Collection<T>.Contains Method
Determines whether an element is in the Collection<T>.
Namespace: System.Collections.ObjectModel
Assembly: mscorlib (in mscorlib.dll)
Parameters
- item
- Type: T
The object to locate in the Collection<T>. The value can be null for reference types.
Implements
ICollection<T>.Contains(T)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.
The following code example demonstrates many of the properties and methods of Collection<T>. The code example creates a collection of strings, uses the Add method to add several strings, displays the Count, and lists the strings. The example uses the IndexOf method to find the index of a string and the Contains method to determine whether a string is in the collection. The example inserts a string using the Insert method and retrieves and sets strings using the default Item property (the indexer in C#). The example removes strings by string identity using the Remove method and by index using the RemoveAt method. Finally, the Clear method is used to clear all strings from the collection.
using System; using System.Collections.Generic; using System.Collections.ObjectModel; public class Example { public static void Demo(System.Windows.Controls.TextBlock outputBlock) { Collection<string> dinosaurs = new Collection<string>(); dinosaurs.Add("Psitticosaurus"); dinosaurs.Add("Caudipteryx"); dinosaurs.Add("Compsognathus"); dinosaurs.Add("Muttaburrasaurus"); outputBlock.Text += String.Format("{0} dinosaurs:", dinosaurs.Count) + "\n"; Display(outputBlock, dinosaurs); outputBlock.Text += String.Format("\nIndexOf(\"Muttaburrasaurus\"): {0}", dinosaurs.IndexOf("Muttaburrasaurus")) + "\n"; outputBlock.Text += String.Format("\nContains(\"Caudipteryx\"): {0}", dinosaurs.Contains("Caudipteryx")) + "\n"; outputBlock.Text += String.Format("\nInsert(2, \"Nanotyrannus\")") + "\n"; dinosaurs.Insert(2, "Nanotyrannus"); Display(outputBlock, dinosaurs); outputBlock.Text += String.Format("\ndinosaurs[2]: {0}", dinosaurs[2]) + "\n"; outputBlock.Text += "\ndinosaurs[2] = \"Microraptor\"" + "\n"; dinosaurs[2] = "Microraptor"; Display(outputBlock, dinosaurs); outputBlock.Text += "\nRemove(\"Microraptor\")" + "\n"; dinosaurs.Remove("Microraptor"); Display(outputBlock, dinosaurs); outputBlock.Text += "\nRemoveAt(0)" + "\n"; dinosaurs.RemoveAt(0); Display(outputBlock, dinosaurs); outputBlock.Text += "\ndinosaurs.Clear()" + "\n"; dinosaurs.Clear(); outputBlock.Text += String.Format("Count: {0}", dinosaurs.Count) + "\n"; } private static void Display(System.Windows.Controls.TextBlock outputBlock, Collection<string> cs) { outputBlock.Text += "\n"; foreach (string item in cs) { outputBlock.Text += item + "\n"; } } } /* This code example produces the following output: 4 dinosaurs: Psitticosaurus Caudipteryx Compsognathus Muttaburrasaurus IndexOf("Muttaburrasaurus"): 3 Contains("Caudipteryx"): True Insert(2, "Nanotyrannus") Psitticosaurus Caudipteryx Nanotyrannus Compsognathus Muttaburrasaurus dinosaurs[2]: Nanotyrannus dinosaurs[2] = "Microraptor" Psitticosaurus Caudipteryx Microraptor Compsognathus Muttaburrasaurus Remove("Microraptor") Psitticosaurus Caudipteryx Compsognathus Muttaburrasaurus RemoveAt(0) Caudipteryx Compsognathus Muttaburrasaurus dinosaurs.Clear() Count: 0 */
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