VB Net/Com Interoperability/Late Binding


M

Mike

Hi All,

We are in the process of upgrading some VB6 code to .Net Specifically, we are re-writing some class definitions in the .Net environment to still be used in VB6. I think we have most of the stumbling blocks figured out, however, there is one design requirement due to poor programming that we need to implement. This requirement is to be able to have access to all child properties from its parent. Let's do a simple example that may illustrate this.

VB.Net Code

Public Class myBaseClass

Public myBaseClassProp As String

End Class

Public Class myDerivedClass
Inherits myBaseClass

Public myDerivedClassProp As String

End Class

From within VB6 I need to be able to access myBaseClss.myDerivedClassProp through code like

Dim md As New myDerivedClass
Dim mb as myBaseClass

Set mb=md

mb.myDerivedClassProp="test"

I did find the following blurb from the below website to slightly lead me in the right direction. However, it didn't give any examples or indications of actually how to go about doing this. I know if I can somehow override the Interfaces below, we can write our own implementation and use Reflections to get the property that we are looking for. I would also like to be able to do a mixture of early and late binding(which I don't know if it is possible) where all the regular properties are made available through intellisense and so that the application performs best.

The website/blurb is as follows:

http://msdn.microsoft.com/en-us/library/111chfb8(VS.80).aspx

In addition to exposing the interfaces that are explicitly implemented by a class in the managed environment, the .NET Framework supplies implementations of the COM interfaces listed in the following table on behalf of the object. A .NET class can override the default behavior by providing its own implementation of these interfaces. However, the runtime always provides the implementation for the IUnknown and IDispatch interfaces.

Interface Description
Idispatch
Provides a mechanism for late binding to type.

IerrorInfo
Provides a textual description of the error, its source, a Help file, Help context, and the GUID of the interface that defined the error (always GUID_NULL for .NET classes).

IprovideClassInfo
Enables COM clients to gain access to the ITypeInfo interface implemented by a managed class.

IsupportErrorInfo
Enables a COM client to determine whether the managed object supports the IErrorInfo interface. If so, enables the client to obtain a pointer to the latest exception object. All managed types support the IErrorInfo interface.

ItypeInfo
Provides type information for a class that is exactly the same as the type information produced by Tlbexp.exe.

Iunknown
Provides the standard implementation of the IUnknown interface with which the COM client manages the lifetime of the CCW and provides type coercion.
 
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F

Family Tree Mike

Hi All,

We are in the process of upgrading some VB6 code to .Net Specifically, we are re-writing some class definitions in the .Net environment to still be used in VB6. I think we have most of the stumbling blocks figured out, however, there is one design requirement due to poor programming that we need to implement. This requirement is to be able to have access to all child properties from its parent. Let's do a simple example that may illustrate this.

VB.Net Code

Public Class myBaseClass

Public myBaseClassProp As String

End Class

Public Class myDerivedClass
Inherits myBaseClass

Public myDerivedClassProp As String

End Class

From within VB6 I need to be able to access myBaseClss.myDerivedClassProp through code like

Dim md As New myDerivedClass
Dim mb as myBaseClass

Set mb=md

mb.myDerivedClassProp="test"

I did find the following blurb from the below website to slightly lead me in the right direction. However, it didn't give any examples or indications of actually how to go about doing this. I know if I can somehow override the Interfaces below, we can write our own implementation and use Reflections to get the property that we are looking for. I would also like to be able to do a mixture of early and late binding(which I don't know if it is possible) where all the regular properties are made available through intellisense and so that the application performs best.

The website/blurb is as follows:

http://msdn.microsoft.com/en-us/library/111chfb8(VS.80).aspx

In addition to exposing the interfaces that are explicitly implemented by a class in the managed environment, the .NET Framework supplies implementations of the COM interfaces listed in the following table on behalf of the object. A .NET class can override the default behavior by providing its own implementation of these interfaces. However, the runtime always provides the implementation for the IUnknown and IDispatch interfaces.

