How to declare method in c# with parameters as handler and map that to obj-C native binding library in Xamarin iOS?

Question

Obj-C syntax for the method:

Starts MyIP service.

@param onMyIpSuccess It is called when MyIP service detects IP change. @see MyIpServiceSuccessHandler. @param onMyIpFailure It is called when MyIP service gets an error. @see MyIpServiceFailureHandler. */

(void)startMyIpServiceWithSuccess:(MyIpServiceSuccessHandler _Nonnull)onMyIpSuccess failure:(MyIpServiceFailureHandler _Nonnull)onMyIpFailure;

/**

C# Class:

I created 2 delegates as

public delegate void MyIpServiceSuccessHandler(string ip);
public delegate void MyIpServiceFailureHandler(GCMyIpError error);

and write method as

[Export("startMyIpServiceWithSuccess:failure:")]
public virtual void StartMyIpService(MyIpServiceSuccessHandler onMyIpSuccess, MyIpServiceFailureHandler onMyIpFailure)
{            
  if (IsDirectBinding)
  {
    Messaging.void_objc_msgSend_IntPtr_IntPtr(this.Handle, 
                   Selector.GetHandle("startMyIpServiceWithSuccess:failure:"), 
                   Marshal.GetFunctionPointerForDelegate(onMyIpSuccess), 
                   Marshal.GetFunctionPointerForDelegate(onMyIpFailure));   
   }
}

When i am calling StartMyIpService from another class having methods defined as:

[MonoPInvokeCallback(typeof(GCClient.MyIpServiceSuccessHandler))]
static void MyIpServiceSuccess(string ip)
{
   // To do
}

[MonoPInvokeCallback(typeof(GCClient.MyIpServiceFailureHandler))]
static unsafe void MyIpServiceFailure(GCMyIpError error)
{
   // To do
}

and calling native binding methods StartMyIpService as:

_gcClient.StartMyIpService(MyIpServiceSuccess, MyIpServiceFailure);

Run time error when StartMyIPService method triggers

=================================================================
    Native Crash Reporting
=================================================================
Got a segv while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.
=================================================================

=================================================================
    Native stacktrace:
=================================================================
    0x105ada884 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105ad09fc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105aded04 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x1f1be6c10 - /usr/lib/system/libsystem_platform.dylib : <redacted>
    0x10632f098 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/Frameworks/GeoComplySDK.framework/GeoComplySDK : -[GeoComplyClient startMyIpServiceWithSuccess:failure:]
    0x105a68204 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105a60e60 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105a6359c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105a72084 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa2e0c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105a6c040 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105a70ee4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa548c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a7bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a5bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa5348 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f495a4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f496d4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f488ec - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f42d40 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f41110 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f3bdb4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa3b4c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105a71d24 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa548c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a7bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a5bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa5348 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f495a4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f496d4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f488ec - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f42d40 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f41110 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f3bdb4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa3b4c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x1054e9590 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa548c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a7bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a5bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa5348 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f495a4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f496d4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f488ec - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f42d40 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f41110 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f3bdb4 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa3b4c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x1054e2390 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa548c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a7bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f2a5bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102fa5348 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102f48d48 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x10326a5bc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x1031b4c70 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105ae214c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x105b9bd28 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x105b9f568 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x102e002b0 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102e00798 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x1831133c8 - /System/Library/Frameworks/Foundation.framework/Foundation : <redacted>
    0x18196f020 - /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation : <redacted>
    0x18197fce0 - /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation : <redacted>
    0x1818b9fe8 - /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation : <redacted>
    0x1818bf7f4 - /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation : <redacted>
    0x1818d33b8 - /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation : CFRunLoopRunSpecific
    0x19d26338c - /System/Library/PrivateFrameworks/GraphicsServices.framework/GraphicsServices : GSEventRunModal
    0x1842736a8 - /System/Library/PrivateFrameworks/UIKitCore.framework/UIKitCore : <redacted>
    0x183ff27f4 - /System/Library/PrivateFrameworks/UIKitCore.framework/UIKitCore : UIApplicationMain
    0x103321018 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x103294590 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x102e2f4c8 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x1031b4c70 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105ae214c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x105b9bd28 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x105ba1fdc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : mono_pmip
    0x105ac055c - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x105ca4ad0 - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : xamarin_log
    0x102e2f3dc - /private/var/containers/Bundle/Application/7DAF9748-8382-43D7-9AB7-F0C8EB69330D/MGM.iOS.app/MGM.iOS : 
    0x1063d5a24 - Unknown

=================================================================
    Basic Fault Address Reporting
=================================================================
Memory around native instruction pointer (0x199faf490):0x199faf480  1f 04 00 f1 eb 03 00 54 08 00 40 f9 09 81 7d 92  .......T..@...}.
0x199faf490  2a 11 40 f9 2a 02 10 36 08 03 00 36 09 20 e0 d2  *.@.*..6...6. ..
0x199faf4a0  0a fd 77 d3 ea 02 00 b4 0b 01 09 ab 22 01 00 54  ..w........."..T
0x199faf4b0  ea 03 08 aa 0b 7c aa c8 5f 01 08 eb 20 02 00 54  .....|.._... ..T

