Toars I will smile to the world ^o^

C# Questions and Answers – 06

• Is it possible to inline assembly or IL in C# code?
  No.
• Is it possible to have different access modifiers on the get/set methods of a property?
  No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property read-only (by only providing a get accessor) and create a private/internal set method that is separate from the property.
• Is it possible to have a static indexer in C#?
  No. Static indexers are not allowed in C#.
• If I return out of a try/finally in C#, does the code in the finally-clause run?
  Yes. The code in the finally always runs. If you return out of the try block, or even if you do a “goto” out of the try, the finally block always runs:

  using System; 
  
  class main
  {
  	public static void Main()
  	{
  		try
  		{
  			Console.WriteLine("In Try block");
  			return;
  		}
  		finally
  		{
  			Console.WriteLine("In Finally block");
  		}
  	}
  }

  Both “In Try block” and “In Finally block” will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it’s a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there’s an extra store/load of the value of the expression (since it has to be computed within the try block).

• I was trying to use an “out int” parameter in one of my functions. How should I declare the variable that I am passing to it?
  You should declare the variable as an int, but when you pass it in you must specify it as ‘out’, like the following: int i; foo(out i); where foo is declared as follows: [return-type] foo(out int o) { }
• How does one compare strings in C#?
  In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings’ values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { … } Here’s an example showing how string compares work:

  using System;
  public class StringTest
  {
  	public static void Main(string[] args)
  	{
  		Object nullObj = null; Object realObj = new StringTest();
  		int i = 10;
  		Console.WriteLine("Null Object is [" + nullObj + "]\n"
  			+ "Real Object is [" + realObj + "]\n"
  			+ "i is [" + i + "]\n");
  			// Show string equality operators
  		string str1 = "foo";
  		string str2 = "bar";
  		string str3 = "bar";
  		Console.WriteLine("{0} == {1} ? {2}", str1, str2, str1 == str2 );
  		Console.WriteLine("{0} == {1} ? {2}", str2, str3, str2 == str3 );
  	}
  }

  Output:

  Null Object is []
  Real Object is [StringTest]
  i is [10]
  foo == bar ? False
  bar == bar ? True

• How do you specify a custom attribute for the entire assembly (rather than for a class)?
  Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:

  using System;
  [assembly : MyAttributeClass] class X {}

  Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs.

• How do you mark a method obsolete?

  [Obsolete] public int Foo() {...}

  or

  [Obsolete("This is a message describing why this method is obsolete")] public int Foo() {...}

  Note: The O in Obsolete is always capitalized.

• How do you implement thread synchronization (Object.Wait, Notify,and CriticalSection) in C#?
  You want the lock statement, which is the same as Monitor Enter/Exit:

  lock(obj) { // code }

  translates to

  try {
  	CriticalSection.Enter(obj);
  	// code
  }
  finally
  {
  	CriticalSection.Exit(obj);
  }

• How do you directly call a native function exported from a DLL?
  Here’s a quick example of the DllImport attribute in action:

  using System.Runtime.InteropServices; \
  class C
  {
  	[DllImport("user32.dll")]
  	public static extern int MessageBoxA(int h, string m, string c, int type);
  	public static int Main()
  	{
  		return MessageBoxA(0, "Hello World!", "Caption", 0);
  	}
  }

  This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation.

• How do I simulate optional parameters to COM calls?
  You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters.

C# Questions and Answers – 05

C# Questions and Answers – 04

• What do you know about .NET assemblies?
  Assemblies are the smallest units of versioning and deployment in the .NET application. Assemblies are also the building blocks for programs such as Web services, Windows services, serviced components, and .NET remoting applications.
• What’s the difference between private and shared assembly?
  Private assembly is used inside an application only and does not have to be identified by a strong name. Shared assembly can be used by multiple applications and has to have a strong name.
• What’s a strong name?
  A strong name includes the name of the assembly, version number, culture identity, and a public key token.
• How can you tell the application to look for assemblies at the locations other than its own install?
  Use the directive in the XML .config file for a given application.

  <probing privatePath=”c:\mylibs; bin\debug” />

  should do the trick. Or you can add additional search paths in the Properties box of the deployed application.

