DictionaryBase.GetEnumerator 方法
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
傳回能夠逐一查看 IDictionaryEnumerator 執行個體的 DictionaryBase。
public:
virtual System::Collections::IDictionaryEnumerator ^ GetEnumerator();public System.Collections.IDictionaryEnumerator GetEnumerator ();abstract member GetEnumerator : unit -> System.Collections.IDictionaryEnumerator
override this.GetEnumerator : unit -> System.Collections.IDictionaryEnumeratorPublic Function GetEnumerator () As IDictionaryEnumerator傳回
IDictionaryEnumerator 執行個體的 DictionaryBase。
實作
範例
下列程式代碼範例會實作 DictionaryBase 類別，並使用該實作來建立索引Length鍵和值為 5 個字元或更少值的字典String。
using namespace System;
using namespace System::Collections;
public ref class ShortStringDictionary: public DictionaryBase
{
public:
property String^ Item [String^]
{
String^ get( String^ key )
{
return (dynamic_cast<String^>(Dictionary[ key ]));
}
void set( String^ value, String^ key )
{
Dictionary[ key ] = value;
}
}
property ICollection^ Keys
{
ICollection^ get()
{
return (Dictionary->Keys);
}
}
property ICollection^ Values
{
ICollection^ get()
{
return (Dictionary->Values);
}
}
void Add( String^ key, String^ value )
{
Dictionary->Add( key, value );
}
bool Contains( String^ key )
{
return (Dictionary->Contains( key ));
}
void Remove( String^ key )
{
Dictionary->Remove( key );
}
protected:
virtual void OnInsert( Object^ key, Object^ value ) override
{
if ( key->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "key must be of type String.","key" );
else
{
String^ strKey = dynamic_cast<String^>(key);
if ( strKey->Length > 5 )
throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" );
}
if ( value->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "value must be of type String.","value" );
else
{
String^ strValue = dynamic_cast<String^>(value);
if ( strValue->Length > 5 )
throw gcnew ArgumentException( "value must be no more than 5 characters in length.","value" );
}
}
virtual void OnRemove( Object^ key, Object^ /*value*/ ) override
{
if ( key->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "key must be of type String.","key" );
else
{
String^ strKey = dynamic_cast<String^>(key);
if ( strKey->Length > 5 )
throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" );
}
}
virtual void OnSet( Object^ key, Object^ /*oldValue*/, Object^ newValue ) override
{
if ( key->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "key must be of type String.","key" );
else
{
String^ strKey = dynamic_cast<String^>(key);
if ( strKey->Length > 5 )
throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" );
}
if ( newValue->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "newValue must be of type String.","newValue" );
else
{
String^ strValue = dynamic_cast<String^>(newValue);
if ( strValue->Length > 5 )
throw gcnew ArgumentException( "newValue must be no more than 5 characters in length.","newValue" );
}
}
virtual void OnValidate( Object^ key, Object^ value ) override
{
if ( key->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "key must be of type String.","key" );
else
{
String^ strKey = dynamic_cast<String^>(key);
if ( strKey->Length > 5 )
throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" );
}
if ( value->GetType() != Type::GetType( "System.String" ) )
throw gcnew ArgumentException( "value must be of type String.","value" );
else
{
String^ strValue = dynamic_cast<String^>(value);
if ( strValue->Length > 5 )
throw gcnew ArgumentException( "value must be no more than 5 characters in length.","value" );
}
}
};
void PrintKeysAndValues2( ShortStringDictionary^ myCol );
void PrintKeysAndValues3( ShortStringDictionary^ myCol );
int main()
{
// Creates and initializes a new DictionaryBase.
ShortStringDictionary^ mySSC = gcnew ShortStringDictionary;
// Adds elements to the collection.
mySSC->Add( "One", "a" );
mySSC->Add( "Two", "ab" );
mySSC->Add( "Three", "abc" );
mySSC->Add( "Four", "abcd" );
mySSC->Add( "Five", "abcde" );
// Display the contents of the collection using the enumerator.
Console::WriteLine( "Contents of the collection (using enumerator):" );
PrintKeysAndValues2( mySSC );
// Display the contents of the collection using the Keys property and the Item property.
