注意:此类在 .NET Framework 2.0 版中是新增的。
表示按键排序的键/值对的集合。
命名空间:System.Collections.Generic
程序集:System(在 system.dll 中)
<SerializableAttribute> _
Public Class SortedDictionary(Of TKey, TValue)
Implements IDictionary(Of TKey, TValue), ICollection(Of KeyValuePair(Of TKey, TValue)), _
IEnumerable(Of KeyValuePair(Of TKey, TValue)), IDictionary, ICollection, _
IEnumerable
Dim instance As SortedDictionary(Of TKey, TValue)
[SerializableAttribute]
public class SortedDictionary<TKey,TValue> : IDictionary<TKey,TValue>, ICollection<KeyValuePair<TKey,TValue>>,
IEnumerable<KeyValuePair<TKey,TValue>>, IDictionary, ICollection, IEnumerable
[SerializableAttribute]
generic<typename TKey, typename TValue>
public ref class SortedDictionary : IDictionary<TKey, TValue>, ICollection<KeyValuePair<TKey, TValue>>,
IEnumerable<KeyValuePair<TKey, TValue>>, IDictionary, ICollection, IEnumerable
J# 支持使用泛型类型和方法,但不支持进行新的声明。
类型参数
- TKey
字典中的键的类型。
- TValue
字典中的值的类型。
SortedDictionary 泛型类是检索运算复杂度为 O(log n) 的二叉搜索树,其中 n 是字典中的元素数。就这一点而言,它与 SortedList 泛型类相似。这两个类具有相似的对象模型,并且都具有 O(log n) 的检索运算复杂度。这两个类的区别在于内存的使用以及插入和移除元素的速度:
-
SortedList 使用的内存比 SortedDictionary 少。
-
SortedDictionary 可对未排序的数据执行更快的插入和移除操作:它的时间复杂度为 O(log n),而 SortedList 为 O(n)。
-
如果使用排序数据一次性填充列表,则 SortedList 比 SortedDictionary 快。
每个键/值对都可以作为 KeyValuePair 结构进行检索,或作为 DictionaryEntry 通过非泛型 IDictionary 接口进行检索。
只要键用作 SortedDictionary 中的键,它们就必须是不可变的。SortedDictionary 中的每个键必须是唯一的。键不能为 空引用(在 Visual Basic 中为 Nothing),但是如果值类型 TValue 为引用类型,该值则可以为空。
SortedDictionary 需要比较器实现来执行键比较。可以使用一个接受 comparer 参数的构造函数来指定 IComparer 泛型接口的实现;如果不指定实现,则使用默认的泛型比较器 Comparer.Default。如果类型 TKey 实现 System.IComparable 泛型接口,则默认比较器使用该实现。
C# 语言的 foreach 语句(在 C++ 中为 for each,在 Visual Basic 中为 For Each)需要集合中每个元素的类型。由于 SortedDictionary 的每个元素都是一个键/值对,因此元素类型既不是键的类型,也不是值的类型。而是 KeyValuePair 类型。下面的代码演示 C#、C++ 和 Visual Basic 语法。
foreach (KeyValuePair<int, string> kvp in myDictionary) {...}
for each (KeyValuePair<int, String^> kvp in myDictionary) {...}
For Each kvp As KeyValuePair(Of Integer, String) In myDictionary
...
Next myKVP
foreach 语句是对枚举数的包装,只允许该枚举数读取集合,而不允许写入集合。
下面的代码示例创建一个具有字符串键的字符串的空 SortedDictionary,并使用 Add 方法添加一些元素。该示例演示在尝试添加重复的键时 Add 方法引发 ArgumentException。
该示例使用 Item 属性(C# 中的索引器)检索值,演示当请求的键不存在时引发 KeyNotFoundException,以及可以替换与键关联的值。
该示例演示,如果程序必须经常尝试词典中不存在的键值,如何使用 TryGetValue 方法作为更有效的检索值的方法,该示例还演示在调用 Add 方法之前如何使用 ContainsKey 方法来测试键是否存在。
该示例演示如何枚举字典中的键和值,以及如何使用 Keys 属性和 Values 属性单独枚举键和值。
最后,该示例演示 Remove 方法。
Imports System
Imports System.Collections.Generic
Public Class Example
Public Shared Sub Main()
' Create a new dictionary of strings, with string keys.
'
Dim openWith As New Dictionary(Of String, String)
' Add some elements to the dictionary. There are no
' duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")
' The Add method throws an exception if the new key is
' already in the dictionary.
Try
openWith.Add("txt", "winword.exe")
Catch
Console.WriteLine("An element with Key = ""txt"" already exists.")
End Try
' 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 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.
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
' 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 you use foreach to enumerate dictionary elements,
' the elements are retrieved as KeyValuePair objects.