• How can you debug failed assembly binds?
  Use the Assembly Binding Log Viewer (fuslogvw.exe) to find out the paths searched.
• Where are shared assemblies stored?
  Global assembly cache.
• How can you create a strong name for a .NET assembly?
  With the help of Strong Name tool (sn.exe).
• Where’s global assembly cache located on the system?
  Usually C:\winnt\assembly or C:\windows\assembly.
• Can you have two files with the same file name in GAC?
  Yes, remember that GAC is a very special folder, and while normally you would not be able to place two files with the same name into a Windows folder, GAC differentiates by version number as well, so it’s possible for MyApp.dll and MyApp.dll to co-exist in GAC if the first one is version 1.0.0.0 and the second one is 1.1.0.0.
• So let’s say I have an application that uses MyApp.dll assembly, version 1.0.0.0. There is a security bug in that assembly, and I publish the patch, issuing it under name MyApp.dll 1.1.0.0. How do I tell the client applications that are already installed to start using this new MyApp.dll?
  Use publisher policy. To configure a publisher policy, use the publisher policy configuration file, which uses a format similar app .config file. But unlike the app .config file, a publisher policy file needs to be compiled into an assembly and placed in the GAC.
• What is delay signing?
  Delay signing allows you to place a shared assembly in the GAC by signing the assembly with just the public key. This allows the assembly to be signed with the private key at a later stage, when the development process is complete and the component or assembly is ready to be deployed. This process enables developers to work with shared assemblies as if they were strongly named, and it secures the private key of the signature from being accessed at different stages of development.

C# Questions and Answers – 03

• Whats an assembly?
  Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations. To the runtime, a type does not exist outside the context of an assembly.
• Describe the difference between inline and code behind - which is best in a loosely coupled solution?
  ASP.NET supports two modes of page development: Page logic code that is written inside <script runat=server> blocks within an .aspx file and dynamically compiled the first time the page is requested on the server. Page logic code that is written within an external class that is compiled prior to deployment on a server and linked "behind" the .aspx file at run time.
• Explain what a diffgram is, and a good use for one?
  A DiffGram is an XML format that is used to identify current and original versions of data elements. The DataSet uses the DiffGram format to load and persist its contents, and to serialize its contents for transport across a network connection. When a DataSet is written as a DiffGram, it populates the DiffGram with all the necessary information to accurately recreate the contents, though not the schema, of the DataSet, including column values from both the Original and Current row versions, row error information, and row order.
• Where would you use an iHTTPModule, and what are the limitations of anyapproach you might take in implementing one?
  One of ASP.NET’s most useful features is the extensibility of the HTTP pipeline, the path that data takes between client and server. You can use them to extend your ASP.NET applications by adding pre- and post-processing to each HTTP request coming into your application. For example, if you wanted custom authentication facilities for your application, the best technique would be to intercept the request when it comes in and process the request in a custom HTTP module.
• What are the disadvantages of viewstate/what are the benefits?
  No Answer Yet.
• Describe session handling in a webfarm, how does it work and what are the limits?
  No Answer Yet.
• How would you get ASP.NET running in Apache web servers - why would you even do this?
  No Answer Yet.
• Whats MSIL, and why should my developers need an appreciation of it if at all?
  When compiling to managed code, the compiler translates your source code into Microsoft intermediate language (MSIL), which is a CPU-independent set of instructions that can be efficiently converted to native code. MSIL includes instructions for loading, storing, initializing, and calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and other operations. Before code can be run, MSIL must be converted to CPU-specific code, usually by a just-in-time (JIT) compiler. Because the common language runtime supplies one or more JIT compilers for each computer architecture it supports, the same set of MSIL can be JIT-compiled and run on any supported architecture.
  When a compiler produces MSIL, it also produces metadata. Metadata describes the types in your code, including the definition of each type, the signatures of each type's members, the members that your code references, and other data that the runtime uses at execution time. The MSIL and metadata are contained in a portable executable (PE) file that is based on and extends the published Microsoft PE and common object file format (COFF) used historically for executable content. This file format, which accommodates MSIL or native code as well as metadata, enables the operating system to recognize common language runtime images. The presence of metadata in the file along with the MSIL enables your code to describe itself, which means that there is no need for type libraries or Interface Definition Language (IDL). The runtime locates and extracts the metadata from the file as needed during execution.
• In what order do the events of an ASPX page execute. As a developer is it important to undertsand these events?
  Every Page object (which your .aspx page is) has nine events, most of which you will not have to worry about in your day to day dealings with ASP.NET. The three that you will deal with the most are: Page_Init, Page_Load, Page_PreRender.
• Which method do you invoke on the DataAdapter control to load your generated dataset with data?
  

