12. Advantages of migrating to VB.NET ?
Visual Basic .NET has many new and improved language features — such as inheritance, interfaces, and overloading that make it a powerful object-oriented programming language. As a Visual Basic developer, you can now create multithreaded, scalable applications using explicit multithreading. Other new language features in Visual Basic .NET include structured exception handling, custom attributes, and common language specification (CLS) compliance.
The CLS is a set of rules that standardizes such things as data types and how objects are exposed and interoperate. Visual Basic .NET adds several features that take advantage of the CLS. Any CLS-compliant language can use the classes, objects, and components you create in Visual Basic .NET. And you, as a Visual Basic user, can access classes, components, and objects from other CLS-compliant programming languages without worrying about language-specific differences such as data types. CLS features used by Visual Basic .NET programs include assemblies, namespaces, and attributes. These are the new features to be stated briefly:
Inheritance
Visual Basic .NET supports inheritance by allowing you to define classes that serve as the basis for derived classes. Derived classes inherit and can extend the properties and methods of the base class. They can also override inherited methods with new implementations. All classes created with Visual Basic .NET are inheritable by default. Because the forms you design are really classes, you can use inheritance to define new forms based on existing ones.
Exception Handling
Visual Basic .NET supports structured exception handling, using an enhanced version of the Try…Catch…Finally syntax supported by other languages such as C++.
Structured exception handling combines a modern control structure (similar to Select Case or While) with exceptions, protected blocks of code, and filters. Structured exception handling makes it easy to create and maintain programs with robust, comprehensive error handlers.
Overloading
Overloading is the ability to define properties, methods, or procedures that have the same name but use different data types. Overloaded procedures allow you to provide as many implementations as necessary to handle different kinds of data, while giving the appearance of a single, versatile procedure. Overriding Properties and Methods The Overrides keyword allows derived objects to override characteristics inherited from parent objects. Overridden members have the same arguments as the members inherited from the base class, but different implementations. A member’s new implementation can call the original implementation in the parent class by preceding the member name with MyBase.
Constructors and Destructors
Constructors are procedures that control initialization of new instances of a class. Conversely, destructors are methods that free system resources when a class leaves scope or is set to Nothing. Visual Basic .NET supports constructors and destructors using the Sub New and Sub Finalize procedures.
Data Types
Visual Basic .NET introduces three new data types. The Char data type is an unsigned 16-bit quantity used to store Unicode characters. It is equivalent to the .NET Framework System. Char data type. The Short data type, a signed 16-bit integer, was named Integer in earlier versions of Visual Basic. The Decimal data type is a 96-bit signed integer scaled by a variable power of 10. In earlier versions of Visual Basic, it was available only within a Variant.
Interfaces
Interfaces describe the properties and methods of classes, but unlike classes, do not provide implementations. The Interface statement allows you to declare interfaces, while the Implements statement lets you write code that puts the items described in the interface into practice.
Delegates
Delegates objects that can call the methods of objects on your behalf are sometimes described as type-safe, object-oriented function pointers. You can use delegates to let procedures specify an event handler method that runs when an event occurs. You can also use delegates with multithreaded applications. For details, see Delegates and the AddressOf Operator.
Shared Members
Shared members are properties, procedures, and fields that are shared by all instances of a class. Shared data members are useful when multiple objects need to use information that is common to all. Shared class methods can be used without first creating an object from a class.
References
References allow you to use objects defined in other assemblies. In Visual Basic .NET, references point to assemblies instead of type libraries. For details, see References and the Imports Statement. Namespaces Namespaces prevent naming conflicts by organizing classes, interfaces, and methods into hierarchies.
Assemblies
Assemblies replace and extend the capabilities of type libraries by, describing all the required files for a particular component or application. An assembly can contain one or more namespaces.
Attributes
Attributes enable you to provide additional information about program elements. For example, you can use an attribute to specify which methods in a class should be exposed when the class is used as a XML Web service. Multithreading
Visual Basic .NET allows you to write applications that can perform multiple tasks independently. A task that has the potential of holding up other tasks can execute on a separate thread, a process known as multithreading. By causing complicated tasks to run on threads that are separate from your user interface, multithreading makes your applications more responsive to user input.
