COM - 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.

DOT NET FRAME WORK

DOT NET FRAME WORK


(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL
(Common Intermediate Language). All .NET source code is compiled to IL. This IL is then converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

What is a CLR?

Full form of CLR is Common Language Runtime and it forms the heart of the .NET framework.
All Languages have runtime and its the responsibility of the runtime to take care of the code execution of the program. For example VC++ has MSCRT40.DLL,VB6 has MSVBVM60.DLL,
Java has Java Virtual Machine etc. Similarly .NET has CLR. Following are the responsibilities of
CLR.

√ Garbage Collection :- CLR automatically manages memory thus eliminating memory leaks. When objects are not referred GC automatically releases those memories thus providing efficient memory management.

√ Code Access Security :- CAS grants rights to program depending on the security
configuration of the machine. Example the program has rights to edit or create
a new file but the security configuration of machine does not allow the program
to delete a file. CAS will take care that the code runs under the environment of
machines security configuration.

√ Code Verification :- This ensures proper code execution and type safety while
the code runs. It prevents the source code to perform illegal operation such as
accessing invalid memory locations etc.

IL( Intermediate language )-to-native translators and optimizer’s :- CLR uses
JIT and compiles the IL code to machine code and then executes. CLR also
determines depending on platform what is optimized way of running the IL
code.

What is a CTS?

In order that two language communicate smoothly CLR has CTS (Common Type System).

Example

in VB you have “Integer” and in C++ you have “long” these datatypes are not compatible so the
interfacing between them is very complicated. In order to able that two different languages can communicate Microsoft introduced Common Type System. So “Integer” datatype in VB6 and
“int” datatype in C++ will convert it to System.int32 which is datatype of CTS. CLS which is
covered in the coming question is subset of CTS.

Note: If you have undergone COM programming period interfacing VB6 application with VC++ application was a real pain as the datatype of both languages did not have a common ground where they can come and interface, by having CTS interfacing is smooth.

What is a CLS(Common Language Specification)?

This is a subset of the CTS which all .NET languages are expected to support. It was always a dream of Microsoft to unite all different languages in to one umbrella and CLS is one step towards that. Microsoft has defined CLS which are nothing but guidelines that language to follow
so that it can communicate with other .NET languages in a seamless manner.

What is a Managed Code?

Managed code runs inside the environment of CLR i.e. .NET runtime. In short all IL are managed code. But if you are using some third party software example VB6 or VC++ component they are unmanaged code as .NET runtime (CLR) does not have control over the source code execution of the language.