Interface Description
Idispatch
Provides a mechanism for late binding to type.

IerrorInfo
Provides a textual description of the error, its source, a Help file, Help context, and the GUID of the interface that defined the error (always GUID_NULL for .NET classes).

IprovideClassInfo
Enables COM clients to gain access to the ITypeInfo interface implemented by a managed class.

IsupportErrorInfo
Enables a COM client to determine whether the managed object supports the IErrorInfo interface. If so, enables the client to obtain a pointer to the latest exception object. All managed types support the IErrorInfo interface.

ItypeInfo
Provides type information for a class that is exactly the same as the type information produced by Tlbexp.exe.

Iunknown
Provides the standard implementation of the IUnknown interface with which the COM client manages the lifetime of the CCW and provides type coercion.





--
Thanks,

Mike


In general, this would not make sense, because of the following example:

public class vehical
end class

public class car
inherits vehical
public string MufflerType
end class

public class airplane
inherits vehical
public string WingType
end class

Given your scenario, you would be trying (potentially) to get the wingtype of a car, or the mufflertype of an airplane.

It's been years since I looked at VB 6 code, but I cannot think you could to that in VB 6 either.
 
M

Mike

Thanks for the reply Mike..

Sadly, I know it is somehow possible. The third party program that we are replacing allowed for it. I do not know what language the program was written in(quite possibly c or c++). However, to minimize the amount of code changes it would be nice to be able to duplicate this functionality. I'm fairly certain that the third party program we were utilizing did this somehow through late binding as none of the properties like that show up through VB6's intelli sense.

The backup plan that I have proposed to the group is to create a Properties method on each class that utilizes reflection to find that function and then either sets or gets the correct value.

--
Thanks,

Mike Wiles
Hi All,

We are in the process of upgrading some VB6 code to .Net Specifically, we are re-writing some class definitions in the .Net environment to still be used in VB6. I think we have most of the stumbling blocks figured out, however, there is one design requirement due to poor programming that we need to implement. This requirement is to be able to have access to all child properties from its parent. Let's do a simple example that may illustrate this.

VB.Net Code

Public Class myBaseClass

Public myBaseClassProp As String

End Class

Public Class myDerivedClass
Inherits myBaseClass

Public myDerivedClassProp As String

End Class

From within VB6 I need to be able to access myBaseClss.myDerivedClassProp through code like

Dim md As New myDerivedClass
Dim mb as myBaseClass

Set mb=md

mb.myDerivedClassProp="test"

I did find the following blurb from the below website to slightly lead me in the right direction. However, it didn't give any examples or indications of actually how to go about doing this. I know if I can somehow override the Interfaces below, we can write our own implementation and use Reflections to get the property that we are looking for. I would also like to be able to do a mixture of early and late binding(which I don't know if it is possible) where all the regular properties are made available through intellisense and so that the application performs best.

The website/blurb is as follows:

http://msdn.microsoft.com/en-us/library/111chfb8(VS.80).aspx

In addition to exposing the interfaces that are explicitly implemented by a class in the managed environment, the .NET Framework supplies implementations of the COM interfaces listed in the following table on behalf of the object. A .NET class can override the default behavior by providing its own implementation of these interfaces. However, the runtime always provides the implementation for the IUnknown and IDispatch interfaces.

Interface Description
Idispatch
Provides a mechanism for late binding to type.

IerrorInfo
Provides a textual description of the error, its source, a Help file, Help context, and the GUID of the interface that defined the error (always GUID_NULL for .NET classes).

IprovideClassInfo
Enables COM clients to gain access to the ITypeInfo interface implemented by a managed class.

IsupportErrorInfo
Enables a COM client to determine whether the managed object supports the IErrorInfo interface. If so, enables the client to obtain a pointer to the latest exception object. All managed types support the IErrorInfo interface.

ItypeInfo
Provides type information for a class that is exactly the same as the type information produced by Tlbexp.exe.

