Dictionary(Of TKey, TValue).ContainsKey Method (TKey)
Determines whether the Dictionary(Of TKey, TValue) contains the specified key.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- key
-
Type:
TKey
The key to locate in the Dictionary(Of TKey, TValue).
Return Value
Type: System.Booleantrue if the Dictionary(Of TKey, TValue) contains an element with the specified key; otherwise, false.
| Exception | Condition |
|---|---|
| ArgumentNullException | key is null. |
This method approaches an O(1) operation.
The following code example shows how to use the ContainsKey method to test whether a key exists prior to calling the Add method. It also shows how to use the TryGetValue method to retrieve values, which is an efficient way to retrieve values when a program frequently tries keys that are not in the dictionary. Finally, it shows the least efficient way to test whether keys exist, by using the Item property (the indexer in C#).
This code example is part of a larger example provided for the Dictionary(Of TKey, TValue) class (openWith is the name of the Dictionary used in this example).
' ContainsKey can be used to test keys before inserting ' them. If Not openWith.ContainsKey("ht") Then openWith.Add("ht", "hypertrm.exe") Console.WriteLine("Value added for key = ""ht"": {0}", _ openWith("ht")) End If
' When a program often has to try keys that turn out not to ' be in the dictionary, TryGetValue can be a more efficient ' way to retrieve values. Dim value As String = "" If openWith.TryGetValue("tif", value) Then Console.WriteLine("For key = ""tif"", value = {0}.", value) Else Console.WriteLine("Key = ""tif"" is not found.") End If
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1