Questions

How do you handle data concurrency in .NET ?
One of the key features of the ADO.NET DataSet is that it can be a self-contained and disconnected data store. It can contain the schema and data from several rowsets in DataTable objects as well as information about how to relate the DataTable objects-all in memory. The DataSet neither knows nor cares where the data came from, nor does it need a link to an underlying data source. Because it is data source agnostic you can pass the DataSet around networks or even serialize it to XML and pass it across the Internet without losing any of its features. However, in a disconnected model, concurrency obviously becomes a much bigger problem than it is in a connected model.

In this column, I’ll explore how ADO.NET is equipped to detect and handle concurrency violations. I’ll begin by discussing scenarios in which concurrency violations can occur using the ADO.NET disconnected model. Then I will walk through an ASP.NET application that handles concurrency violations by giving the user the choice to overwrite the changes or to refresh the out-of-sync data and begin editing again. Because part of managing an optimistic concurrency model can involve keeping a timestamp (rowversion) or another type of flag that indicates when a row was last updated, I will show how to implement this type of flag and how to maintain its value after each database update.

What is WSDL?

WSDL is the Web Service Description Language, and it is implemented as a specific XML vocabulary. While it’s very much more complex than what can be described here, there are two important aspects to WSDL with which you should be aware. First, WSDL provides instructions to consumers of Web Services to describe the layout and contents of the SOAP packets the Web Service intends to issue. It’s an interface description document, of sorts. And second, it isn’t intended that you read and interpret the WSDL. Rather, WSDL should be processed by machine, typically to generate proxy source code (.NET) or create dynamic proxies on the fly (the SOAP Toolkit or Web Service Behavior).

What does AspCompat=”true” mean and when should I use it?

AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false but should be set to true in any ASPX file that creates apartment-threaded COM objects–that is, COM objects registered ThreadingModel=Apartment. That includes all COM objects written with Visual Basic 6.0. AspCompat should also be set to true (regardless of threading model) if the page creates COM objects that access intrinsic ASP objects such as Request and Response. The following directive sets AspCompat to true

What is Web Gardening? How would using it affect a design?

The Web Garden Model: The Web garden model is configurable through the section of the machine.config file. Notice that the section is the only configuration section that cannot be placed in an application-specific web.config file. This means that the Web garden mode applies to all applications running on the machine. However, by using the node in the machine.config source, you can adapt machine-wide settings on a per-application basis.
Two attributes in the section affect the Web garden model. They are webGarden and cpuMask. The webGarden attribute takes a Boolean value that indicates whether or not multiple worker processes (one per each affinitized CPU) have to be used. The attribute is set to false by default. The cpuMask attribute stores a DWORD value whose binary representation provides a bit mask for the CPUs that are eligible to run the ASP.NET worker process. The default value is -1 (0xFFFFFF), which means that all available CPUs can be used. The contents of the cpuMask attribute is ignored when the webGarden attribute is false. The cpuMask attribute also sets an upper bound to the number of copies of aspnet_wp.exe that are running.
Web gardening enables multiple worker processes to run at the same time. However, you should note that all processes will have their own copy of application state, in-process session state, ASP.NET cache, static data, and all that is needed to run applications. When the Web garden mode is enabled, the ASP.NET ISAPI launches as many worker processes as there are CPUs, each a full clone of the next (and each affinitized with the corresponding CPU). To balance the workload, incoming requests are partitioned among running processes in a round-robin manner. Worker processes get recycled as in the single processor case. Note that ASP.NET inherits any CPU usage restriction from the operating system and doesn’t include any custom semantics for doing this.
All in all, the Web garden model is not necessarily a big win for all applications. The more stateful applications are, the more they risk to pay in terms of real performance. Working data is stored in blocks of shared memory so that any changes entered by a process are immediately visible to others. However, for the time it takes to service a request, working data is copied in the context of the process. Each worker process, therefore, will handle its own copy of working data, and the more stateful the application, the higher the cost in performance. In this context, careful and savvy application benchmarking is an absolute must.
Changes made to the section of the configuration file are effective only after IIS is restarted. In IIS 6, Web gardening parameters are stored in the IIS metabase; the webGarden and cpuMask attributes are ignored.

