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SOLID & IOC PRINCIPLESThe basic principles of OOP design

What is SOLID?The first five principles of OOP design.A set of rules on how to build an awesome application that is flexible and easy to use, understand and maintain.

SINGLE RESPONSIBILITY PRINCIPLEA class should have only one reason to change

Robert C. Martin

SINGLE RESPONSIBILITY PRINCIPLE// Data access class is only responsible for data base related operations

class DataAccess{ public static void InsertData() { Console.WriteLine("Data inserted into database successfully"); }}

// Data access class is only responsible for data base related operations

class DataAccess{ public static void InsertData() { Logger.WriteLog("Data inserted into database successfully"); }}

// Logger class is only responsible for logging related operations class Logger{ public static void WriteLog(string messsage) { Console.WriteLine("Logged Time:" + DateTime.Now + messsage); }}

OPEN/CLOSED PRINCIPLEObjects or entities should be open for extension, but closed for modification

Bertrand Meyer

OPEN/CLOSED PRINCIPLE// Here DataProvider is open for extension (extends to Sql, Oracle, Oledb Providers and so on..) and closed for manipulation

abstract class DataProvider{ public abstract int OpenConnection(); public abstract int CloseConnection(); public abstract int ExecuteCommand();}

class SqlDataProvider : DataProvider{ public override int OpenConnection() { Console.WriteLine("\nSql Connection opened"); return 1; } public override int CloseConnection() { Console.WriteLine("Sql Connection closed"); return 1; } public override int ExecuteCommand() { Console.WriteLine("Sql Command Executed"); return 1; }}

OPEN/CLOSED PRINCIPLEclass OracleDataProvider : DataProvider{ public override int OpenConnection() { Console.WriteLine("Oracle Connection opened"); return 1; } public override int CloseConnection() { Console.WriteLine("Oracle Connection closed"); return 1; } public override int ExecuteCommand() { Console.WriteLine("Oracle Command Executed"); return 1; }}

class OpenClosePrincipleDemo{ public static void OSPDemo() { Console.WriteLine("Open Close Principle");

DataProvider DataProviderObject = new SqlDataProvider();

DataProviderObject.OpenConnection(); DataProviderObject.ExecuteCommand(); DataProviderObject.CloseConnection();

DataProviderObject = new OracleDataProvider(); DataProviderObject.OpenConnection(); DataProviderObject.ExecuteCommand(); DataProviderObject.CloseConnection(); }}

LISKOV SUBSTITUTION PRINCIPLELet f(x) be a property of objects X of type T. Then f(y) should be true for objects Y of type S where S is a subtype of T

Barbara Liskov

LISKOV SUBSTITUTION PRINCIPLE// While implementing derived classes, one needs to ensure that, derived classes just extend the functionality of base classes without replacing the functionality of base classes.

class Rectangle{ protected int mWidth = 0; protected int mHeight = 0;

public virtual void SetWidth(int width) { mWidth = width; } public virtual void SetHeight(int height) { mHeight = height; } public virtual int GetArea() { return mWidth * mHeight; }}

// While implementing derived class if one replaces the functionality of base class then, // it might results into undesired side effects when such derived classes are used in existing program modules. class Square : Rectangle{ // This class modifies the base class functionality instead of extending the base class functionality. Now below methods implementation will impact base class functionality. public override void SetWidth(int width) { mWidth = width; mHeight = width; }

public override void SetHeight(int height) { mWidth = height; mHeight = height; }}

INTERFACE SEGREGATION PRINCIPLEMany client-specific interfaces are better than one general-purpose interface

Robert C. Martin

INTERFACE SEGREGATION PRINCIPLEStates that no client should be forced to depend on methods it does not use. Thus having multiple grained interfaces is better that one

INTERFACE SEGREGATION PRINCIPLE// Only common generic methods exists for all derived classes. interface IDataProvider{ int OpenConnection(); int CloseConnection();}

// Implement methods specific to the respective derived classes interface ISqlDataProvider : IDataProvider{ int ExecuteSqlCommand();}

// Implement methods specific to the respective derived classes interface IOracleDataProvider : IDataProvider{ int ExecuteOracleCommand();}

// Should not force SqlDataProvider client to implement ExecuteOracleCommand, as it wont required that method to be implemented. class SqlDataClient : ISqlDataProvider{ public int OpenConnection() { Console.WriteLine("Sql Connection opened"); return 1; } public int CloseConnection() { Console.WriteLine("Sql Connection closed"); return 1; }

public int ExecuteSqlCommand() { Console.WriteLine("Sql Server specific

Command Executed successfully"); return 1; }}

INTERFACE SEGREGATION PRINCIPLEclass OracleDataClient : IOracleDataProvider{ public int OpenConnection() { Console.WriteLine("Oracle Connection opened"); return 1; } public int CloseConnection() { Console.WriteLine("Oracle Connection closed"); return 1; } public int ExecuteOracleCommand() { Console.WriteLine("Oracle specific Command Executed successfully"); return 1; }}

class InterfaceSegregationPrincipleDemo{ public static void ISPDemo() { Console.WriteLine("Interface Inversion Principle Demo ");

