Unable to use ICustomTypeDescriptor in C++/CLI

[hmisaki]

Description

I am working on the dotnet 9 migration in our repo.
When I tried to build a managed C++ project, it failed. The error log shows :

1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18): error C3766: 'test' must provide an implementation for the interface method 'System::Nullable<bool> System::ComponentModel::ICustomTypeDescriptor::RequireRegisteredTypes::get(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18): error C3766: 'test' must provide an implementation for the interface method 'System::ComponentModel::TypeConverter ^System::ComponentModel::ICustomTypeDescriptor::GetConverterFromRegisteredType(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18): error C3766: 'test' must provide an implementation for the interface method 'System::ComponentModel::EventDescriptorCollection ^System::ComponentModel::ICustomTypeDescriptor::GetEventsFromRegisteredType(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18): error C3766: 'test' must provide an implementation for the interface method 'System::ComponentModel::PropertyDescriptorCollection ^System::ComponentModel::ICustomTypeDescriptor::GetPropertiesFromRegisteredType(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18): warning C4570: 'test': is not explicitly declared as abstract but has abstract functions
1>.NETCoreApp,Version=v9.0.AssemblyAttributes.cpp
1>    E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18):
1>    'System::Nullable<bool> System::ComponentModel::ICustomTypeDescriptor::RequireRegisteredTypes::get(void)': is abstract
1>    E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18):
1>    'System::ComponentModel::TypeConverter ^System::ComponentModel::ICustomTypeDescriptor::GetConverterFromRegisteredType(void)': is abstract
1>    E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18):
1>    'System::ComponentModel::EventDescriptorCollection ^System::ComponentModel::ICustomTypeDescriptor::GetEventsFromRegisteredType(void)': is abstract
1>    E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(4,18):
1>    'System::ComponentModel::PropertyDescriptorCollection ^System::ComponentModel::ICustomTypeDescriptor::GetPropertiesFromRegisteredType(void)': is abstract
1>Generating Code...
1>Done building project "managed2.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

It seems it's related to C++/CLI doesn't support the default interface method.

Reproduction Steps

Create a managed C++ project in Visual Studio and fill it with the following codes:

using namespace System::ComponentModel;
using namespace System;
public ref class test : ICustomTypeDescriptor
{
public:
    virtual Object^ GetPropertyOwner(PropertyDescriptor^ pd) { return nullptr; }
    virtual AttributeCollection^ GetAttributes(void) { return nullptr; }
    virtual String^ GetClassName(void) { return nullptr; }
    virtual String^ GetComponentName(void) { return nullptr; }
    virtual TypeConverter^ GetConverter(void) { return nullptr; }
    virtual EventDescriptor^ GetDefaultEvent(void) { return nullptr; }
    virtual PropertyDescriptor^ GetDefaultProperty(void) { return nullptr; }
    virtual Object^ GetEditor(Type^ editorBaseType) { return nullptr; }
    virtual EventDescriptorCollection^ GetEvents(cli::array<Attribute^>^ attributes) { return nullptr; }
    virtual EventDescriptorCollection^ GetEvents(void) { return nullptr; }
    virtual System::ComponentModel::PropertyDescriptorCollection^ GetProperties(void) { return nullptr; }
    virtual System::ComponentModel::PropertyDescriptorCollection^ GetProperties(cli::array<Attribute^>^ attributes) { return nullptr; }
};

Then, compile the project.

Expected behavior

Build success.

Actual behavior

Build fail.

Regression?

Yes, I can build these code on .net 8

Known Workarounds

No

Configuration

No response

Other information

No response

[huoyaoyuan]

C++/CLI compiler doesn't handle default interface method in this case.

[hmisaki]

Is there any solution or workaround to fix in my scenario? We have too much usage like this.

[huoyaoyuan]

What version of MSVC compiler are you using? There are several updates for type system recently.

[JavaScript-Py]

Hello!

In .NET 9, ICustomTypeDescriptor includes new members with default implementations, such as:

RequireRegisteredTypes
GetConverterFromRegisteredType
GetEventsFromRegisteredType
GetPropertiesFromRegisteredType
These default interface methods are abstract in managed C++/CLI because it does not yet fully support DIMs, requiring explicit implementation.

Managed C++ does not seamlessly support default interface methods added in newer .NET versions, necessitating the explicit implementation of all interface members, even those with default implementations in .NET languages like C#.

