C# Interview Questions and Answers

1. What’s the implicit name of the parameter that gets passed into the class’ set method?
   Value, and its datatype depends on whatever variable we’re changing.
2. How do you inherit from a class in C#?
   Place a colon and then the name of the base class. Notice that it’s double colon in C++.
3. Does C# support multiple inheritance?
   No, use interfaces instead.
4. When you inherit a protected class-level variable, who is it available to?
   Classes in the same namespace.
5. Are private class-level variables inherited?
   Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.
6. Describe the accessibility modifier protected internal.
   It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
7. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write? Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.
8. What’s the top .NET class that everything is derived from?
   System.Object.
9. How’s method overriding different from overloading?
   When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.
10. What does the keyword virtual mean in the method definition?
    The method can be over-ridden.
11. Can you declare the override method static while the original method is non-static?
    No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
12. Can you override private virtual methods?
    No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
13. Can you prevent your class from being inherited and becoming a base class for some other classes?
    Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.
14. Can you allow class to be inherited, but prevent the method from being over-ridden?
    Yes, just leave the class public and make the method sealed.
15. What’s an abstract class?
    A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.
16. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
    When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.
17. What’s an interface class?
    It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
18. Why can’t you specify the accessibility modifier for methods inside the interface?
    They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
19. Can you inherit multiple interfaces?
    Yes, why not.
20. And if they have conflicting method names?
    It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
21. What’s the difference between an interface and abstract class?
    In the interface all methods must be abstract; in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.
22. How can you overload a method?
    Different parameter data types, different number of parameters, different order of parameters.
23. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor?
    Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
24. What’s the difference between System.String and System.StringBuilder classes?
    System.String is immutable; System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.
25. 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.
26. Can you store multiple data types in System.Array?
    No.
27. 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.
28. How can you sort the elements of the array in descending order?
    By calling Sort() and then Reverse() methods.
29. What’s the .NET datatype that allows the retrieval of data by a unique key?
    HashTable.
30. What’s class SortedList underneath?
    A sorted HashTable.
31. Will finally block get executed if the exception had not occurred?
    Yes.
32. 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 {}.
33. 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.
34. 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.
35. What’s a delegate?
    A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
36. What’s a multicast delegate?
    It’s a delegate that points to and eventually fires off several methods.
37. 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.
38. What are the ways to deploy an assembly?
    An MSI installer, a CAB archive, and XCOPY command.
39. 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.
40. What namespaces are necessary to create a localized application?
    System.Globalization, System.Resources.
41. What’s the difference between // comments, /* */ comments and /// comments?
    Single-line, multi-line and XML documentation comments.
42. How do you generate documentation from the C# file commented properly with a command-line compiler?
    Compile it with a /doc switch.
43. What’s the difference between <c> and <code> XML documentation tag?
    Single line code example and multiple-line code example.
44. Is XML case-sensitive?
    Yes, so <Student> and <student> are different elements.
45. 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.
46. 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.
47. 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.
48. 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.
49. 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.
50. Where is the output of TextWriterTraceListener redirected?
    To the Console or a text file depending on the parameter passed to the constructor.
51. How do you debug an ASP.NET Web application?
    Attach the aspnet_wp.exe process to the DbgClr debugger.
52. 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).
53. 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.
54. Explain the three services model (three-tier application).
    Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
55. 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.
56. 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.
57. 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%’.
58. 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).
59. What connections does Microsoft SQL Server support?
    Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
60. 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.
61. Why would you use untrusted verificaion?
    Web Services might use it, as well as non-Windows applications.
62. What does the parameter Initial Catalog define inside Connection String?
    The database name to connect to.
63. What’s the data provider name to connect to Access database?
    Microsoft.Access.
64. What does Dispose method do with the connection object?
    Deletes it from the memory.
65. 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# developer interview questions

A representative of a high-tech company in United Kingdom sent this in today noting that the list was used for interviewing a C# .NET developer. Any corrections and suggestions would be forwarded to the author. I won’t disclose the name of the company, since as far as I know they might still be using this test for prospective employees. Correct answers are in green color.

1) The C# keyword .int. maps to which .NET type?

1. System.Int16

2. System.Int32

3. System.Int64

4. System.Int128

2) Which of these string definitions will prevent escaping on backslashes in C#?

1. string s = #.n Test string.;

2. string s = ..n Test string.;

3. string s = @.n Test string.;

4. string s = .n Test string.;

3) Which of these statements correctly declares a two-dimensional array in C#?

1. int[,] myArray;

2. int[][] myArray;

3. int[2] myArray;

4. System.Array[2] myArray;

4) If a method is marked as protected internal who can access it?

