This is a demonstration project showing how twinBASIC can host a .NET 7. Though .NET does support COM activation where the hosting is automatically handled by the internal implementation of the generated .comhost.dll file, this simply show how the hosting can be done manually and controlled by twinBASIC without any COM registration required. Furthermore, the project loads a WPF Page UI control into the window provided by the twinBASIC, demonstrating how to host WPF directly by twinBASIC.

This requires Visual Studio 2022, .NET 7 SDK, and twinBASIC (beta 235). The output should be placed in a folder named Build at the root of directory which is not included in the git repository. The Visual Studio project will attempt to copy the output of its build into the folder which is the same as the output used by twinBASIC's project. The post build event sues a simple copy command that assuems the path exists.

Furthermore, the nethost.dll should be copied from the Resources\nethost.dll into the Build. After a successful build of both projects, the Build folder should contain the minimum of the following files:

• nethost.dll
• WpfClient_win64.exe
• WpfServer.deps.json
• WpfServer.dll
• WpfServer.runtimeconfig.json

The output is tested for 64-bit only and most likely will not work with 32-bit. Because the .NET resources are used in-process by an unmanaged host, the Any CPU is not strictly proper. Therefore, the x64 is the default built in both Visual Studio and twinBASIC project.

In order for the .NET Core library to be dynamically loaded at runtime, it must have the following property in the .csproj:

<EnableDynamicLoading>true</EnableDynamicLoading>

The demonstation does not use the usual approach to activate COM objects via .NET host. Rather, the project uses a function as an entry point to provide the COM object. This can be found in the WpfHostFactory class:

public class WpfHostFactory : IWpfHostFactory
{
	[return: MarshalAs(UnmanagedType.IUnknown)]
	public delegate object CreateWpfHostFactoryDelegate();
	public static object CreateWpfHostFactory()
	{
		return new WpfHostFactory();
	}
	
	...
}

On the twinBASIC side, the function is loaded and called in the MyForm.twin:

If This.CreateFactoryDelegate = 0 Then
	Set This.Manager = New UniversalCaller(This.HostFrxLibraryHandle, STRINGPARAMS_ENUM.STR_NONE, CALLINGCONVENTION_ENUM.CC_CDECL)
	Result = This.Manager.CallDllFunction( _
		AssemblyDelegate, _
		CALLRETURNTUYPE_ENUM.CR_LONGLONG, _
		StrPtr(AssemblyPath), _ 
		StrPtr(TypeName), _ 
		StrPtr(MethodName), _
		StrPtr(DelegateName), _ 
		CLngPtr(0), _ 
		This.CreateFactoryDelegate)
	...
End If

...

Dim Factory As IWpfHostFactory
Set Factory = This.Manager.CallDllFunction( _
	This.CreateFactoryDelegate, _
	CALLRETURNTUYPE_ENUM.CR_OBJECT)

Note furthermore that twinBASIC and .NET project has their own definitions of the interfacess. Compare .NET host's IWpfHost with twinBASIC's IWpfHost for an example. This allows both projects to pass around COM objects without having to register or use regfree approach which would require a separate reference. In a production system, it's probably better to have a separate type library that both projects can reference to avoid having to define the same thing twice in respective language. Nonetheless, this demonstates how a COM object can be passed around without having a type library available.

The demonstration now includes examples of raising events from either side.

From .NET Core, we can raise the MouseDown event from WpfHost by defining a source interface IWpfHostEvents:

[
	ComVisible(true),
	Guid("7F18FA39-1108-4E7F-A8C1-90BB30E96E71"),
	InterfaceType(ComInterfaceType.InterfaceIsIDispatch)
]
public interface IWpfHostEvents
{
	[DispId(1)]
	void MouseDown();
}

and then attach it to the WpfHost:

[
	...
	ComSourceInterfaces(typeof(IWpfHostEvents))
]
public class WpfHost : HwndSource, IWpfHost
{
	...

	internal WpfHost(HwndSourceParameters parameters) : base(parameters)
	{
		...
		_simple.MouseDown += Host_MouseDown;
	}

	private delegate void MouseDownDelegate();
	private event MouseDownDelegate? MouseDown;
	private void Host_MouseDown(object sender, MouseButtonEventArgs e)
	{
		MouseDown?.Invoke();
	}

	...
}

With the corresponding handler in twinBASIC's MyForm.twin:

Private WithEvents Host As WpfHost

...

Private Sub Host_MouseDown() Handles Host.MouseDown
	MsgBox "Mouse down"
End Sub

Using the WpfHost as a coclass:

...

[ InterfaceId ("7F18FA39-1108-4E7F-A8C1-90BB30E96E71") ]
Interface IWpfHostEvents
    [ DispId (1) ]
    Sub MouseDown()
End Interface

[ CoClassId ("19B1E709-EBFD-4561-859D-CD38A8D575AF") ]
CoClass WpfHost
    [ Default ] Interface IWpfHost
    [ Default, Source ] Interface IWpfHostEvents
End CoClass

twinBASIC does not yet support defining a source interface and assigning it to an implementation. However, we still can approximate this by defining an EventInterface and defning the Events the usual way:

[ EventInterfaceId ("C1B1A5B2-979E-409C-B573-7943971A4CCA") ]
Public Class MyForm

...

    Public Event Resize(ByVal Width As Long, ByVal Height As Long)
    Private Sub Form_Resize() Handles Form.Resize
        RaiseEvent Resize(Me.PixelsWidth, Me.PixelsHeight)
    End Sub
    
    Public Event Unload(ByRef Cancel As Boolean)
    Private Sub Form_Unload(Cancel As Integer) Handles Form.Unload
        Dim _Cancel As Boolean = Cancel
        RaiseEvent Unload(_Cancel)
        Cancel = _Cancel
    End Sub
End Class

Then on .NET side, we use ComEventsHelper to listen and respond to the events from twinBASIC. However, we need to pass back the twinBASIC object. We do this via the IWpfHost::Advise:

[ InterfaceId ("19B1E709-EBFD-4561-859D-CD38A8D575AF") ]
Interface IWpfHost
    Sub Advise(Client As Object)
    ...
End Interface

The IWpfHost interface is also defined in the .NET project. We respond to the Advise method and call ComEventsHelper.Combine():

public class WpfHost : HwndSource, IWpfHost
{
    ...
	
	private void Host_Resize(int width, int height)
	{
		MessageBox.Show($"New size: {width}, {height}");
	}

	private void Host_Unload(ref bool cancel)
	{
		cancel = MessageBox.Show("Close?", default, MessageBoxButton.YesNo) != MessageBoxResult.Yes;
	}

	public void Advise([MarshalAs(UnmanagedType.IUnknown)] ref object client)
	{
		ComEventsHelper.Combine(client, new Guid("C1B1A5B2-979E-409C-B573-7943971A4CCA"), 1, Host_Resize);
		ComEventsHelper.Combine(client, new Guid("C1B1A5B2-979E-409C-B573-7943971A4CCA"), 2, Host_Unload);
	}
}

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