Iunknown
Provides the standard implementation of the IUnknown interface with which the COM client manages the lifetime of the CCW and provides type coercion.





--
Thanks,

Mike


In general, this would not make sense, because of the following example:

public class vehical
end class

public class car
inherits vehical
public string MufflerType
end class

public class airplane
inherits vehical
public string WingType
end class

Given your scenario, you would be trying (potentially) to get the wingtype of a car, or the mufflertype of an airplane.

It's been years since I looked at VB 6 code, but I cannot think you could to that in VB 6 either.
 
P

Patrice

Hello,

The proper way to do that from a mb variable would be precisely to do something such as :
Set md=mb ' Will fails if mb doesn't hold a reference to MyDerivedClass
md.myDerivedClassProp="Test"

That is exactly what you are trying to escape from...

IMO the easiest way to do this using VB6 would be likely to use late binding at least for this particular object/call :

Dim md As New myDerivedClass
Dim mb as Object
Set mb=md
mb.myDerivedClassProp="test"


I understand you are trying to minimize code changes (but you the existing source code is in some other language than VB 6 ??? and I don't see how it could have worked in VB6 until now) but I would still double check if it's not better to design correctly now rather than to reproduce an awkward design that will keep bothering you forever...

--
Patrice

"Mike" <[email protected]> a écrit dans le message de groupe de discussion : %237KdKKn9J[email protected]
Hi All,

We are in the process of upgrading some VB6 code to .Net Specifically, we are re-writing some class definitions in the .Net environment to still be used in VB6. I think we have most of the stumbling blocks figured out, however, there is one design requirement due to poor programming that we need to implement. This requirement is to be able to have access to all child properties from its parent. Let's do a simple example that may illustrate this.

VB.Net Code

Public Class myBaseClass

Public myBaseClassProp As String

End Class

Public Class myDerivedClass
Inherits myBaseClass

Public myDerivedClassProp As String

End Class

From within VB6 I need to be able to access myBaseClss.myDerivedClassProp through code like

Dim md As New myDerivedClass
Dim mb as myBaseClass

Set mb=md

mb.myDerivedClassProp="test"

I did find the following blurb from the below website to slightly lead me in the right direction. However, it didn't give any examples or indications of actually how to go about doing this. I know if I can somehow override the Interfaces below, we can write our own implementation and use Reflections to get the property that we are looking for. I would also like to be able to do a mixture of early and late binding(which I don't know if it is possible) where all the regular properties are made available through intellisense and so that the application performs best.

The website/blurb is as follows:

http://msdn.microsoft.com/en-us/library/111chfb8(VS.80).aspx

In addition to exposing the interfaces that are explicitly implemented by a class in the managed environment, the .NET Framework supplies implementations of the COM interfaces listed in the following table on behalf of the object. A .NET class can override the default behavior by providing its own implementation of these interfaces. However, the runtime always provides the implementation for the IUnknown and IDispatch interfaces.

Interface Description
Idispatch
Provides a mechanism for late binding to type.

IerrorInfo
Provides a textual description of the error, its source, a Help file, Help context, and the GUID of the interface that defined the error (always GUID_NULL for .NET classes).

IprovideClassInfo
Enables COM clients to gain access to the ITypeInfo interface implemented by a managed class.

IsupportErrorInfo
Enables a COM client to determine whether the managed object supports the IErrorInfo interface. If so, enables the client to obtain a pointer to the latest exception object. All managed types support the IErrorInfo interface.

ItypeInfo
Provides type information for a class that is exactly the same as the type information produced by Tlbexp.exe.

Iunknown
Provides the standard implementation of the IUnknown interface with which the COM client manages the lifetime of the CCW and provides type coercion.
 
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M

Mike

Thanks for the info. I'll have to see if that will work. Do you know what .Net COM attributes I need to set above my class in order to make that work? Does that approach mix early and late binding? Late binding is an expensive operation, so it would be nice to early bind the known properties and then late bind the unknown properties. This should allow our intellisense to work for the early bound properties as well.

