COM, DCOM +DCOM+

COM, DCOM +DCOM+

Question:-Can it is possible to use COM objects from a .NET Framework program ?
Answer: :- I think yes COM component which we have deployed today can be used from managed code, and in common cases the its adopt automatic. To access com component from the .NET Framework we use runtime callable wrapper (RCW). This wrapper turns the COM interfaces exposed by the COM component into .NET Framework-compatible interfaces. For OLE automation interfaces, the RCW can be generated automatically from a type library. But for non-OLE automation interfaces, a developer may have to write a custom RCW and then manually map types that is exposed by the COM interface to .NET Framework-compatible types.

Question:-What is Monikers when using COM ?
Answer: Clients always require a easy way to reconnect the same process where he is on last time or we can say that exact same state at a later point in time. This support is provided via "monikers". A moniker is a COM object that helps in this task because its knows how to create and initialize the content of a single COM object instance. A moniker can be asked to bind to the COM object it showing, so a COM object on specific machine on the network, or a group of cells inside a spreadsheet.

Question:-Explain Transaction with COM+ Components?
Answer: Transaction consists of group of task bind in a single execution unit .When a transaction starts with specific task it is completed when all the statement in units are completed if any one produce error it will Rollback.So transaction have only two result Success and failure.
On the other hand COM+ components need code to transaction.Because it will automatically participate in transaction.Its not require any explicit code to specify the start and end of transaction.when we create an object of COM+ it is activated with BeginTransaction with COM+ services provides.And this object is deactivated using CommitTransaction or AbortTransaction method.


Question:-How COM+ Component adopt security?
Answer: To reduce complexity COM+ used or provides role-based security service that's helps in middle-tier components.There are two types of role-based security.
(1)Declaractive
(2)Programmatic
When we applied and configure security without using an explicit programming interface is known as declartive security settings. On the other hand there are some situation when work load is heavy and secuirty is must and exchange of data accross the network and security measure should be taken with programming interface and it is known as programmactic secrity.

Question:-What are the COM Component in .Net?
Answer: .Net not helps in creation of COM components and provides a different solution for making reusable components through Assemblies.There are many COM components present which our .Net application might need to use..Net provides an extremely simple approach to achieve this.
We use com by ‘Wrapper Classes’ and ‘Proxy Components’. .Net wraps the COM component into .Net assembly technically called ‘Runtime Callable Wrapper’ or RCW. Then u can call and use your COM component just as a .Net (or C#, if u are using C#) Assembly.

Question:-Whats the relation between COM/DCOM ?
Answer: DCOM is an extended to COM that allows network-based component interaction. Because COM only ability that processes can run on the same machine but in different address spaces, the DCOM extension allows across a network. DCOM components can helpfull on variety of platforms . we can also say that COM and DCOM is single technology that provides a many services for component interaction, some specific tasks are component integration on a single platform,component interaction across heterogeneous networks.COM and its DCOM extensions are merged into a single runtime.

Question:-Which namespace do the classes, allowing you to support COM functionality, are located?
Answer: System.EnterpriseServices

Question:- How do you make a NET component talk to a COM component?
Answer: To enable the communication between COM and .NET components, the .NET Framework generates a COM Callable Wrapper (CCW). The CCW enables communication between the calling COM code and the managed code. It also handles conversion between the data types, as well as other messages between the COM types and the .NET types.

Question:-How do you generate an RCW from a COM object?
Answer: Use the Type Library Import utility shipped with SDK. tlbimp COMobject.dll /out:.NETobject.dll or reference the COM library from Visual Studio in your project.

Question:-I can’t import the COM object that I have on my machine. Did you write that object?
Answer:You can only import your own objects. If you need to use a COM component from another developer, you should obtain a Primary Interop Assembly (PIA) from whoever authored the original object.

Question:-How do you call unmanaged methods from your .NET code through PInvoke?
Answer: Supply a DllImport attribute. Declare the methods in your .NET code as static extern. Do not implement the methods as they are implemented in your unmanaged code, you’re just providing declarations for method signatures.

Question:- Can you retrieve complex data types like structs from the PInvoke calls?
Answer: Yes, just make sure you re-declare that struct, so that managed code knows what to do with it.

Question:- I want to expose my .NET objects to COM objects. Is that possible?
Answer: Yes, but few things should be considered first. Classes should implement interfaces explicitly. Managed types must be public. Methods, properties, fields, and events that are exposed to COM must be public. Types must have a public default constructor with no arguments to be activated from COM. Types cannot be abstract.

Question:-Can you inherit a COM class in a .NET application?
Answer: The .NET Framework extends the COM model for reusability by adding implementation inheritance. Managed types can derive directly or indirectly from a COM coclass; more specifically, they can derive from the runtime callable wrapper generated by the runtime. The derived type can expose all the method and properties of the COM object as well as methods and properties implemented in managed code. The resulting object is partly implemented in managed code and partly implemented in unmanaged code.

Question:-Suppose I call a COM object from a .NET applicaiton, but COM object throws an error. What happens on the .NET end?
Answer: COM methods report errors by returning HRESULTs; .NET methods report them by throwing exceptions. The runtime handles the transition between the two. Each exception class in the .NET Framework maps to an HRESULT.