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

Definition

Namespace:

System.Collections.Generic

Assembly:

System.Collections.dll

Source:

SortedList.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 whose 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 using 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 sorted list.

This code example is part of a larger example provided for the SortedList<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 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 Item property is another name for the indexer, so you
// can omit its name when accessing elements.
printfn $"""For key = "rtf", value = {openWith["rtf"]}."""

// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] <- "winword.exe"
printfn $"""For key = "rtf", value = {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 indexer throws an exception if the requested key is
// not in the list.
try
{
    Console::WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException^)
{
    Console::WriteLine("Key = \"tif\" is not found.");
}

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

// The indexer throws an exception if the requested key is
// not in the list.
try
    printfn $"""For key = "tif", value = {openWith["tif"]}."""
with 
    | :? KeyNotFoundException ->
        printfn "Key = \"tif\" is not found."

// When a program often has to try keys that turn out not to
// be in the list, 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.");
}

// When a program often has to try keys that turn out not to
// be in the list, 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 list, 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

// When a program often has to try keys that turn out not to
// be in the list, TryGetValue can be a more efficient
// way to retrieve values.
match openWith.TryGetValue("tif") with
| true, value ->
    printfn "For key = \"tif\", value = {value}."
| false, _ ->
    printfn "Key = \"tif\" is not found."

Remarks

This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[key].

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

If the key is not found when a value is being retrieved, KeyNotFoundException is thrown. If the key is not found when a value is being set, the key and value are added.

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

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.

Retrieving the value of this property is an O(log n) operation, where n is Count. Setting the property is an O(log n) operation if the key is already in the SortedList<TKey,TValue>. If the key is not in the list, setting the property is an O(n) operation for unsorted data, or O(log n) if the new element is added at the end of the list. If insertion causes a resize, the operation is O(n).

See also

• Add(TKey, TValue)