SortedDictionary<TKey,TValue>.Item[TKey] Property

Definition

Namespace:

System.Collections.Generic

Assembly:

System.Collections.dll

Source:

SortedDictionary.cs

Gets or sets the value associated with the specified key.

public:
 property TValue default[TKey] { TValue get(TKey key); void set(TKey key, TValue value); };

public TValue this[TKey key] { get; set; }

member this.Item('Key) : 'Value with get, set

Default Public Property Item(key As TKey) As TValue

Parameters

key

TKey

The key of the value to get or set.

Property Value

TValue

The value associated with the specified key. If the specified key is not found, a get operation throws a KeyNotFoundException, and a set operation creates a new element with the specified key.

Implements

Item[TKey]

Exceptions

ArgumentNullException

key is null.

KeyNotFoundException

The property is retrieved and key does not exist in the collection.

Examples

The following code example uses the Item[] property (the indexer in C#) to retrieve values, demonstrating that a KeyNotFoundException is thrown when a requested key is not present, and showing that the value associated with a key can be replaced.

The example also shows how to use the TryGetValue method as a more efficient way to retrieve values if a program often must try key values that are not in the dictionary.

This code example is part of a larger example provided for the SortedDictionary<TKey,TValue> class.

// The Item property is another name for the indexer, so you
// can omit its name when accessing elements.
Console.WriteLine("For key = \"rtf\", value = {0}.",
    openWith["rtf"]);

// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] = "winword.exe";
Console.WriteLine("For key = \"rtf\", value = {0}.",
    openWith["rtf"]);

// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";

' The Item property is the default property, so you 
' can omit its name when accessing elements. 
Console.WriteLine("For key = ""rtf"", value = {0}.", _
    openWith("rtf"))

' The default Item property can be used to change the value
' associated with a key.
openWith("rtf") = "winword.exe"
Console.WriteLine("For key = ""rtf"", value = {0}.", _
    openWith("rtf"))

' If a key does not exist, setting the default Item property
' for that key adds a new key/value pair.
openWith("doc") = "winword.exe"

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
    Console.WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException)
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' The default Item property throws an exception if the requested
' key is not in the dictionary.
Try
    Console.WriteLine("For key = ""tif"", value = {0}.", _
        openWith("tif"))
Catch 
    Console.WriteLine("Key = ""tif"" is not found.")
End Try

// 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", out value))
{
    Console.WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' 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

Remarks

This property provides the ability to access a specific element in the collection by using the following C# syntax: myCollection[key] (myCollection(key) in Visual Basic).

You can also use the Item[] property to add new elements by setting the value of a key that does not exist in the SortedDictionary<TKey,TValue>; for example, myCollection["myNonexistentKey"] = myValue. However, if the specified key already exists in the SortedDictionary<TKey,TValue>, setting the Item[] property overwrites the old value. In contrast, the Add method does not modify existing elements.

A key cannot be null, but a value can be, if the value type TValue is a reference type.

The C# language uses the this keyword to define the indexers instead of implementing the Item[] property. Visual Basic implements Item[] as a default property, which provides the same indexing functionality.

Getting the value of this property is an O(log n) operation; setting the property is also an O(log n) operation.

See also

• Add(TKey, TValue)