xamarin android binding interface method more than 16 parameter how to deal with delegate

[jingliancui]

AndroidApp.zip the java code library sample i create

interfacelongmethodlibrary-debug.zip the java code library aar file i create

Steps to Reproduce

1. Use Vs to create an binding project
2. add this .aar file
3. build
   4.show more than 16 parameter warning and method doesn't generated

I know how to deal the class with this warning,
But it's has an invoker of the interface,I didn't know how to deal with this situation.

Expect:
1.create a class inherited from this interface within the client project(Xamarin.android project).
2.invoke the Client Class' method to trigger the customer interface method.

[jingliancui]

And the key I know is the Fun<> or Action<> just support 15 parameter, so I think you have something solution for this issue which method parameter more than 16 parameter.

[jonpryor]

We need to move away from Func<…>/Action<…> anyway, because our current use only works on Mono, not .NET Framework or .NET Core, and an intention is for Java.Interop to be usable in "normal" desktop environments.

.NET Core intends on introducing a new "more performant" replacement:

• Allow Marshal.GetFunctionPointerForDelegate() to work with generic types runtime#32963
• https://github.com/dotnet/csharplang/blob/master/proposals/function-pointers.md

but I don't see how we can easily use that new infrastructure while continuing to use System.Reflection.Emit within src/Mono.Android/Android.Runtime/JNINativeWrapper.cs, so that's a "long term" idea (probably to also fold into jnimarshalmethod-gen.exe).

Meaning we need to stick with delegates. Non-generic delegates at that.

[jonpryor]

Implementation approach: within generator, instead of hardcoding Action and Func use, we instead need a "2 pass" design.

We define a pattern for defining delegate type names:

• Type name prefix: _JniMarshal_PP
• Parameter types, using JNI encoding, e.g. Z is boolean, I is int, etc. Exception: Reference types, normally encoded as L…;, are instead just L.
• Another _.
• Return type, encoded as with parameters. A void return type is V.

Consider, Java.Lang.Object.Equals():

static Delegate GetEquals_Ljava_lang_Object_Handler ()
{
	if (cb_equals_Ljava_lang_Object_ == null)
		cb_equals_Ljava_lang_Object_ = JNINativeWrapper.CreateDelegate ((Func<IntPtr, IntPtr, IntPtr, bool>) n_Equals_Ljava_lang_Object_);
	return cb_equals_Ljava_lang_Object_;
}

The delegate type on line 4 would instead be _JniMarshal_PPL_Z, resulting in:

static Delegate GetEquals_Ljava_lang_Object_Handler ()
{
	if (cb_equals_Ljava_lang_Object_ == null)
		cb_equals_Ljava_lang_Object_ = JNINativeWrapper.CreateDelegate ((_JniMarshal_PPL_Z) n_Equals_Ljava_lang_Object_);
	return cb_equals_Ljava_lang_Object_;
}

That's the "first" pass.

The second pass is that we need to collect all the types that we're now mentioning in ^^, and then emit them as global internal types:

delegate bool _JniMarshal_PPL_Z (IntPtr jnienv, IntPtr klass, IntPtr a);

This second pass is the "interesting" bit, in that it raises the question: where should these be declared? They could probably be defined in __NamespaceMapping__.cs.

[jingliancui]

@jonpryor

delegate bool _JniMarshal_PPL_Z (IntPtr jnienv, IntPtr klass, IntPtr a);

but the a which is Intptr parameter now map to 16 int args in the aar library.

Now, in debug , I can get the first Intptr value is 0x1 which is I parse value 1 in java code.

But,How to get others paramenter values?
And another question is possible get all value while the 16 parameter have different type ,for example:
int i1,java.lang.string i2,com.others.other.Obj i3 ........ etc.

[jingliancui]

That the binding project I create
InterfaceLongMethodBinding.zip

[jingliancui]

take breakpoint at
App1.Droid.MainActivity line 25,26,27
InterfaceLongMethodBinding/Additions/IInterfaceOne line 96

[jonpryor]

@jingliancui: Please see: https://gist.github.com/jonpryor/8c59d76e44f32ded1bae25c231c0b0e1

[jingliancui]

@jonpryor Fixed it by your workaround, thanks.

[jingliancui]

Is it necessary need this attribute?
[UnmanagedFunctionPointer(CallingConvention.Winapi)]
I try remove this and app run fine , What does this do?