Mac bugs that we are working through and are working to prevent it from happening it again

So the issue is that you need to be using IntPtr (or some wrapper holding one), when you call objective-c. This works for me

         	[DllImport("/usr/lib/libobjc.dylib")]
		public static extern IntPtr class_getClassMethod(IntPtr aClass, Selector aSelector);
		[DllImport("/usr/lib/libobjc.dylib")]
		public static extern void method_exchangeImplementations(IntPtr a, IntPtr b);

		public override void DidFinishLaunching (NSNotification notification)
		{
			mainWindowController = new MainWindowController ();
			mainWindowController.Window.MakeKeyAndOrderFront (this);
	
			Class bundleClass = new Class("NSBundle");
			IntPtr originalMethod = class_getClassMethod(bundleClass.Handle, new Selector("loadNibNamed:owner:"));
			IntPtr categoryMethod = class_getClassMethod(bundleClass.Handle, new Selector("fake_loadNibNamed:owner:"));
			method_exchangeImplementations(originalMethod, categoryMethod);
		}