.NET Framework 4.6 and 4.5
If the Collection<T> object is created using the default constructor, this method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list. If type T does not implement the IEquatable<T> interface, the Equals method is used.
If the Collection object is created by passing an IList<T> object to the constructor, the Contains method will be determined by the IEqualityComparer<T> interface used by that IList<T> object.
This method performs a linear search; therefore, the average execution time is proportional to Count. That is, this method is an O(n) operation, where n is Count.
Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0
.NET Framework Client Profile
Supported in: 4, 3.5 SP1
Supported in: 3.0, 2.0, 1.0
.NET for Windows Phone apps
Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8
Portable Class Library
Supported in: Portable Class Library