Can we handle the error and redirect to some pages using web.config?

Answer :

Yes, we can do this, but to handle errors, we must know the error codes; only then we can take the user to a proper error message page, else it may confuse the user.
CustomErrors Configuration section in web.config file:
The default configuration is:
< mode="RemoteOnly" defaultredirect="Customerror.aspx">
< statuscode="404" redirect="Notfound.aspx">
< /customErrors >
If mode is set to Off, custom error messages will be disabled. Users will receive detailed exception error messages.
If mode is set to On, custom error messages will be enabled.
If mode is set to RemoteOnly, then users will receive custom errors, but users accessing the site locally will receive detailed error messages.
Add an <> tag for each error you want to handle. The error tag will redirect the user to the Notfound.aspx page when the site returns the 404 (Page not found) error.

[Example]
There is a page MainForm.aspx
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
‘Put user code to initialize the page here
Dim str As System.Text.StringBuilder
str.Append(”hi”) ‘ Error Line as str is not instantiated
Response.Write(str.ToString)
End Sub
[Web.Config]
< mode="On" defaultredirect="Error.aspx">
‘ a simple redirect will take the user to Error.aspx [user defined] error file.
< mode="RemoteOnly" defaultredirect="Customerror.aspx">
< statuscode="404" redirect="Notfound.aspx">
< /customErrors >
‘This will take the user to NotFound.aspx defined in IIS.

What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState?

ViewState is the mechanism ASP.NET uses to keep track of server control state values that don’t otherwise post back as part of the HTTP form. ViewState Maintains the UI State of a Page
ViewState is base64-encoded. It is not encrypted but it can be encrypted by setting EnableViewStatMAC=”true” & setting the machineKey validation type to 3DES. If you want to NOT maintain the ViewState, include the directive < %@ Page EnableViewState="false" % > at the top of an .aspx page or add the attribute EnableViewState=”false” to any control.

What is advantage of viewstate and what are benefits?

When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a form with a lot of information and the server comes back with an error. You will have to go back to the form and correct the information. You click the back button, and what happens…….ALL form values are CLEARED, and you will have to start all over again! The site did not maintain your ViewState.With ASP .NET, the form reappears in the browser window together with all form values.This is because ASP .NET maintains your ViewState. The ViewState indicates the status of the page when submitted to the server

What is an HTML “entity”?

An entity is a specific character string that has the effect of causing a formatting program to select and present a particular character or notation.

What’s the safest way to deploy a Windows Forms app?

Web deployment: the user always downloads the latest version of the code, the program runs within security sandbox, properly written app will not require additional security privileges

What class does Icon derive from?

Isn’t it just a Bitmap with a wrapper name around it? No, Icon lives in System.Drawing namespace. It’s not a Bitmap by default, and is treated separately by .NET. However, you can use ToBitmap method to get a valid Bitmap object from a valid Icon object.

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.

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, thisproperty instructs the client application not to save the Cookie on the user’s hard disk when a session ends

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

What is Com Callable wrapper?when it will created?

.NET components are accessed from COM via a COM Callable Wrapper (CCW). This is similar to a RCW, but works in the opposite direction. Again, if the wrapper cannot be automatically generated by the .NET development tools, or if the automatic behaviour is not desirable, a custom CCW can be developed. Also, for COM to ’see’ the .NET component, the .NET component must be registered in the registry.CCWs also manage the object identity and object lifetime of the managed objects they wrap.

What is Runtime Callable wrapper?.when it will created?.

The common language runtime exposes COM objects through a proxy called the runtime callable wrapper (RCW). Although the RCW appears to be an ordinary object to .NET clients, its primary function is to marshal calls between a .NET client and a COM object. This wrapper turns the COM interfaces exposed by the COM component into .NET-compatible interfaces. For oleautomation (attribute indicates that an interface is compatible with Automation) interfaces, the RCW can be generated automatically from a type library. For non-oleautomation interfaces, it may be necessary to develop a custom RCW which manually maps the types exposed by the COM interface to .NET-compatible types.

What is ADO .NET and what is difference between ADO and ADO.NET?

