Dictionary<TKey, TValue>::ContainsKey Method (TKey)
Determines whether the Dictionary<TKey, TValue> contains the specified key.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- key
-
Type:
TKey
The key to locate in the Dictionary<TKey, TValue>.
Return Value
Type: System::Booleantrue if the Dictionary<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<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 (!openWith->ContainsKey("ht")) { openWith->Add("ht", "hypertrm.exe"); Console::WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]); }
// 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. String^ value = ""; if (openWith->TryGetValue("tif", value)) { Console::WriteLine("For key = \"tif\", value = {0}.", value); } else { Console::WriteLine("Key = \"tif\" is not found."); }
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