ISqlDataProvider SqlDataProviderObject = new SqlDataClient();

SqlDataProviderObject.OpenConnection(); SqlDataProviderObject.ExecuteSqlCommand(); SqlDataProviderObject.CloseConnection();

IOracleDataProvider OracleDataProviderObject

= new OracleDataClient(); OracleDataProviderObject.OpenConnection(); OracleDataProviderObject.ExecuteOracleCommand(); OracleDataProviderObject.CloseConnection(); }}

DEPENDENCY INVERSION PRINCIPLEOne should depend upon abstractions, not on concretions

Robert C. Martin

DEPENDENCY INVERSION PRINCIPLEA. High-level modules should not depend

on low-level modules. Both should depend on abstractions.

B. Abstractions should not depend on details. Details should depend on abstractions.

DEPENDENCY INVERSION PRINCIPLEpublic interface ITransferSource{ long AccountNumber { get; set; } decimal Balance { get; set; } void RemoveFunds(decimal value);}

public interface ITransferDestination{ long AccountNumber { get; set; } decimal Balance { get; set; } void AddFunds(decimal value);}

public class BOABankAccount : ITransferSource, ITransferDestination

{ public long AccountNumber { get; set; } public decimal Balance { get; set; }

public void AddFunds(decimal value) { Balance += value; } public void RemoveFunds(decimal value) { Balance -= value; }}

DEPENDENCY INVERSION PRINCIPLEpublic class TransferAmounts{ public decimal Amount { get; set; }

public void Transfer( ITransferSource TransferSource, ITransferDestination TransferDestination) { TransferSource.RemoveFunds(Amount); TransferDestination.AddFunds(Amount); }}

public class BOABankAccount : ITransferSource, ITransferDestination{ public long AccountNumber { get; set; } public decimal Balance { get; set; }

public void AddFunds(decimal value) { Balance += value; } public void RemoveFunds(decimal value) { Balance -= value; }}

INVERSION OF CONTROL PRINCIPLEDescribes a design in which custom-written portions of a computer program receive the flow of control from a generic, reusable library

What For?• To decouple the execution of a task from

implementation.• To focus a module on the task it is

designed for.• To free modules from assumptions about

how other systems do what they do and instead rely on contracts.

• To prevent side effects when replacing a module.

Types of IoCDependency

Inversion

Inversion of Control

Delegates Events Service Locator

Dependency Injection

Constructor Injection

Property Injection

Method Injection

DEPENDENCY INJECTION PATTERNA software design pattern that implements inversion of control for resolving dependencies through:

• Constructor Injection• Method Injection• Property Injection

DEPENDENCY INJECTION PATTERNProblem Solution

SERVICE LOCATOR PATTERNA design pattern used in software development to encapsulate the processes involved in obtaining a service with a strong abstraction layer.

SERVICE LOCATOR PATTERNProblem Solution

IOC CONTAINERSWhat for?• Is responsible for creating

objects• Is responsible for

dependency injection• Manages lifetime of those

objects• Removes dependencies

from your code

Concrete Implementations• Microsoft Unity• Castle Windsor• Ninject• Spring.NET• Light Inject• Simple Injector

SOFTWARE TESTABILITYIf your code isn't testable, then you have a design problem

Common Sense

WHAT MAKES YOUR CODE TESTABLE ?SRP

Since type is doing only one job, you can clearly understand what should be tested.

LSP

Since types used can be replaced with subtypes, mocks and stubs can be used instead of real types.

ISP

Since there are more granular client-specific interfaces, you know exactly what to mock.

LET’S REVIEW SOME CONCEPTSReusableHigher-level components can be reused if lower-lever components change with time to meet the requirements.

ExtensibleSoftware is easily extended with new components and features because design is based on abstractions.

ReplaceableLower-level components can be replaced to meet new requirements without modifying existing code.

Loosely CoupledAllows components to perform on their own with as little knowledge as possible about other components.

CohesiveBuild you software easily with different components as building blocks.

TestableIt is easy to understand what and how to test in each component because components are loosely-coupled.

Additional Linkshttp://www.csharpstar.com/solid-design-principles-c/http://www.codeproject.com/Articles/703634/SOLID-architecture-principles-using-simple-Csharp#Understanding%E2%80%9CS%E2%80%9D-SRP(Singleresponsibilityprinciple). https://code.msdn.microsoft.com/windowsapps/OOPS-Principles-SOLID-7a4e69bfhttp://programmers.stackexchange.com/questions/202571/solid-principles-and-code-structure

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