Integrating a C# Library in Flutter App

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1

I have a legacy C# code that has some math logic in it. Re-writing all of that in Dart will be time taking. Is there a way to use the C# library into Flutter app ?

2

Directly this probably will be difficult but maybe someone has an idea. Maybe by using managed c++ in .Net as a proxy that you could reach via FFI?

I would try to see if there is a way via FFI to access a c# library.

Alternatively I m pretty sure that AI would be able to convert c# code to Dart

3

Thanks for your quick response. I think FFI is mainly for C libraries and not for C#

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4

I wrote a Medium article on this very topic some time ago, may help you.

https://medium.com/@stevehamblett/using-c-libraries-in-dart-ec630848d52c?source=friends_link&sk=5e10a91a1a8169c3f29669f697664672

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5

You can do this: Is is possible to export functions from a C# DLL like in VS C++? - Stack Overflow

And then use it from dart as if you were using a C library

6

Honestly, I’d really love to see Dart’s larger FFI strategy also seek to extend to Web Assembly’s emerging component model. That would open up a huge amount of safe and standardised cross language interoperability where the value would grow over time without necessarily needing much in the way of ongoing investment from the team.

Specifically, I was thinking of maybe using the existing C interoperability to wrap something like the Wasmtime runtime (a single C header file) as many other languages have done but that would be a good example of how C# could be supported without needing to do a lot of C# specific work since they already have web assembly modules as a compilation target in that ecosystem.

Note: this isn’t the same as also having Dart be able to compile to Wasm runtimes outside of the browser although I would love to see that as well very much but this seemed like a much smaller and reasonable bit of work to simple be able to embed a WASI runtime to consume those modules.

7

@shamblett , Thanks a lot for your response. I am trying to execute your example in Windows. I am publishing the library using the command

dotnet publish /p:NativeLib=Shared /p:SelfContained=true -r win-x64 -c debug

and edited Line 9 of Dart file as follows

final lib = DynamicLibrary.open('../bin/debug/net9.0/win-x64/publish/NativeLibrary.dll');

NativeLibrary.dll exists in the proper location , However, I am getting an error when the add function is called in line 12

Erroring code:

Pointer<NativeFunction<Cfunc>> cadd = lib.lookup<NativeFunction<Cfunc>>('add')

Error message

Opening.....
Associating.....
Unhandled exception:
Invalid argument(s): Failed to lookup symbol 'add': The specified procedure could not be found.
 (error code: 127)
#0      DynamicLibrary.lookup (dart:ffi-patch/ffi_dynamic_library_patch.dart:33:70)
#1      main (file:///C:/example/NativeLibrary/dart/add.dart:12:45)
#2      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:297:19)
#3      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

What am I doing wrong ?

8

Not sure, I haven’t tried this on windows myself, however there is an issue raised on the repo by another Windows user about a similar situation. This may help you.