ADO.NET is stateless mechanism. I can treat the ADO.Net as a separate in-memory database where in I can use relationships between the tables and select insert and updates to the database. I can update the actual database as a batch.

since it will call Finalize(), and Finalize() has no guarantees when the memory will be cleaned up, plus, it introduces additional load on the garbage collector.

How does VB.NET/C# achieve polymorphism?
Polymorphism is also achieved through interfaces. Like abstract classes, interfaces also describe the methods that a class needs to implement. The difference between abstract classes and interfaces is that abstract classes always act as a base class of the related classes in the class hierarchy. For example, consider a hierarchy-car and truck classes derived from four-wheeler class; the classes two-wheeler and four-wheeler derived from an abstract class vehicle. So, the class ‘vehicle’ is the base class in the class hierarchy. On the other hand dissimilar classes can implement one interface. For example, there is an interface that compares two objects. This interface can be implemented by the classes like box, person and string, which are unrelated to each other.
C# allows multiple interface inheritance. It means that a class can implement more than one interface. The methods declared in an interface are implicitly abstract. If a class implements an interface, it becomes mandatory for the class to override all the methods declared in the interface, otherwise the derived class would become abstract.
Can you explain what inheritance is and an example of when you might use it? The savingaccount class has two data members-accno that stores account number, and trans that keeps track of the number of transactions. We can create an object of savingaccount class as shown below.
savingaccount s = new savingaccount ( “Amar”, 5600.00f ) ;
From the constructor of savingaccount class we have called the two-argument constructor of the account class using the base keyword and passed the name and balance to this constructor using which the data member’s name and balance are initialised.
We can write our own definition of a method that already exists in a base class. This is called method overriding. We have overridden the deposit( ) and withdraw( ) methods in the savingaccount class so that we can make sure that each account maintains a minimum balance of Rs. 500 and the total number of transactions do not exceed 10. From these methods we have called the base class’s methods to update the balance using the base keyword. We have also overridden the display( ) method to display additional information, i.e. account number.
Working of currentaccount class is more or less similar to that of savingaccount class. Using the derived class’s object, if we call a method that is not overridden in the derived class, the base class method gets executed. Using derived class’s object we can call base class’s methods, but the reverse is not allowed.
Unlike C++, C# does not support multiple inheritance. So, in C# every class has exactly one base class. Now, suppose we declare reference to the base class and store in it the address of instance of derived class as shown below.
account a1 = new savingaccount ( “Amar”, 5600.00f ) ;
account a2 = new currentaccount ( “MyCompany Pvt. Ltd.”, 126000.00f) ;
Such a situation arises when we have to decide at run-time a method of which class in a class hierarchy should get called. Using a1 and a2, suppose we call the method display( ), ideally the method of derived class should get called. But it is the method of base class that gets called. This is because the compiler considers the type of reference (account in this case) and resolves the method call. So, to call the proper method we must make a small change in our program. We must use the virtual keyword while defining the methods in base class as shown below.
public virtual void display( ) { }
We must declare the methods as virtual if they are going to be overridden in derived class. To override a virtual method in derived classes we must use the override keyword as given below.
public override void display( ) { }
Now it is ensured that when we call the methods using upcasted reference, it is the derived class’s method that would get called. Actually, when we declare a virtual method, while calling it, the compiler considers the contents of the reference rather than its type.
If we don’t want to override base class’s virtual method, we can declare it with new modifier in derived class. The new modifier indicates that the method is new to this class and is not an override of a base class method.
What is Jit compilers?.how many are available in clr?
Just-In-Time compiler- it converts the language that you write in .Net into machine language that a computer can understand. there are tqo types of JITs one is memory optimized & other is performace optimized.
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.
Can multiple catch blocks be executed?
It’s a delegate that points to and eventually fires off several methods.
What’s the difference between const and readonly?
You can initialize readonly variables to some runtime values. Let’s say your program uses current date and time as one of the values that won’t change. This way you declare public readonly string DateT = new DateTime().ToString().
What’s the difference between Java and .NET garbage collectors?
Sun left the implementation of a specific garbage collector up to the JRE developer, so their performance varies widely, depending on whose JRE you’re using. Microsoft standardized on their garbage collection.