  #include "pch.h"
  
  using namespace System;
  using namespace System::ComponentModel;
  
  public ref class MyCustomTypeDescriptor : public ICustomTypeDescriptor
  {
  
  public:
      virtual Object^ GetPropertyOwner(PropertyDescriptor^ pd) override { return nullptr; }
      virtual AttributeCollection^ GetAttributes(void) override { return AttributeCollection::Empty; }
      virtual String^ GetClassName(void) override { return "MyCustomTypeDescriptor"; }
      virtual String^ GetComponentName(void) override { return nullptr; }
      virtual TypeConverter^ GetConverter(void) override { return gcnew TypeConverter(); }
      virtual EventDescriptor^ GetDefaultEvent(void) override { return nullptr; }
      virtual PropertyDescriptor^ GetDefaultProperty(void) override { return nullptr; }
      virtual Object^ GetEditor(Type^ editorBaseType) override { return nullptr; }
  
      virtual EventDescriptorCollection^ GetEvents(void) override { return EventDescriptorCollection::Empty; }
  
      virtual EventDescriptorCollection^ GetEvents(cli::array<Attribute^>^ attributes) override
      {
          return EventDescriptorCollection::Empty;
      }
  
      virtual PropertyDescriptorCollection^ GetProperties(void) override { return PropertyDescriptorCollection::Empty; }
  
      virtual PropertyDescriptorCollection^ GetProperties(cli::array<Attribute^>^ attributes) override
      {
          return PropertyDescriptorCollection::Empty;
      }
  };

I tried here and worked fine, I hope it helps you.

I used C++/CLI support for v143 build tools (Latest).

To execute: Do not forget the Main() from cpp

[hmisaki]

Hi, @huoyaoyuan The MSVC version is 14.40.33807.

[hmisaki]

Hi @JavaScript-Py , I am glad to get a workaround from you. I copied the code and tried to compile my test project, but there are still the same issues:

1>    Matching base method 'System::ComponentModel::ICustomTypeDescriptor::GetProperties' is from an interface class (not a ref class)
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(27,18): error C3766: 'MyCustomTypeDescriptor' must provide an implementation for the interface method 'System::Nullable<bool> System::ComponentModel::ICustomTypeDescriptor::RequireRegisteredTypes::get(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(27,18): error C3766: 'MyCustomTypeDescriptor' must provide an implementation for the interface method 'System::ComponentModel::TypeConverter ^System::ComponentModel::ICustomTypeDescriptor::GetConverterFromRegisteredType(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(27,18): error C3766: 'MyCustomTypeDescriptor' must provide an implementation for the interface method 'System::ComponentModel::EventDescriptorCollection ^System::ComponentModel::ICustomTypeDescriptor::GetEventsFromRegisteredType(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(27,18): error C3766: 'MyCustomTypeDescriptor' must provide an implementation for the interface method 'System::ComponentModel::PropertyDescriptorCollection ^System::ComponentModel::ICustomTypeDescriptor::GetPropertiesFromRegisteredType(void)'
1>E:\MySpace\TestDefaultMethonInterface\Library1\managed2\test.cpp(27,18): warning C4570: 'MyCustomTypeDescriptor': is not explicitly declared as abstract but has abstract functions

I have tried to fix it by adding implementations in the C++/CLI class :

    virtual TypeConverter^ GetConverterFromRegisteredType()
    {
        return nullptr;
    }
    virtual EventDescriptorCollection^ GetEventsFromRegisteredType()
    {
        return nullptr;
    }
    virtual System::ComponentModel::PropertyDescriptorCollection^ GetPropertiesFromRegisteredType()
    {
        return nullptr;
    }
    property virtual System::Nullable<bool> RequireRegisteredTypes {
        System::Nullable<bool> get() { return false; }
    }

That will make the build pass, but I am worried that it might cause the runtime to fail.

[huoyaoyuan]

Seems that the latest version of msvc hasn't provide support for default interface method, and you have to provide implementation of the methods.

That will make the build pass, but I am worried that it might cause the runtime to fail.

It should run fine. You can copy the default implementation of the methods from C# source at https://github.com/dotnet/runtime/blob/main/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ICustomTypeDescriptor.cs .

[steveharter]

Closing; please report back if the work-around of adding the default implementation works.