  System.Data.Common.DataAdapter.Fill(System.Data.DataSet);

  If my DataAdapter is sqlDataAdapter and my DataSet is dsUsers then it is called this way:

  sqlDataAdapter.Fill(dsUsers);

• Which template must you provide, in order to display data in a Repeater control?
  ItemTemplate
• How can you provide an alternating color scheme in a Repeater control?
  AlternatingItemTemplate Like the ItemTemplate element, but rendered for every other
  row (alternating items) in the Repeater control. You can specify a different appearance
  for the AlternatingItemTemplate element by setting its style properties.
• What property must you set, and what method must you call in your code, in order to bind the data from some data source to the Repeater control?
  You must set the DataMember property which Gets or sets the specific table in the DataSource to bind to the control and the DataBind method to bind data from a source to a server control. This method is commonly used after retrieving a data set through a database query.
• What base class do all Web Forms inherit from?
  System.Web.UI.Page
• What method do you use to explicitly kill a user’s session?
  The Abandon method destroys all the objects stored in a Session object and releases their resources.
  If you do not call the Abandon method explicitly, the server destroys these objects when the session times out.

  Syntax: Session.Abandon

• How do you turn off cookies for one page in your site?
  Use the Cookie.Discard Property which Gets or sets the discard flag set by the server. When true, this property instructs the client application not to save the Cookie on the user’s hard disk when a session ends.
• Which two properties are on every validation control?
  ControlToValidate & ErrorMessage properties
• What tags do you need to add within the asp:datagrid tags to bind columns manually?
  No Answer Yet.
• How do you create a permanent cookie?
  Setting the Expires property to MinValue means that the Cookie never expires.
• What tag do you use to add a hyperlink column to the DataGrid?
  No Answer Yet.
• What is the standard you use to wrap up a call to a Web service?
  No Answer Yet.
• Which method do you use to redirect the user to another page without performing a round trip to the client?
  Server.transfer()
• What is the transport protocol you use to call a Web service?
  SOAP. Transport Protocols: It is essential for the acceptance of Web Services that they are based on established Internet infrastructure. This in fact imposes the usage of of the HTTP, SMTP and FTP protocols based on the TCP/IP family of transports. Messaging Protocol: The format of messages exchanged between Web Services clients and Web Services should be vendor neutral and should not carry details about the technology used to implement the service. Also, the message format should allow for extensions and different bindings to specific transport protocols. SOAP and ebXML Transport are specifications which fulfill these requirements. We expect that the W3C XML Protocol Working Group defines a successor standard.
• True or False: A Web service can only be written in .NET.
  False.
• What does WSDL stand for?
  Web Services Description Language
• What property do you have to set to tell the grid which page to go to when using the Pager object?
  No Answer Yet.
• What tags do you need to add within the asp:datagrid tags to bind columns manually?
  Column tag and an ASP:databound tag.
• Which property on a Combo Box do you set with a column name, prior to setting the DataSource, to display data in the combo box?
• How is a property designated as read-only?
  In VB.NET:

  Public ReadOnly Property PropertyName As ReturnType
  	Get 		 ‘Your Property Implementation goes in here
  	End Get
  End Property

  in C#

  public returntype PropertyName
  {
  	get{
  		//property implementation goes here
  	}
  	// Do not write the set implementation
  }

• Which control would you use if you needed to make sure the values in two different controls matched?
  Use the CompareValidator control to compare the values of 2 different controls.
• True or False: To test a Web service you must create a windows application or Web application to consume this service?
  False.
• How many classes can a single .NET DLL contain?
  Unlimited.