1. Classes that are both in the same assembly and derived from the declaring class.

2. Only methods that are in the same class as the method in question.

3. Internal methods can be only be called using reflection.

4. Classes within the same assembly, and classes derived from the declaring class.

5) What is boxing?

a) Encapsulating an object in a value type.

b) Encapsulating a copy of an object in a value type.

c) Encapsulating a value type in an object.

d) Encapsulating a copy of a value type in an object.

6) What compiler switch creates an xml file from the xml comments in the files in an assembly?

1. /text

2. /doc

3. /xml

4. /help

7) What is a satellite Assembly?

1. A peripheral assembly designed to monitor permissions requests from an application.

2. Any DLL file used by an EXE file.

3. An assembly containing localized resources for another assembly.

4. An assembly designed to alter the appearance or .skin. of an application.

8) What is a delegate?

1. A strongly typed function pointer.

2. A light weight thread or process that can call a single method.

3. A reference to an object in a different process.

4. An inter-process message channel.

9) How does assembly versioning in .NET prevent DLL Hell?

1. The runtime checks to see that only one version of an assembly is on the machine at any one time.

2. .NET allows assemblies to specify the name AND the version of any assemblies they need to run.

3. The compiler offers compile time checking for backward compatibility.

4. It doesn.t.

10) Which .Gang of Four. design pattern is shown below?

public class A {

    private A instance;

    private A() {

    }

    public
static A Instance {

        get

        {

            if ( A == null )

                A = new A();

            return instance;

        }

    }

}

1. Factory

2. Abstract Factory

3. Singleton

4. Builder

11) In the NUnit test framework, which attribute must adorn a test class in order for it to be picked up by the NUnit GUI?

1. TestAttribute

2. TestClassAttribute

3. TestFixtureAttribute

4. NUnitTestClassAttribute

12) Which of the following operations can you NOT perform on an ADO.NET DataSet?

1. A DataSet can be synchronised with the database.

2. A DataSet can be synchronised with a RecordSet.

3. A DataSet can be converted to XML.

4. You can infer the schema from a DataSet.

13) In Object Oriented Programming, how would you describe encapsulation?

1. The conversion of one type of object to another.

2. The runtime resolution of method calls.

3. The exposition of data.

4. The separation of interface and implementation.

Posted in: Interview Questions | Tags: interview questions and answers questions interview answers q&a .net c# c sharp sql server private derive overloading definition static abstract interface base inherited inherit variable acid trusted immediate window data provider ado.net

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how to set Client IDs in asp.net 4.0

The new ClientIDMode property addresses a long-standing issue in ASP.NET, namely how controls create the id attribute for elements that they render. Knowing the id attribute for rendered elements is important if your application includes client script that references these elements.

The id attribute in HTML that is rendered for Web server controls is generated based on the ClientID property of the control. The algorithm up to now for generating the id attribute from the ClientID property has been to concatenate the naming container (if any) with the ID, and in the case of repeated controls (as in data controls), to add a prefix and a sequential number. While this has always guaranteed that the IDs of controls in the page are unique, the algorithm has resulted in control IDs that were not predictable, and were therefore difficult to reference in client script.

The new ClientIDMode property lets you specify more precisely how the client ID is generated for controls. You can set the ClientIDMode property for any control, including for the page. Possible settings are the following:

· AutoID – This is equivalent to the algorithm for generating ClientID property values that was used in earlier versions of ASP.NET.

· Static – This specifies that the ClientID value will be the same as the ID without concatenating the IDs of parent naming containers. This can be useful in Web user controls. Because a Web user control can be located on different pages and in different container controls, it can be difficult to write client script for controls that use the AutoID algorithm because you cannot predict what the ID values will be.

· Predictable – This option is primarily for use in data controls that use repeating templates. It concatenates the ID properties of the control's naming containers, but generated ClientID values do not contain strings like "ctlxxx". This setting works in conjunction with the ClientIDRowSuffix property of the control. You set the ClientIDRowSuffix property to the name of a data field, and the value of that field is used as the suffix for the generated ClientID value. Typically you would use the primary key of a data record as the ClientIDRowSuffix value.

· Inherit – This setting is the default behavior for controls; it specifies that a control's ID generation is the same as its parent.

You can set the ClientIDMode property at the page level. This defines the default ClientIDMode value for all controls in the current page.

The default ClientIDMode value at the page level is AutoID, and the default ClientIDMode value at the control level is Inherit. As a result, if you do not set this property anywhere in your code all controls will default to the AutoID algorithm.

