How to Invoke the IntPtr result of method_getImplementation

Question

The result of calling method_getImplementation(method) is an IntPtr. How do I convert an IntPtr to a method?

[DllImport("/usr/lib/libobjc.dylib")]
extern static IntPtr method_getImplementation(IntPtr method);

public void SomeMethod
{
var method = class_getInstanceMethod(new UIViewController().ClassHandle, new Selector("viewWillAppear:").Handle);

IntPtr original_impl = method_getImplementation(method);
}

In obj-c:

IMP originalImp = method_setImplementation(method,swizzleImp);
originalImp(self,_cmd)

Gotta be honest, this looks like the sort of plumbing the interop layer should be handling, since in general you just flat-out can't call arbitrary memory locations from managed code. So maybe a bit of an XY problem? What are you trying to do that involves this? — Nathan Tuggy, Feb 17 '15 at 06:31
This, http://stackoverflow.com/questions/14127453/how-to-port-method-getimplementation-and-method-setimplementation-to-monotou — Derek Beattie, Feb 17 '15 at 07:12
Hmm, maybe this: http://stackoverflow.com/questions/12767903/create-delegate-at-runtime-from-native-method-on-ios — Derek Beattie, Feb 17 '15 at 16:42

score 1 · Accepted Answer · answered Feb 18 '15 at 08:37

You need to use Marshal.GetDelegateForFunctionPointer and add [MonoNativeFunctionWrapper] to the delegate type:

[MonoNativeFunctionWrapper]
public delegate void ViewWillAppearDelegate (IntPtr self, IntPtr selector);

var del = (ViewWillAppearDelegate) Marshal.GetDelegateForFunctionPointer (original_impl, typeof (ViewWillAppearDelegate));
del (obj.Handle, Selector.GetHandle ("viewWillAppear"));

How to Invoke the IntPtr result of method_getImplementation

1 Answers1