Console::WriteLine( "Initial contents of the collection (using Keys and Item):" );
PrintKeysAndValues3( mySSC );
// Tries to add a value that is too long.
try
{
mySSC->Add( "Ten", "abcdefghij" );
}
catch ( ArgumentException^ e )
{
Console::WriteLine( e );
}
// Tries to add a key that is too long.
try
{
mySSC->Add( "Eleven", "ijk" );
}
catch ( ArgumentException^ e )
{
Console::WriteLine( e );
}
Console::WriteLine();
// Searches the collection with Contains.
Console::WriteLine( "Contains \"Three\": {0}", mySSC->Contains( "Three" ) );
Console::WriteLine( "Contains \"Twelve\": {0}", mySSC->Contains( "Twelve" ) );
Console::WriteLine();
// Removes an element from the collection.
mySSC->Remove( "Two" );
// Displays the contents of the collection.
Console::WriteLine( "After removing \"Two\":" );
PrintKeysAndValues2( mySSC );
}
// Uses the enumerator.
void PrintKeysAndValues2( ShortStringDictionary^ myCol )
{
DictionaryEntry myDE;
System::Collections::IEnumerator^ myEnumerator = myCol->GetEnumerator();
while ( myEnumerator->MoveNext() )
if ( myEnumerator->Current != nullptr )
{
myDE = *dynamic_cast<DictionaryEntry^>(myEnumerator->Current);
Console::WriteLine( " {0,-5} : {1}", myDE.Key, myDE.Value );
}
Console::WriteLine();
}
// Uses the Keys property and the Item property.
void PrintKeysAndValues3( ShortStringDictionary^ myCol )
{
ICollection^ myKeys = myCol->Keys;
IEnumerator^ myEnum1 = myKeys->GetEnumerator();
while ( myEnum1->MoveNext() )
{
String^ k = safe_cast<String^>(myEnum1->Current);
Console::WriteLine( " {0,-5} : {1}", k, myCol->Item[ k ] );
}
Console::WriteLine();
}
/*
This code produces the following output.
Contents of the collection (using enumerator):
Three : abc
Five : abcde
Two : ab
One : a
Four : abcd
Initial contents of the collection (using Keys and Item):
Three : abc
Five : abcde
Two : ab
One : a
Four : abcd
System.ArgumentException: value must be no more than 5 characters in length.
Parameter name: value
at ShortStringDictionary.OnValidate(Object key, Object value)
at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value)
at SamplesDictionaryBase.Main()
System.ArgumentException: key must be no more than 5 characters in length.
Parameter name: key
at ShortStringDictionary.OnValidate(Object key, Object value)
at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value)
at SamplesDictionaryBase.Main()
Contains "Three": True
Contains "Twelve": False
After removing "Two":
Three : abc
Five : abcde
One : a
Four : abcd
*/
using System;
using System.Collections;
public class ShortStringDictionary : DictionaryBase {
public String this[ String key ] {
get {
return( (String) Dictionary[key] );
}
set {
Dictionary[key] = value;
}
}
public ICollection Keys {
get {
return( Dictionary.Keys );
}
}
public ICollection Values {
get {
return( Dictionary.Values );
}
}
public void Add( String key, String value ) {
Dictionary.Add( key, value );
}
public bool Contains( String key ) {
return( Dictionary.Contains( key ) );
}
public void Remove( String key ) {
Dictionary.Remove( key );
}
protected override void OnInsert( Object key, Object value ) {
if ( key.GetType() != typeof(System.String) )
{
throw new ArgumentException( "key must be of type String.", "key" );
}
else {
String strKey = (String) key;
if ( strKey.Length > 5 )
throw new ArgumentException( "key must be no more than 5 characters in length.", "key" );
}
if ( value.GetType() != typeof(System.String) )
{
throw new ArgumentException( "value must be of type String.", "value" );
}
else {
String strValue = (String) value;
if ( strValue.Length > 5 )
throw new ArgumentException( "value must be no more than 5 characters in length.", "value" );
}
}
protected override void OnRemove( Object key, Object value ) {
if ( key.GetType() != typeof(System.String) )
{
throw new ArgumentException( "key must be of type String.", "key" );
}
else {
String strKey = (String) key;
if ( strKey.Length > 5 )
throw new ArgumentException( "key must be no more than 5 characters in length.", "key" );
}
}
protected override void OnSet( Object key, Object oldValue, Object newValue ) {
if ( key.GetType() != typeof(System.String) )
{
throw new ArgumentException( "key must be of type String.", "key" );
}
else {
String strKey = (String) key;
if ( strKey.Length > 5 )
throw new ArgumentException( "key must be no more than 5 characters in length.", "key" );
}
if ( newValue.GetType() != typeof(System.String) )
{
throw new ArgumentException( "newValue must be of type String.", "newValue" );
}
else {
String strValue = (String) newValue;
if ( strValue.Length > 5 )
throw new ArgumentException( "newValue must be no more than 5 characters in length.", "newValue" );
}
}
protected override void OnValidate( Object key, Object value ) {
if ( key.GetType() != typeof(System.String) )
{
throw new ArgumentException( "key must be of type String.", "key" );
}
else {
String strKey = (String) key;
if ( strKey.Length > 5 )
throw new ArgumentException( "key must be no more than 5 characters in length.", "key" );
}
if ( value.GetType() != typeof(System.String) )
{
throw new ArgumentException( "value must be of type String.", "value" );
}
else {
String strValue = (String) value;
if ( strValue.Length > 5 )
throw new ArgumentException( "value must be no more than 5 characters in length.", "value" );
}
}
}
public class SamplesDictionaryBase {
public static void Main() {
// Creates and initializes a new DictionaryBase.
