Question

Can you explain to me:

• What is a Predicate Delegate?
• Where should we use predicates?
• Any best practices when using predicates?

Descriptive source code will be appreciated.

Answer 1

A predicate is a function that returns true or false. A predicate delegate is a reference to a predicate.

So basically a predicate delegate is a reference to a function that returns true or false. Predicates are very useful for filtering a list of values – here is an example.

using System; using System.Collections.Generic;  class Program {     static void Main()     {         List<int> list = new List<int> { 1, 2, 3 };          Predicate<int> predicate = new Predicate<int>(greaterThanTwo);          List<int> newList = list.FindAll(predicate);     }      static bool greaterThanTwo(int arg)     {         return arg > 2;     } } 

Now if you are using C# 3 you can use a lambda to represent the predicate in a cleaner fashion:

using System; using System.Collections.Generic;  class Program {     static void Main()     {         List<int> list = new List<int> { 1, 2, 3 };          List<int> newList = list.FindAll(i => i > 2);     } }