AppDomain Class

Application domains, which are represented by AppDomain objects, help provide isolation, unloading, and security boundaries for executing managed code.

Multiple application domains can run in a single process; however, there is not a one-to-one correlation between application domains and threads. Several threads can belong to a single application domain, and while a given thread is not confined to a single application domain, at any given time, a thread executes in a single application domain.

Application domains are created using the CreateDomain method. AppDomain instances are used to load and execute assemblies (Assembly). When an AppDomain is no longer in use, it can be unloaded.

The AppDomain class implements a set of events that enable applications to respond when an assembly is loaded, when an application domain will be unloaded, or when an unhandled exception is thrown.

Delegates in C#

Introduction


Delegates in C# are like functions pointers in C/C++. A multi cast delegate can refer to several methods. A delegate can be used to invoke a method, the call to which can only be resolved or determined at runtime. This article discusses what delegates are and how they can be used in C# with lucid code examples.

What are delegates and why are they required?
Delegates are function pointers in C# that are managed and type safe and can refer to one or more methods that have identical signatures. Delegates in C# are reference types. They are type safe, managed function pointers in C# that can be used to invoke a method that the delegate refers to. The signature of the delegate should be the same as the signature of the method to which it refers. According to MSDN, "A delegate in C# is similar to a function pointer in C or C++. Using a delegate allows the programmer to encapsulate a reference to a method inside a delegate object. The delegate object can then be passed to code which can call the referenced method, without having to know at compile time which method will be invoked. Unlike function pointers in C or C++, delegates are object-oriented, type-safe, and secure."

C# provides support for Delegates through the class called Delegate in the System namespace. Delegates are of two types.

· Single-cast delegates

· Multi-cast delegates

A Single-cast delegate is one that can refer to a single method whereas a Multi-cast delegate can refer to and eventually fire off multiple methods that have the same signature.

The signature of a delegate type comprises are the following.

· The name of the delegate

· The arguments that the delegate would accept as parameters

· The return type of the delegate

A delegate is either public or internal if no specifier is included in its signature. Further, you should instantiate a delegate prior to using the same.


reference: http://aspalliance.com/1228_Working_with_Delegates_in_C#top
reference: http://www.akadia.com/services/dotnet_delegates_and_events.html

Advanced C# interview questions .NET

http://www.techinterviews.com/?p=57

http://blogs.crsw.com/mark/articles/252.aspx

1. What’s the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.
2. Can you store multiple data types in System.Array? No.
3. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()? The first one performs a deep copy of the array, the second one is shallow.
4. How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods.
5. What’s the .NET datatype that allows the retrieval of data by a unique key? HashTable.
6. What’s class SortedList underneath? A sorted HashTable.
7. Will finally block get executed if the exception had not occurred? Yes.
8. What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception? A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.
9. Can multiple catch blocks be executed? No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.
10. Why is it a bad idea to throw your own exceptions? Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.
11. What’s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
12. What’s a multicast delegate? It’s a delegate that points to and eventually fires off several methods.
13. How’s the DLL Hell problem solved in .NET? Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.
14. What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command.
15. What’s a satellite assembly? When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.
16. What namespaces are necessary to create a localized application? System.Globalization, System.Resources.
17. What’s the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments.
18. How do you generate documentation from the C# file commented properly with a command-line compiler? Compile it with a /doc switch.
19. What’s the difference between and XML documentation tag? Single line code example and multiple-line code example.
20. Is XML case-sensitive? Yes, so and are different elements.
21. What debugging tools come with the .NET SDK? CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.
22. What does the This window show in the debugger? It points to the object that’s pointed to by this reference. Object’s instance data is shown.
23. What does assert() do? In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.
24. What’s the difference between the Debug class and Trace class? Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.
25. Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.
26. Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.
27. How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger.
28. What are three test cases you should go through in unit testing? Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).
29. Can you change the value of a variable while debugging a C# application? Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.
30. Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
31. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET? SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.
32. What’s the role of the DataReader class in ADO.NET connections? It returns a read-only dataset from the data source when the command is executed.
33. What is the wildcard character in SQL? Let’s say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve ‘La%’.
34. Explain ACID rule of thumb for transactions. Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).
35. What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
36. Which one is trusted and which one is untrusted? Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.
37. Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications.
38. What does the parameter Initial Catalog define inside Connection String? The database name to connect to.
39. What’s the data provider name to connect to Access database? Microsoft.Access.
40. What does Dispose method do with the connection object? Deletes it from the memory.
41. What is a pre-requisite for connection pooling? Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.