ShortStringDictionary mySSC = new ShortStringDictionary();
// Adds elements to the collection.
mySSC.Add( "One", "a" );
mySSC.Add( "Two", "ab" );
mySSC.Add( "Three", "abc" );
mySSC.Add( "Four", "abcd" );
mySSC.Add( "Five", "abcde" );
// Display the contents of the collection using foreach. This is the preferred method.
Console.WriteLine( "Contents of the collection (using foreach):" );
PrintKeysAndValues1( mySSC );
// Display the contents of the collection using the enumerator.
Console.WriteLine( "Contents of the collection (using enumerator):" );
PrintKeysAndValues2( mySSC );
// Display the contents of the collection using the Keys property and the Item property.
Console.WriteLine( "Initial contents of the collection (using Keys and Item):" );
PrintKeysAndValues3( mySSC );
// Tries to add a value that is too long.
try {
mySSC.Add( "Ten", "abcdefghij" );
}
catch ( ArgumentException e ) {
Console.WriteLine( e.ToString() );
}
// Tries to add a key that is too long.
try {
mySSC.Add( "Eleven", "ijk" );
}
catch ( ArgumentException e ) {
Console.WriteLine( e.ToString() );
}
Console.WriteLine();
// Searches the collection with Contains.
Console.WriteLine( "Contains \"Three\": {0}", mySSC.Contains( "Three" ) );
Console.WriteLine( "Contains \"Twelve\": {0}", mySSC.Contains( "Twelve" ) );
Console.WriteLine();
// Removes an element from the collection.
mySSC.Remove( "Two" );
// Displays the contents of the collection.
Console.WriteLine( "After removing \"Two\":" );
PrintKeysAndValues1( mySSC );
}
// Uses the foreach statement which hides the complexity of the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
public static void PrintKeysAndValues1( ShortStringDictionary myCol ) {
foreach ( DictionaryEntry myDE in myCol )
Console.WriteLine( " {0,-5} : {1}", myDE.Key, myDE.Value );
Console.WriteLine();
}
// Uses the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
public static void PrintKeysAndValues2( ShortStringDictionary myCol ) {
DictionaryEntry myDE;
System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
while ( myEnumerator.MoveNext() )
if ( myEnumerator.Current != null ) {
myDE = (DictionaryEntry) myEnumerator.Current;
Console.WriteLine( " {0,-5} : {1}", myDE.Key, myDE.Value );
}
Console.WriteLine();
}
// Uses the Keys property and the Item property.
public static void PrintKeysAndValues3( ShortStringDictionary myCol ) {
ICollection myKeys = myCol.Keys;
foreach ( String k in myKeys )
Console.WriteLine( " {0,-5} : {1}", k, myCol[k] );
Console.WriteLine();
}
}
/*
This code produces the following output.
Contents of the collection (using foreach):
Three : abc
Five : abcde
Two : ab
One : a
Four : abcd
Contents of the collection (using enumerator):
Three : abc
Five : abcde
Two : ab
One : a
Four : abcd
Initial contents of the collection (using Keys and Item):
Three : abc
Five : abcde
Two : ab
One : a
Four : abcd
System.ArgumentException: value must be no more than 5 characters in length.
Parameter name: value
at ShortStringDictionary.OnValidate(Object key, Object value)
at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value)
at SamplesDictionaryBase.Main()
System.ArgumentException: key must be no more than 5 characters in length.