C# Questions and Answers – 02

• Explain the differences between Server-side and Client-side code?
  Server side scripting means that all the script will be executed by the server and interpreted as needed. ASP doesn’t have some of the functionality like sockets, uploading, etc. For these you have to make a custom components usually in VB or VC++. Client side scripting means that the script will be executed immediately in the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in VBScript or JavaScript. Download time, browser compatibility, and visible code - since JavaScript and VBScript code is included in the HTML page, then anyone can see the code by viewing the page source. Also a possible security hazards for the client computer.
• What type of code (server or client) is found in a Code-Behind class?
  C#
• Should validation (did the user enter a real date) occur server-side or client-side? Why?
  Client-side validation because there is no need to request a server side date when you could obtain a date from the client machine.
• What does the "EnableViewState" property do? Why would I want it on or off?
  Enable ViewState turns on the automatic state management feature that enables server controls to re-populate their values on a round trip without requiring you to write any code. This feature is not free however, since the state of a control is passed to and from the server in a hidden form field. You should be aware of when ViewState is helping you and when it is not. For example, if you are binding a control to data on every round trip (as in the datagrid example in tip #4), then you do not need the control to maintain it’s view state, since you will wipe out any re-populated data in any case. ViewState is enabled for all server controls by default. To disable it, set the EnableViewState property of the control to false.
• What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other?
  Server.Transfer() : client is shown as it is on the requesting page only, but the all the content is of the requested page. Data can be persist across the pages using Context.Item collection, which is one of the best way to transfer data from one page to another keeping the page state alive. Response.Dedirect() :client know the physical loation (page name and query string as well). Context.Items loses the persisitance when nevigate to destination page. In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction. Besides making it difficult to maintain your transactional integrity, Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but they’re difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites, causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server without requiring a roundtrip to the client.
• Can you give an example of when it would be appropriate to use a web service as opposed to a non-serviced .NET component? When to Use Web Services:
• Communicating through a Firewall When building a distributed application with 100s/1000s of users spread over multiple locations, there is always the problem of communicating between client and server because of firewalls and proxy servers. Exposing your middle tier components as Web Services and invoking the directly from a Windows UI is a very valid option.
• Application Integration When integrating applications written in various languages and running on disparate systems. Or even applications running on the same platform that have been written by separate vendors.
• Business-to-Business Integration This is an enabler for B2B intergtation which allows one to expose vital business processes to authorized supplier and customers. An example would be exposing electronic ordering and invoicing, allowing customers to send you purchase orders and suppliers to send you invoices electronically.
• Software Reuse This takes place at multiple levels. Code Reuse at the Source code level or binary componet-based resuse. The limiting factor here is that you can reuse the code but not the data behind it. Webservice overcome this limitation. A scenario could be when you are building an app that aggregates the functionality of serveral other Applicatons. Each of these functions could be performed by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend view in a Portal or Intranet.
• When not to use Web Services: Single machine Applicatons When the apps are running on the same machine and need to communicate with each other use a native API. You also have the options of using component technologies such as COM or .NET Componets as there is very little overhead.
• Homogeneous Applications on a LAN If you have Win32 or Winforms apps that want to communicate to their server counterpart. It is much more efficient to use DCOM in the case of Win32 apps and .NET Remoting in the case of .NET Apps.
• Let’s say I have an existing application written using Visual Studio (VBInterDevand this application utilizes WindowsCOM+ transaction services. How would you approach migrating this application to .NET?
  No Answer Yet.
• Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?
  • In ADO, the in-memory representation of data is the recordset. In ADO.NET, it is the dataset. There are important differences between them.
  • A recordset looks like a single table. If a recordset is to contain data from multiple database tables, it must use a JOIN query, which assembles the data from the various database tables into a single result table. In contrast, a dataset is a collection of one or more tables. The tables within a dataset are called data tables; specifically, they are DataTable objects. If a dataset contains data from multiple database tables, it will typically contain multiple DataTable objects. That is, each DataTable object typically corresponds to a single database table or view. In this way, a dataset can mimic the structure of the underlying database. A dataset usually also contains relationships. A relationship within a dataset is analogous to a foreign-key relationship in a database —that is, it associates rows of the tables with each other. For example, if a dataset contains a table about investors and another table about each investor’s stock purchases, it could also contain a relationship connecting each row of the investor table with the corresponding rows of the purchase table. Because the dataset can hold multiple, separate tables and maintain information about relationships between them, it can hold much richer data structures than a recordset, including self-relating tables and tables with many-to-many relationships.