You set the page-level value in the @ Page directive, as shown in the following example:

<%@ Page Language="C#" AutoEventWireup="true"

CodeFile="Default.aspx.cs"

Inherits="_Default"

ClientIDMode="Predictable" %>

You can also set the ClientIDMode value in the configuration file, either at the machine level or at the application level. This defines the default ClientIDMode setting for all controls in all pages in the application. If you set the value at the machine level, it defines the default ClientIDMode setting for all Web sites on that computer. The following example shows the ClientIDMode setting in the configuration file:

<system.web>

<pages clientIDMode="Predictable"></pages>

</system.web>

As noted earlier, the value of the ClientID property is derived from the naming container for a control’s parent. In some scenarios, such as when you are using master pages, controls can end up with IDs like those in the following rendered HTML:

<div id="ctl00_ContentPlaceHolder1_ParentPanel">

<div id="ctl00_ContentPlaceHolder1_ParentPanel_NamingPanel1">

<input name="ctl00$ContentPlaceHolder1$ParentPanel$NamingPanel1$TextBox1"

type="text" value="Hello!"

id="ctl00_ContentPlaceHolder1_ParentPanel_NamingPanel1_TextBox1" />

</div>

Even though the input element (from a TextBox control) shown in the markup is only two naming containers deep in the page (the nested ContentPlaceholder controls), because of the way master pages are processed, the end result is a control ID like the following:

ctl00_ContentPlaceHolder1_ParentPanel_NamingPanel1_TextBox1

This is a long ID. It is guaranteed to be unique in the page, but is unnecessarily long for most purposes. Imagine that you want to reduce the length of the rendered ID, and to have more say in how the ID is generated (for example, you want to eliminate “ctlxxx” prefixes). The easiest way to achieve this is by setting the ClientIDMode property as shown in the following example:

<tc:NamingPanel runat="server" ID="ParentPanel" ClientIDMode="Static">

<tc:NamingPanel runat="server" ID="NamingPanel1" ClientIDMode="Predictable">

<asp:TextBox ID="TextBox1" runat="server" Text="Hello!"></asp:TextBox>

</tc:NamingPanel>

</tc:NamingPanel>

In this sample, the ClientIDMode property is set to Static for the outermost NamingPanel element, and set to Predictable for the inner NamingControl element. These settings result in the following markup (the rest of the page and the master page is assumed to be the same as in the previous example):

<div id="ParentPanel">

<div id="ParentPanel_NamingPanel1">

<input name="ctl00$ContentPlaceHolder1$ParentPanel$NamingPanel1$TextBox1"

type="text" value="Hello!" id="ParentPanel_NamingPanel1_TextBox1" />

</div>

The Static setting has the effect of resetting the naming hierarchy for any controls inside the outermost NamingPanel element, and of eliminating the ContentPlaceHolder and MasterPage IDs from the generated ID. (Note that the name attribute of rendered elements is unaffected, so that the normal ASP.NET functionality is retained for events, view state, and so on.) A nice side effect of resetting the naming hierarchy is that even if you move the markup for the NamingPanel elements to a different ContentPlaceholder control, the rendered client IDs remain the same.

Note   It is up to you to make sure that the rendered control IDs are unique. If they are not, it can break any functionality that requires unique IDs for individual HTML elements, such as the client document.getElementById function.

Creating Predictable Client IDs in Data-Bound Controls

The ClientID values that are generated for controls in a data-bound list control by the legacy algorithm can be long and are not really predictable. The ClientIDMode functionality can help you have more control over how these IDs are generated.

Look at the following markup, which includes a ListView control:

<asp:ListView ID="ListView1" runat="server" DataSourceID="SqlDataSource1"

OnSelectedIndexChanged="ListView1_SelectedIndexChanged"

ClientIDMode="Predictable"

RowClientIDRowSuffix="ProductID">

</asp:ListView>

In the previous example, the ClientIDMode and RowClientIDRowSuffix properties are set in markup. The ClientIDRowSuffix property can be used only in data-bound controls, and its behavior differs depending on which control you are using. The differences are these:

· GridView control — You can specify the name of one or more columns in the data source, which are combined at run time to create the client IDs. For example, if you set RowClientIDRowSuffix to “ProductName, ProductId”, control IDs for rendered elements will have a format like the following:

rootPanel_GridView1_ProductNameLabel_Chai_1

· ListView control — You can specify a single column in the data source that is appended to the client ID. For example, if you set ClientIDRowSuffix to “ProductName”, the rendered control IDs will have a format like the following:

rootPanel_ListView1_ProductNameLabel_1

In this case the trailing 1 is derived from the product ID of the current data item.

· Repeater control— This control does not support the ClientIDRowSuffix property. In a Repeater control, the index of the current row is used. When you use ClientIDMode="Predictable" with a Repeater control, client IDs are generated that have the following format:

Repeater1_ProductNameLabel_0

The trailing 0 is the index of the current row.

The FormView and DetailsView controls do not display multiple rows, so they do not support the ClientIDRowSuffix property.

Posted in: asp.net | Tags: asp.net 4.0 clientid static clientidrowsuffix clientidmode parentpanel autoeventwireup predictable

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