Parameter name: key
at ShortStringDictionary.OnValidate(Object key, Object value)
at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value)
at SamplesDictionaryBase.Main()
Contains "Three": True
Contains "Twelve": False
After removing "Two":
Three : abc
Five : abcde
One : a
Four : abcd
*/
Imports System.Collections
Public Class ShortStringDictionary
Inherits DictionaryBase
Default Public Property Item(key As String) As String
Get
Return CType(Dictionary(key), String)
End Get
Set
Dictionary(key) = value
End Set
End Property
Public ReadOnly Property Keys() As ICollection
Get
Return Dictionary.Keys
End Get
End Property
Public ReadOnly Property Values() As ICollection
Get
Return Dictionary.Values
End Get
End Property
Public Sub Add(key As String, value As String)
Dictionary.Add(key, value)
End Sub
Public Function Contains(key As String) As Boolean
Return Dictionary.Contains(key)
End Function 'Contains
Public Sub Remove(key As String)
Dictionary.Remove(key)
End Sub
Protected Overrides Sub OnInsert(key As Object, value As Object)
If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then
Throw New ArgumentException("key must be of type String.", "key")
Else
Dim strKey As String = CType(key, String)
If strKey.Length > 5 Then
Throw New ArgumentException("key must be no more than 5 characters in length.", "key")
End If
End If
If Not GetType(System.String).IsAssignableFrom(value.GetType()) Then
Throw New ArgumentException("value must be of type String.", "value")
Else
Dim strValue As String = CType(value, String)
If strValue.Length > 5 Then
Throw New ArgumentException("value must be no more than 5 characters in length.", "value")
End If
End If
End Sub
Protected Overrides Sub OnRemove(key As Object, value As Object)
If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then
Throw New ArgumentException("key must be of type String.", "key")
Else
Dim strKey As String = CType(key, String)
If strKey.Length > 5 Then
Throw New ArgumentException("key must be no more than 5 characters in length.", "key")
End If
End If
End Sub
Protected Overrides Sub OnSet(key As Object, oldValue As Object, newValue As Object)
If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then
Throw New ArgumentException("key must be of type String.", "key")
Else
Dim strKey As String = CType(key, String)
If strKey.Length > 5 Then
Throw New ArgumentException("key must be no more than 5 characters in length.", "key")
End If
End If
If Not GetType(System.String).IsAssignableFrom(newValue.GetType()) Then
Throw New ArgumentException("newValue must be of type String.", "newValue")
Else
Dim strValue As String = CType(newValue, String)
If strValue.Length > 5 Then
Throw New ArgumentException("newValue must be no more than 5 characters in length.", "newValue")
End If
End If
End Sub
Protected Overrides Sub OnValidate(key As Object, value As Object)
If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then
Throw New ArgumentException("key must be of type String.", "key")
Else
Dim strKey As String = CType(key, String)
If strKey.Length > 5 Then
Throw New ArgumentException("key must be no more than 5 characters in length.", "key")
End If
End If
If Not GetType(System.String).IsAssignableFrom(value.GetType()) Then
Throw New ArgumentException("value must be of type String.", "value")
Else
Dim strValue As String = CType(value, String)
If strValue.Length > 5 Then
Throw New ArgumentException("value must be no more than 5 characters in length.", "value")
End If
End If
End Sub
End Class
Public Class SamplesDictionaryBase
Public Shared Sub Main()
' Creates and initializes a new DictionaryBase.
Dim mySSC As New ShortStringDictionary()
' Adds elements to the collection.
mySSC.Add("One", "a")
mySSC.Add("Two", "ab")
mySSC.Add("Three", "abc")
mySSC.Add("Four", "abcd")
mySSC.Add("Five", "abcde")
' Display the contents of the collection using For Each. This is the preferred method.
Console.WriteLine("Contents of the collection (using For Each):")
PrintKeysAndValues1(mySSC)
' Display the contents of the collection using the enumerator.
Console.WriteLine("Contents of the collection (using enumerator):")
PrintKeysAndValues2(mySSC)
' Display the contents of the collection using the Keys property and the Item property.
Console.WriteLine("Initial contents of the collection (using Keys and Item):")
PrintKeysAndValues3(mySSC)
' Tries to add a value that is too long.
Try
mySSC.Add("Ten", "abcdefghij")
Catch e As ArgumentException
Console.WriteLine(e.ToString())
End Try
' Tries to add a key that is too long.