Console.WriteLine()
For Each kvp As KeyValuePair(Of String, String) In openWith
Console.WriteLine("Key = {0}, Value = {1}", _
kvp.Key, kvp.Value)
Next kvp
' To get the values alone, use the Values property.
Dim valueColl As _
Dictionary(Of String, String).ValueCollection = _
openWith.Values
' The elements of the ValueCollection are strongly typed
' with the type that was specified for dictionary values.
Console.WriteLine()
For Each s As String In valueColl
Console.WriteLine("Value = {0}", s)
Next s
' To get the keys alone, use the Keys property.
Dim keyColl As _
Dictionary(Of String, String).KeyCollection = _
openWith.Keys
' The elements of the KeyCollection are strongly typed
' with the type that was specified for dictionary keys.
Console.WriteLine()
For Each s As String In keyColl
Console.WriteLine("Key = {0}", s)
Next s
' Use the Remove method to remove a key/value pair.
Console.WriteLine(vbLf + "Remove(""doc"")")
openWith.Remove("doc")
If Not openWith.ContainsKey("doc") Then
Console.WriteLine("Key ""doc"" is not found.")
End If
End Sub
End Class
' This code example produces the following output:
'
'An element with Key = "txt" already exists.
'For key = "rtf", value = wordpad.exe.
'For key = "rtf", value = winword.exe.
'Key = "tif" is not found.
'Key = "tif" is not found.
'Value added for key = "ht": hypertrm.exe
'
'Key = txt, Value = notepad.exe
'Key = bmp, Value = paint.exe
'Key = dib, Value = paint.exe
'Key = rtf, Value = winword.exe
'Key = doc, Value = winword.exe
'Key = ht, Value = hypertrm.exe
'
'Value = notepad.exe
'Value = paint.exe
'Value = paint.exe
'Value = winword.exe
'Value = winword.exe
'Value = hypertrm.exe
'
'Key = txt
'Key = bmp
'Key = dib
'Key = rtf
'Key = doc
'Key = ht
'
'Remove("doc")
'Key "doc" is not found.
'
using System;
using System.Collections.Generic;
public class Example
{
public static void Main()
{
// Create a new dictionary of strings, with string keys.
//
Dictionary<string, string> openWith =
new Dictionary<string, string>();
// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
openWith.Add("bmp", "paint.exe");
openWith.Add("dib", "paint.exe");
openWith.Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the dictionary.
try
{
openWith.Add("txt", "winword.exe");
}
catch (ArgumentException)
{
Console.WriteLine("An element with Key = \"txt\" already exists.");
}
// 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 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.");
}
// 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.");
}
// 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 you use foreach to enumerate dictionary elements,
// the elements are retrieved as KeyValuePair objects.
Console.WriteLine();
foreach( KeyValuePair<string, string> kvp in openWith )
{
Console.WriteLine("Key = {0}, Value = {1}",
kvp.Key, kvp.Value);
}
// To get the values alone, use the Values property.
Dictionary<string, string>.ValueCollection valueColl =
openWith.Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console.WriteLine();
foreach( string s in valueColl )
{
Console.WriteLine("Value = {0}", s);
}
// To get the keys alone, use the Keys property.
Dictionary<string, string>.KeyCollection keyColl =
openWith.Keys;
// The elements of the KeyCollection are strongly typed
// with the type that was specified for dictionary keys.
Console.WriteLine();
foreach( string s in keyColl )
{
Console.WriteLine("Key = {0}", s);
}
// Use the Remove method to remove a key/value pair.
Console.WriteLine("\nRemove(\"doc\")");
openWith.Remove("doc");
if (!openWith.ContainsKey("doc"))
{
Console.WriteLine("Key \"doc\" is not found.");
}
}
}
/* This code example produces the following output:
An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Key = "tif" is not found.
Key = "tif" is not found.
Value added for key = "ht": hypertrm.exe
Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Key = ht, Value = hypertrm.exe
Value = notepad.exe
Value = paint.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Value = hypertrm.exe
Key = txt
Key = bmp
Key = dib
Key = rtf
Key = doc
Key = ht
Remove("doc")
Key "doc" is not found.
*/
System.Object
System.Collections.Generic.SortedDictionary
此类型的公共静态(在 Visual Basic 中为 Shared)成员是线程安全的。但不能保证任何实例成员是线程安全的。
只要不修改该集合,SortedDictionary 就可以同时支持多个阅读器。即便如此,从头到尾对一个集合进行枚举本质上并不是一个线程安全的过程。若要确保枚举过程中的线程安全,可以在整个枚举过程中锁定集合。若要允许多个线程访问集合以进行读写操作,则必须实现自己的同步。
Windows 98、Windows 2000 SP4、Windows Millennium Edition、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表,请参见系统要求。
.NET Framework
受以下版本支持:2.0