Question

How we can filter the object in List<> in C#?

Answer 1

Let’s say we have a List<string> and you want only the items where the length of the string is greater than 5.

The code below will return a List<string> with the results:

List<string> myList = new List<string>();
myList.Add("hello");
myList.Add("world!");
myList.Add("one");
myList.Add("large!!");
List<string> resultList = myList.FindAll(delegate(string s) { return s.Length > 5; });

resultList will containt ‘world!’ and ‘large!!’.
This example uses an anonymous method. It can also be written as:

List<string> myList = new List<string>();
// ..
List<string> resultList = myList.FindAll(OnlyLargerThanFive);

//..

private static bool OnlyLargerThanFive(string s)
{
  return s.Length > 5;
}

The delegate above, OnlyLargerThanFive, is also called a Predicate.