Hello everyone,

a new day, a new learning experience. Today I work on the “Classes” chapter of my exam-preperation and will share the most interesting parts with you.

Inheritance

• Inheritance and Interfaces provide a way to improve a systems consistency
• via Inheritance you can create new classes from existing once
• With inheritance there comes the possibility to use derived classes interchangeably. That is calles polymorphism. You can for example pass an object of type specialobject (Inheriting of object) to a method which excepts an object.

Interfaces

• Interfaces are contract defining required members the new class must provide. For example the IComparable Interface defines a member method called CompareTo. Every class that implements IComparable must implement this Method.
• Commonly used Interfaces: IComparable, IFormattable, IEuatable, ICloneable, IConvertible, IDisposable
• Example Interface:
  
public interface IMyInterface
{
bool DoSomething();
string Message {get; set; }
int MyNumber {get;set;}
}

• “Extract Interface” is a build in Refactoring-Method of Visual Studio

Partial Classes

• A Class-Definintion can be split into different .cs files. This must be declared by using “partial” keyword in class definition (ex. public partial class}

Generics

• With Generics you can define a type and leav some details unspecified. You dont have to specify the type of certain parameters or members, instead you can define them, when using the new type
• Generics will be a bigger part of the exam
• In System.Collections.Generic you can find some Generics like Dictionary, Queue, SortedDictionary or SortedList.
• Advantages: Reduced run-time-errors (More typesafe) and improve performance (avoids boxing and unboxing)
• Example of Definition:
  
  class MyGeneric
  {
  public T t;
  public U u;

  public MyGeneric(T _t, U _u)
{
t = _t;
u = _u;
}
}


• Important: Code needs to compile for every possible usage !
• Comsuming Example:
  
var test = new MyGeneric("hallo",12);

• Constraints for the Types used (T and U in the example above) can be defined.
  
class MyGeneric where T : IDisposable

• You can use Interfaces, Baseclasses,Constructors and Reference of value types as constraints

Events

• object (Event senders) can trigger events when an action takes place (User clicks button, method completed etc.)
• Event Receivers can handle these events when they occure
• A Delegate is a reference (pointer) to a method that itself has no code.
• The Delegates signature must match the signature of the handling method
• Things to do, to create a custom event:
  1. Create Delegate: public delegate void MyEventHandler(object sender, EventArgs e);
  2. Create event: public event MyEventHandler MyEvent;
  3. Fire Event
if (MyEvent != null)
{
// Invoke Delegate
MyEvent(this, new EventArgs());
}

  4. You can create your own EventArgs. Just create a new Class, that inherits from EventArgs.

Attributes

• Attributes describe Methods or Properties. You can get this information by reflection.
• Commonly used attributes for: Security Privileges, capability (ex.Serialization), description (title, copyright…)
• Attribute Types derive from System.Attribute
• Example – AssemblyAttributes in AssemblyInfo.cs : [assembly: AssemblyTitle("title")]
• Declaring capabilities:
  
[Serializable]
class MyClass
{
}

  Without this Attribute, a class is not serializable.
• Declaring Security Requirements
  
[assembly:FileIOPermissionAttribute(SecurityAction.RequestMinimum, Read=@"C:\settings.ini")]
namespace MyNamespace
{
...
}


Type Forwarding

• Move a type from one assembly to another without needing recompile
• TypeForwardedTo – Attribute
• Example:
  
using System.Runtime.CompilerServices;
[assembly:TypeForwardedTo(typeof(TargetLib.MyType))]

• Works only for components referenced by existing applications
• To use Forwarding, do the following:
  1. Add TypeForwardedTo attribute to source assembly
  2. Cut Typedefinition from source and paste to destination
  3. Re-Compile both.

What have I learned ?

I havent used Attributes very often, so it was a good brush-up, and the Type-Forwarding Part was new for me, so I learned something today – Hurray ! )

Next Topic will be “Type Conversion” .. .stay tuned !

Verwandte Artikel

• MCTS Examen 70-536 - Ein Vorwort
• MCTS Examen 70-536 - Value Types
• MCTS Examen 70-536 - Common Reference Types

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