C# Interview Questions

C# Question
1. What is the namespace used to access the information about the Assembly in C#?
2. What are indexes in C# (do not confuse with indexes in sqlserver).
3. What are indexes in C# (do not confuse with indexes in sqlserver).
4. what is protected in C#?
5. what is difference between read only and constant statement?
6. What is Internal? & protected internal?
7. How to raise an event and pass information from a user control
8. Usercontrols in Winforms
9. Private Constructor, what it is? Its use & Advantage?
10. What is Static Constructor? It’s use? Will it executed when we call the static method each time or only at 1st time?
11. What is Custom attribute? How to create? Namespace to access it? If I'm having custom attribute in an assembly, how to say that name in the code?
12. What is the usage of “internal” access specifier
13. What is Event Delegate, clear syntax for writing a event delegate
14. What is static constructor, when it will be fired? and what is its use
15. Can you create instance of a class which has Private Constructor
16. Question related to Access modifiers
17. OOPS Methodology in C#
18. Mechanism of a Garbage Collector
19. What are OOPS Concepts?
20. What is the Difference between a Structure and a Class?
21. What is an Interface? What are the available Interfaces in COM?
22. What are Sealed Classes in C#?
23. How to Override a function in C#?
24. Design related questions, C#, OOPS
25. What r the access specifiers in C#
26. Difference between Protected & Protected Internal
27. What specifier u used when u want to create once and use it
28. When to use Interface & Abstract ,give the exact scenario with example
29. Difference between static constructor / type constructor
30. I have 3 overloaded constructors in my class. In order to avoid making instance of the class do I need to make all constructors to private? Overloaded constructor will call default constructor internally?
31. In which Scenario you will go for Interface or Abstract Class?
32. Difference between static constructor / type constructor
33. What is Type Constructor and Instance Constructor (Static Constructor and Instance Constructor)
34. What are the Access Specifiers in C#
35. Have a look at the following class Public class Employee { private int Emplyeeage 25; private String employeename=”venkat” public static void displayempdetail() { MessageBox.Show(Employeeage+” “+EmployeeName) } public static void displayempdetail1() { Employee e1=new Employee(); e1.anotherFun(); } public void anotherFun() { MessageBox.Show(Employeeage+” “+EmployeeName) } } What would be the result if we call Employee.displayempdetail() ? Will It work
36. What the attributes in a Function Signature?
37. What access specifiers available in c#
38. Explain about Protected access and protected internal access
39. Difference between type constructor and instance constructor
40. In which cases you use Override and new base.
41. What data providers available in .net to connect to database and what are all things
42. What is Inheritance?
43. Difference between public and protected?
44. What is Overriding?
45. What is Overloading?
46. What is managed code & Unmanaged code?
47. C# language feature

Finding calling method using reflection

Add namespaces:

using System.Diagnostics;
using System.Reflection;

There's probably a more elegant way to do this, but I wanted to find out which method had called the current method for logging. For example, I am calling a method in my DAO and i want to know which method from my Service layer called it...the Stack trace caught during an exception cuts me off and I could only find snippets of getting the current method name for logging purposes.

So, here's a method I drummed up to get the name of the calling-calling method:

private string GetPreviousMethodName(MethodBase currentMethod)

{

string methodName = string.Empty;

try

{

StackTrace sTrace = new System.Diagnostics.StackTrace(true);

//loop through all the stack frames

for (Int32 frameCount = 0; frameCount <>

{

StackFrame sFrame = sTrace.GetFrame(frameCount);

System.Reflection.MethodBase thisMethod = sFrame.GetMethod();

//If the Type in the frame is the type that is being searched

if (thisMethod == currentMethod)

{

if (frameCount + 1 <= sTrace.FrameCount)

{

StackFrame prevFrame = sTrace.GetFrame(frameCount + 1);

System.Reflection.MethodBase prevMethod = prevFrame.GetMethod();

methodName = prevMethod.ReflectedType + "." + prevMethod.Name;

//get the method and its parameter info

//then exit out of the for loop

}

break;

}

}

}

catch (Exception)

{

//swallow all exceptions this may encounter...this is informational and mroe for convenience anyways

return string.Empty;

}

return methodName;

}

Reflection in .Net

How to use Reflection in our applications?

System.Reflection namespace contains all the Reflection related classes. These classes are used to get information from any of the class under .NET framework. The Type class is the root of all reflection operations. Type is an abstract base class that acts as means to access metadata though the reflection classes. Using Type object, any information related to methods, implementation details and manipulating information can be obtained. The types include the constructors, methods, fields, properties, and events of a class, along with this the module and the assembly in which these information are present can be accessed and manipulated easily.


Namespace Required : using System.Reflection;

get Methods Inside the Object

Type type = typeof(Employee);
MemberInfo[] m = type.GetMethods();
foreach (MemberInfo m1 in m)
{
MessageBox.show(m1.Name);
}


get Constructors Inside the Object

Type type = typeof(Employee);
MemberInfo[] m = type.GetConstructors();
foreach (MemberInfo m1 in m)
{
MessageBox.show(m1.Name);
}

Reference : http//aspalliance.com/778