=================================================================
    Managed Stacktrace:
=================================================================
      at <unknown> <0xffffffff>
      at PLEE.GeoComplyCore.iOS.Messaging:void_objc_msgSend_IntPtr_IntPtr <0x00007>
      at PLEE.GeoComplyCore.iOS.GeoComplyClient:StartMyIpService <0x0020f>
      at PLEE.GeoComplyCore.iOS.GeoComplyServiceIos:RequestLocation <0x0077b>
      at <FetchLocation>d__27:MoveNext <0x00243>
      at System.Runtime.CompilerServices.AsyncVoidMethodBuilder:Start <0x0007b>
      at PLEE.GeoComplyCore.GeoComplyServiceBase:FetchLocation <0x001ff>
      at <PlayerLogin>d__25:MoveNext <0x00d53>
      at MoveNextRunner:InvokeMoveNext <0x0009b>
      at System.Threading.ExecutionContext:RunInternal <0x001ab>
      at System.Threading.ExecutionContext:Run <0x0002b>
      at MoveNextRunner:Run <0x000c7>
      at System.Threading.Tasks.AwaitTaskContinuation:InvokeAction <0x00053>
      at System.Threading.Tasks.AwaitTaskContinuation:RunCallback <0x00063>
      at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation:Run <0x0013b>
      at System.Threading.Tasks.Task:FinishContinuations <0x002ef>
      at System.Threading.Tasks.Task:FinishStageThree <0x0009f>
      at System.Threading.Tasks.Task`1:TrySetResult <0x00133>
      at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1:SetResult <0x000db>
      at <RetrieveGeoComplyLicenseFromOperator>d__26:MoveNext <0x00893>
      at MoveNextRunner:InvokeMoveNext <0x0009b>
      at System.Threading.ExecutionContext:RunInternal <0x001ab>
      at System.Threading.ExecutionContext:Run <0x0002b>
      at MoveNextRunner:Run <0x000c7>
      at System.Threading.Tasks.AwaitTaskContinuation:InvokeAction <0x00053>
      at System.Threading.Tasks.AwaitTaskContinuation:RunCallback <0x00063>
      at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation:Run <0x0013b>
      at System.Threading.Tasks.Task:FinishContinuations <0x002ef>
      at System.Threading.Tasks.Task:FinishStageThree <0x0009f>
      at System.Threading.Tasks.Task`1:TrySetResult <0x00133>
      at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1:SetResult <0x000db>
      at <GCC_GetLicense>d__12:MoveNext <0x0037f>
      at MoveNextRunner:InvokeMoveNext <0x0009b>
      at System.Threading.ExecutionContext:RunInternal <0x001ab>
      at System.Threading.ExecutionContext:Run <0x0002b>
      at MoveNextRunner:Run <0x000c7>
      at System.Threading.Tasks.AwaitTaskContinuation:InvokeAction <0x00053>
      at System.Threading.Tasks.AwaitTaskContinuation:RunCallback <0x00063>
      at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation:Run <0x0013b>
      at System.Threading.Tasks.Task:FinishContinuations <0x002ef>
      at System.Threading.Tasks.Task:FinishStageThree <0x0009f>
      at System.Threading.Tasks.Task`1:TrySetResult <0x00133>
      at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1:SetResult <0x000db>
      at <PostFunc>d__8`2:MoveNext <0x0087f>
      at MoveNextRunner:InvokeMoveNext <0x0009b>
      at System.Threading.ExecutionContext:RunInternal <0x001ab>
      at System.Threading.ExecutionContext:Run <0x0002b>
      at MoveNextRunner:Run <0x000c7>
      at <>c:<.cctor>b__7_0 <0x00057>
      at Foundation.NSAsyncSynchronizationContextDispatcher:Apply <0x0002b>
      at System.Object:runtime_invoke_dynamic <0x0010f>
      at <unknown> <0xffffffff>
      at UIKit.UIApplication:UIApplicationMain <0x00007>
      at UIKit.UIApplication:Main <0x000ef>
      at MGM.iOS.Application:Main <0x00077>
      at System.Object:runtime_invoke_dynamic <0x0010f>
=================================================================

At first, you can try to use the try catch to check the detail error message. And then you can add a break point to check which line causes the crash. In addition, have you read the [official document](https://learn.microsoft.com/en-us/xamarin/ios/platform/binding-objective-c/) about the binding object c? — Liyun Zhang - MSFT, Jul 31 '22 at 03:15
@LiyunZhang-MSFT The line below causes the crash Messaging.void_objc_msgSend_IntPtr_IntPtr(this.Handle, Selector.GetHandle("startMyIpServiceWithSuccess:failure:"), Marshal.GetFunctionPointerForDelegate(onMyIpSuccess), Marshal.GetFunctionPointerForDelegate(onMyIpFailure)); — user3162111, Jul 31 '22 at 14:32

How to declare method in c# with parameters as handler and map that to obj-C native binding library in Xamarin iOS?

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