13. Advantages of VB.NET
First of all, VB.NET provides managed code execution that runs under the Common Language Runtime (CLR), resulting in robust, stable and secure applications. All features of the .NET framework are readily available in VB.NET.
VB.NET is totally object oriented. This is a major addition that VB6 and other earlier releases didn’t have.
The .NET framework comes with ADO.NET, which follows the disconnected paradigm, i.e. once the required records are fetched the connection no longer exists. It also retrieves the records that are expected to be accessed in the immediate future. This enhances Scalability of the application to a great extent.
VB.NET uses XML to transfer data between the various layers in the DNA Architecture i.e. data are passed as simple text strings.
Error handling has changed in VB.NET. A new Try-Catch-Finally block has been introduced to handle errors and exceptions as a unit, allowing appropriate action to be taken at the place the error occurred thus discouraging the use of ON ERROR GOTO statement. This again credits to the maintainability of the code.
Another great feature added to VB.NET is free threading against the VB single-threaded apartment feature. In many situations developers need spawning of a new thread to run as a background process and increase the usability of the application. VB.NET allows developers to spawn threads wherever they feel like, hence giving freedom and better control on the application.
Security has become more robust in VB.NET. In addition to the role-based security in VB6, VB.NET comes with a new security model, Code Access security. This security controls on what the code can access. For example you can set the security to a component such that the component cannot access the database. This type of security is important because it allows building components that can be trusted to various degrees.
The CLR takes care of garbage collection i.e. the CLR releases resources as soon as an object is no more in use. This relieves the developer from thinking of ways to manage memory. CLR does this for them.
14. Using ActiveX Control in .Net
ActiveX control is a special type of COM component that supports a User Interface. Using ActiveX Control in your .Net Project is even easier than using COM component. They are bundled usually in .ocx files. Again a proxy assembly is made by .Net utility AxImp.exe (which we will see shortly) which your application (or client) uses as if it is a .Net control or assembly.
Making Proxy Assembly For ActiveX Control: First, a proxy assembly is made using AxImp.exe (acronym for ActiveX Import) by writing following command on Command Prompt:
C:>AxImp C:MyProjectsMyControl.ocx
This command will make two dlls, e.g., in case of above command
MyControl.dll
AxMyControl.dll
The first file MyControl.dll is a .Net assembly proxy, which allows you to reference the ActiveX as if it were non-graphical object.
The second file AxMyControl.dll is the Windows Control, which allows u to use the graphical aspects of activex control and use it in the Windows Form Project.
Adding Reference of ActiveX Proxy Assembly in your Project Settings: To add a reference of ActiveX Proxy Assembly in our Project, do this:
o Select ProjectàAdd Reference (Select Add Reference from Project Menu).
o This will show you a dialog box, select .Net tab from the top of window.
o Click Browse button on the top right of window.
o Select the dll file for your ActiveX Proxy Assembly (which is MyControl.dll) and click OK o Your selected component is now shown in the ‘Selected Component’ List Box. Click OK again Some More On Using COM or ActiveX in .Net
.Net only provides wrapper class or proxy assembly (Runtime Callable Wrapper or RCW) for COM or activeX control. In the background, it is actually delegating the tasks to the original COM, so it does not convert your COM/activeX but just imports them.
A good thing about .Net is that when it imports a component, it also imports the components that are publically referenced by that component. So, if your component, say MyDataAcsess.dll references ADODB.dll then .Net will automatically import that COM component too!
The Visual Studio.NET does surprise you in a great deal when u see that it is applying its intellisense (showing methods, classes, interfaces, properties when placing dot) even on your imported COM components!!!! Isn’t it a magic or what?
When accessing thru RCW, .Net client has no knowledge that it is using COM component, it is presented just as another C# assembly.
U can also import COM component thru command prompt (for reference see Professional C# by Wrox) U can also use your .Net components in COM, i.e., export your .net components (for reference see Professional C# by Wrox) -6
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