Try
mySSC.Add("Eleven", "ijk")
Catch e As ArgumentException
Console.WriteLine(e.ToString())
End Try
Console.WriteLine()
' Searches the collection with Contains.
Console.WriteLine("Contains ""Three"": {0}", mySSC.Contains("Three"))
Console.WriteLine("Contains ""Twelve"": {0}", mySSC.Contains("Twelve"))
Console.WriteLine()
' Removes an element from the collection.
mySSC.Remove("Two")
' Displays the contents of the collection.
Console.WriteLine("After removing ""Two"":")
PrintKeysAndValues1(mySSC)
End Sub
' Uses the For Each statement which hides the complexity of the enumerator.
' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
Public Shared Sub PrintKeysAndValues1(myCol As ShortStringDictionary)
Dim myDE As DictionaryEntry
For Each myDE In myCol
Console.WriteLine(" {0,-5} : {1}", myDE.Key, myDE.Value)
Next myDE
Console.WriteLine()
End Sub
' Uses the enumerator.
' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
Public Shared Sub PrintKeysAndValues2(myCol As ShortStringDictionary)
Dim myDE As DictionaryEntry
Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator()
While myEnumerator.MoveNext()
If Not (myEnumerator.Current Is Nothing) Then
myDE = CType(myEnumerator.Current, DictionaryEntry)
Console.WriteLine(" {0,-5} : {1}", myDE.Key, myDE.Value)
End If
End While
Console.WriteLine()
End Sub
' Uses the Keys property and the Item property.
Public Shared Sub PrintKeysAndValues3(myCol As ShortStringDictionary)
Dim myKeys As ICollection = myCol.Keys
Dim k As String
For Each k In myKeys
Console.WriteLine(" {0,-5} : {1}", k, myCol(k))
Next k
Console.WriteLine()
End Sub
End Class
'This code produces the following output.
'
'Contents of the collection (using For Each):
' Three : abc
' Five : abcde
' Two : ab
' One : a
' Four : abcd
'
'Contents of the collection (using enumerator):
' Three : abc
' Five : abcde
' Two : ab
' One : a
' Four : abcd
'
'Initial contents of the collection (using Keys and Item):
' Three : abc
' Five : abcde
' Two : ab
' One : a
' Four : abcd
'
'System.ArgumentException: value must be no more than 5 characters in length.
'Parameter name: value
' at ShortStringDictionary.OnValidate(Object key, Object value)
' at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value)
' at SamplesDictionaryBase.Main()
'System.ArgumentException: key must be no more than 5 characters in length.
'Parameter name: key
' at ShortStringDictionary.OnValidate(Object key, Object value)
' at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value)
' at SamplesDictionaryBase.Main()
'
'Contains "Three": True
'Contains "Twelve": False
'
'After removing "Two":
' Three : abc
' Five : abcde
' One : a
' Four : abcd
備註
C# 語言的 foreach 陳述式 (在 Visual Basic 中為 for each) 會隱藏列舉值的複雜度。 因此，建議您使用 foreach，而不要直接使用列舉值。
列舉程式可以用來讀取集合中的資料，但是無法用來修改基礎集合。
一開始，列舉程式位在集合中的第一個項目之前。 Reset 也會將列舉值帶回至這個位置。 在這個位置上，Current 並未定義。 因此，在讀取 MoveNext 的值之前，必須呼叫 Current 以將列舉值前移至集合的第一個項目。
Current 會傳回相同的物件直到呼叫 MoveNext 或 Reset。 MoveNext 會將 Current 設定為下一個項目。
如果 MoveNext 傳遞集合的結尾，列舉值會放置在集合的最後一個專案後面，並 MoveNext 傳 false回 。 當列舉值位於這個位置時，後續呼叫 MoveNext 也會傳回 false。 如果最後一次 MoveNext 呼叫傳 false回 ， Current 則為未定義。 若要再次將 Current 設定為集合的第一個元素，您可以在呼叫 Reset 之後，接著呼叫 MoveNext。
只要集合維持不變，列舉值就仍維持有效。 如果對集合進行變更，例如加入、修改或刪除項目，列舉程式會永久失效，且其行為未定義。
列舉程式沒有集合的獨佔存取權，因此，列舉集合內容本質上並不是安全的執行緒程序。 若要確保列舉期間的執行緒安全性，您可以在整個列舉期間鎖定集合。 若要讓多重執行緒能夠存取集合以便進行讀取和寫入，您必須實作自己的同步處理。
這個方法是 O(1) 作業。
適用於
另請參閱
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