  • In ADO you scan sequentially through the rows of the recordset using the ADO MoveNext method. In ADO.NET, rows are represented as collections, so you can loop through a table as you would through any collection, or access particular rows via ordinal or primary key index. DataRelation objects maintain information about master and detail records and provide a method that allows you to get records related to the one you are working with. For example, starting from the row of the Investor table for "Nate Sun," you can navigate to the set of rows of the Purchase table describing his purchases. A cursor is a database element that controls record navigation, the ability to update data, and the visibility of changes made to the database by other users. ADO.NET does not have an inherent cursor object, but instead includes data classes that provide the functionality of a traditional cursor. For example, the functionality of a forward-only, read-only cursor is available in the ADO.NET DataReader object. For more information about cursor functionality, see Data Access Technologies.
  • Minimized Open Connections: In ADO.NET you open connections only long enough to perform a database operation, such as a Select or Update. You can read rows into a dataset and then work with them without staying connected to the data source. In ADO the recordset can provide disconnected access, but ADO is designed primarily for connected access. There is one significant difference between disconnected processing in ADO and ADO.NET. In ADO you communicate with the database by making calls to an OLE DB provider. In ADO.NET you communicate with the database through a data adapter (an OleDbDataAdapter, SqlDataAdapter, OdbcDataAdapter, or OracleDataAdapter object), which makes calls to an OLE DB provider or the APIs provided by the underlying data source. The important difference is that in ADO.NET the data adapter allows you to control how the changes to the dataset are transmitted to the database — by optimizing for performance, performing data validation checks, or adding any other extra processing. Data adapters, data connections, data commands, and data readers are the components that make up a .NET Framework data provider. Microsoft and third-party providers can make available other .NET Framework data providers that can be integrated into Visual Studio.
  • Sharing Data Between Applications. Transmitting an ADO.NET dataset between applications is much easier than transmitting an ADO disconnected recordset. To transmit an ADO disconnected recordset from one component to another, you use COM marshalling. To transmit data in ADO.NET, you use a dataset, which can transmit an XML stream.
  • Richer data types.COM marshalling provides a limited set of data types — those defined by the COM standard. Because the transmission of datasets in ADO.NET is based on an XML format, there is no restriction on data types. Thus, the components sharing the dataset can use whatever rich set of data types they would ordinarily use.
  • Performance. Transmitting a large ADO recordset or a large ADO.NET dataset can consume network resources; as the amount of data grows, the stress placed on the network also rises. Both ADO and ADO.NET let you minimize which data is transmitted. But ADO.NET offers another performance advantage, in that ADO.NET does not require data-type conversions. ADO, which requires COM marshalling to transmit records sets among components, does require that ADO data types be converted to COM data types.
  • Penetrating Firewalls.A firewall can interfere with two components trying to transmit disconnected ADO recordsets. Remember, firewalls are typically configured to allow HTML text to pass, but to prevent system-level requests (such as COM marshalling) from passing.
• Can you give an example of what might be best suited to place in the Application_Start and Session_Start subroutines?
  The Application_Start event is guaranteed to occur only once throughout the lifetime of the application. It’s a good place to initialize global variables. For example, you might want to retrieve a list of products from a database table and place the list in application state or the Cache object. SessionStateModule exposes both Session_Start and Session_End events.
• If I’m developing an application that must accomodate multiple security levels though secure login and my ASP.NET web appplication is spanned across three web-servers (using round-robbin load balancing) what would be the best approach to maintain login-in state for the users?
  No Answer Yet.
• What are ASP.NET Web Forms? How is this technology different than what is available though ASP?
  Web Forms are the heart and soul of ASP.NET. Web Forms are the User Interface (UI) elements that give your Web applications their look and feel. Web Forms are similar to Windows Forms in that they provide properties, methods, and events for the controls that are placed onto them. However, these UI elements render themselves in the appropriate markup language required by the request, e.g. HTML. If you use Microsoft Visual Studio .NET, you will also get the familiar drag-and-drop interface used to create your UI for your Web application.
• How does VB.NET/C# achieve polymorphism?
  By using Abstract classes/functions.
• Can you explain what inheritance is and an example of when you might use it?
  Inheritance is a fundamental feature of an object oriented system and it is simply the ability to inherit data and functionality from a parent object. Rather than developing new objects from scratch, new code can be based on the work of other programmers, adding only new features that are needed.
• How would you implement inheritance using VB.NET/C#?
  When we set out to implement a class using inheritance, we must first start with an existing class from which we will derive our new subclass. This existing class, or base class, may be part of the .NET system class library framework, it may be part of some other application or .NET assembly, or we may create it as part of our existing application. Once we have a base class, we can then implement one or more subclasses based on that base class. Each of our subclasses will automatically have all of the methods, properties, and events of that base class ? including the implementation behind each method, property, and event. Our subclass can add new methods, properties, and events of its own - extending the original interface with new functionality. Additionally, a subclass can replace the methods and properties of the base class with its own new implementation - effectively overriding the original behavior and replacing it with new behaviors. Essentially inheritance is a way of merging functionality from an existing class into our new subclass. Inheritance also defines rules for how these methods, properties, and events can be merged.