Hello Friends. I was just wondering if anyone has a lot of experience working with Lists of type Interface and could share some of the interesting things you can use them for. Also, is there a way to sum a column in a List of Interface type? Thanks !!!!

Can you provide us a more concrete example of what you're looking for here? A list of interfaces? public interface IShape {} public class Circle: IShape {} public class Rectangle: IShape {} public class Triangle: IShape {} var shapes = new List<IShape>(); shapes.Add(new Circle()); shapes.Add(new Triangle()); shapes.Add(new Rectangle()); To sum a set of anything use the LINQ method Sum . var numbers = new [] { 10, 20, 30, 40 }; var sum = numbers.Sum(); It works with any type (interface or otherwise) provided you refer to the property that contains the value you want to sum. public interface IMyInterface { int SomeValue { get; set; } } var items = new List<IMyInterface>(); ... var sum = items.Sum(x => x.SomeValue);

List of Type Interface - Microsoft Q&A

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Michael Taylor 54,811 Reputation points

2022-12-13T17:33:15.807+00:00
Can you provide us a more concrete example of what you're looking for here?

A list of interfaces?

public interface IShape {} public class Circle: IShape {} public class Rectangle: IShape {} public class Triangle: IShape {} var shapes = new List<IShape>(); shapes.Add(new Circle()); shapes.Add(new Triangle()); shapes.Add(new Rectangle());

To sum a set of anything use the LINQ method Sum.

var numbers = new [] { 10, 20, 30, 40 }; var sum = numbers.Sum();

It works with any type (interface or otherwise) provided you refer to the property that contains the value you want to sum.

public interface IMyInterface { int SomeValue { get; set; } } var items = new List<IMyInterface>(); ... var sum = items.Sum(x => x.SomeValue);
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Ronald Rex 181 Reputation points

2022-12-13T17:51:48.167+00:00

Thanks for your help. I was just referring to maybe someone might be able to tell me how you might apply a List of Interfaces in a real world application. I understand how they are used in theory and I have used them before in an application. But I want to get really good with using them and applying them in different real world use cases.

Michael Taylor 54,811 Reputation points

2022-12-13T19:02:23.317+00:00

Interfaces are used all the time to decouple implementation from usage. If you follow that design throughout your code then eventually you're going to need to have a set of items represented by interfaces and that is when you might use a list of them. One real world example might be validators in an application. Your business rules may be more complex than what the existing validation infrastructure supports so you might switch to a validation library or build your own. Suppose you build your own.

public interface IValidator<T> { bool IsValid ( T value, List<ValidationResult> results ); }

You might implement different validators for a business object Employee. Things like CanNotReportToSelf, RequiresSupervisor and MustBeFullTime. You might store all these in a list so you can pass all the validators to other areas of the code that needs to validate an Employee.

var employeeValidators = new List<IValidator<Employee>>() { new CanNotReportToSelfValidator(), new RequiresSupervisorValidator(), new MustBeFullTimeValidator() }; bool IsEmployeeValid ( Employee employee, list<IValidator<Employee>> validators ) { ... }

Ronald Rex 181 Reputation points

2022-12-13T19:09:23.097+00:00

Thanks for being very helpful !!!!
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