Reworking the code is definitely a possibility that we are considering. I do have a solution using Reflections that I can simulate the same thing using a function call. We just have a very short window of time to write the code. I basically wrote two .Net properties as a work around, an obj.Properties("myDerivedProp") and and obj.setProperty("myDerivedProp", value). The obj.Properties("myDerivedProp") works for returning values and setting non number or string values, but works for class objects. This is due to the way things get exported to COM from .Net. obj.setProperty("myDerivedProp", value) works with all types of data.

Our application is in VB6. However, our object manager is written in by a 3rd party that we don't have access to. If I had to take a guess, I'm guessing that it was written in C++ because what I've read shows that in C++ you write your own IUnknown and IDispatch events, which I think is how I think they got away with it.

--
Thanks,

Mike Wiles
"Patrice" <http://scribe-en.blogspot.com/> wrote in message Hello,

The proper way to do that from a mb variable would be precisely to do something such as :
Set md=mb ' Will fails if mb doesn't hold a reference to MyDerivedClass
md.myDerivedClassProp="Test"

That is exactly what you are trying to escape from...

IMO the easiest way to do this using VB6 would be likely to use late binding at least for this particular object/call :

Dim md As New myDerivedClass
Dim mb as Object
Set mb=md
mb.myDerivedClassProp="test"


I understand you are trying to minimize code changes (but you the existing source code is in some other language than VB 6 ??? and I don't see how it could have worked in VB6 until now) but I would still double check if it's not better to design correctly now rather than to reproduce an awkward design that will keep bothering you forever...

--
Patrice

"Mike" <[email protected]> a écrit dans le message de groupe de discussion : %[email protected]
Hi All,

We are in the process of upgrading some VB6 code to .Net Specifically, we are re-writing some class definitions in the .Net environment to still be used in VB6. I think we have most of the stumbling blocks figured out, however, there is one design requirement due to poor programming that we need to implement. This requirement is to be able to have access to all child properties from its parent. Let's do a simple example that may illustrate this.

VB.Net Code

Public Class myBaseClass

Public myBaseClassProp As String

End Class

Public Class myDerivedClass
Inherits myBaseClass

Public myDerivedClassProp As String

End Class

From within VB6 I need to be able to access myBaseClss.myDerivedClassProp through code like

Dim md As New myDerivedClass
Dim mb as myBaseClass

Set mb=md

mb.myDerivedClassProp="test"

I did find the following blurb from the below website to slightly lead me in the right direction. However, it didn't give any examples or indications of actually how to go about doing this. I know if I can somehow override the Interfaces below, we can write our own implementation and use Reflections to get the property that we are looking for. I would also like to be able to do a mixture of early and late binding(which I don't know if it is possible) where all the regular properties are made available through intellisense and so that the application performs best.

The website/blurb is as follows:

http://msdn.microsoft.com/en-us/library/111chfb8(VS.80).aspx

In addition to exposing the interfaces that are explicitly implemented by a class in the managed environment, the .NET Framework supplies implementations of the COM interfaces listed in the following table on behalf of the object. A .NET class can override the default behavior by providing its own implementation of these interfaces. However, the runtime always provides the implementation for the IUnknown and IDispatch interfaces.

Interface Description
Idispatch
Provides a mechanism for late binding to type.

IerrorInfo
Provides a textual description of the error, its source, a Help file, Help context, and the GUID of the interface that defined the error (always GUID_NULL for .NET classes).

IprovideClassInfo
Enables COM clients to gain access to the ITypeInfo interface implemented by a managed class.

IsupportErrorInfo
Enables a COM client to determine whether the managed object supports the IErrorInfo interface. If so, enables the client to obtain a pointer to the latest exception object. All managed types support the IErrorInfo interface.

ItypeInfo
Provides type information for a class that is exactly the same as the type information produced by Tlbexp.exe.

Iunknown
Provides the standard implementation of the IUnknown interface with which the COM client manages the lifetime of the CCW and provides type coercion.
 

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