C# Factory Design PatternUse the factory design pattern. Understand how a factory returns objects for use in a program.
Factory pattern. A factory creates objects. We implement the factory design pattern in a C# program. With this pattern, we develop an abstraction that isolates the logic for determining which type of class to create.
Example. The factory design pattern relies on a type hierarchy. The classes must all implement an interface or derive from a base class. We use an abstract class as the base. The Manager, Clerk and Programmer classes derive from Position.
Get This method takes a value and instantiate a class based on that value. It translates integers to objects with a switch statement.
Abstract Because Manager, Clerk, and Programmer all derive from the same abstract class, the return type Position can be used.
Cast An implicit cast automatically casts the Manager, Clerk and Programmer to Position references.
Main We use the Get method with the values 0, 1, 2, and 3. We show that the appropriate type of class was instantiated for each integer.
Discussion. Imagine you have a system that needs to create objects in many different places. Suppose the system has integers and you want objects for those integers. The factory pattern is ideal for this usage.
Tip You can use the Factory type to handle object creation in a uniform and concise way.
C# program that uses factory pattern
using System; class Program { abstract class Position { public abstract string Title { get; } } class Manager : Position { public override string Title { get { return "Manager"; } } } class Clerk : Position { public override string Title { get { return "Clerk"; } } } class Programmer : Position { public override string Title { get { return "Programmer"; } } } static class Factory { /// <summary> /// Decides which class to instantiate. /// </summary> public static Position Get(int id) { switch (id) { case 0: return new Manager(); case 1: case 2: return new Clerk(); case 3: default: return new Programmer(); } } } static void Main() { for (int i = 0; i <= 3; i++) { var position = Factory.Get(i); Console.WriteLine("Where id = {0}, position = {1} ", i, position.Title); } } }
Where id = 0, position = Manager Where id = 1, position = Clerk Where id = 2, position = Clerk Where id = 3, position = Programmer
Summary. We looked the factory design pattern, which is used to instantiate objects based on another data type such as integers. Factories can be used to reduce code bloat and also make it easier to modify which objects need to be created.
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