IDictionaryEnumerator Schnittstelle

Definition

Zählt die Elemente eines nicht generischen Wörterbuchs auf.Enumerates the elements of a nongeneric dictionary.

public interface class IDictionaryEnumerator : System::Collections::IEnumerator
[System.Runtime.InteropServices.ComVisible(true)]
public interface IDictionaryEnumerator : System.Collections.IEnumerator
type IDictionaryEnumerator = interface
    interface IEnumerator
Public Interface IDictionaryEnumerator
Implements IEnumerator
Abgeleitet
Attribute
Implementiert

Beispiele

Dieses Codebeispiel zeigt, wie Sie einen Wörterbuch Enumerator definieren, IDictionaryEnumerator der die-Schnittstelle implementiert.This code example shows how to define a dictionary enumerator that implements the IDictionaryEnumerator interface.

using namespace System;
using namespace System::Collections;

// This class implements a simple dictionary using an array of
// DictionaryEntry objects (key/value pairs).
public ref class SimpleDictionary : public IDictionary
{
    // The array of items
private:
    array<DictionaryEntry^>^ items;
private:
    int itemsInUse;

    // Construct the SimpleDictionary with the desired number of
    // items. The number of items cannot change for the life time of
    // this SimpleDictionary.
public:
    SimpleDictionary(int size)
    {
        items = gcnew array<DictionaryEntry^>(size);
    }

    #pragma region IDictionary Members
public:
    property virtual bool IsReadOnly
    {
        bool get()
        {
            return false;
        }
    }
public:
    virtual bool Contains(Object^ key)
    {
        int index;
        return TryGetIndexOfKey(key, &index);
    }
public:
    virtual property bool IsFixedSize
    {
        bool get()
        {
            return false;
        }
    }
public:
    virtual void Remove(Object^ key)
    {
        if (key == nullptr)
        {
            throw gcnew ArgumentNullException("key");
        }
        // Try to find the key in the DictionaryEntry array
        int index;
        if (TryGetIndexOfKey(key, &index))
        {
            // If the key is found, slide all the items down.
            Array::Copy(items, index + 1, items, index, itemsInUse -
                index - 1);
            itemsInUse--;
        }
        else
        {
            // If the key is not in the dictionary, just return.
            return;
        }
    }
public:
    virtual void Clear()
    {
        itemsInUse = 0;
    }
public:
    virtual void Add(Object^ key, Object^ value)
    {
        // Add the new key/value pair even if this key already exists
        // in the dictionary.
        if (itemsInUse == items->Length)
        {
            throw gcnew InvalidOperationException
                ("The dictionary cannot hold any more items.");
        }
        items[itemsInUse++] = gcnew DictionaryEntry(key, value);
    }
public:
    virtual property ICollection^ Keys
    {
        ICollection^ get()
        {
            // Return an array where each item is a key.
            array<Object^>^ keys = gcnew array<Object^>(itemsInUse);
            for (int i = 0; i < itemsInUse; i++)
            {
                keys[i] = items[i]->Key;
            }
            return keys;
        }
    }
public:
    virtual property ICollection^ Values
    {
        ICollection^ get()
        {
            // Return an array where each item is a value.
            array<Object^>^ values = gcnew array<Object^>(itemsInUse);
            for (int i = 0; i < itemsInUse; i++)
            {
                values[i] = items[i]->Value;
            }
            return values;
        }
    }
public:
    virtual property Object^ default[Object^]
    {
        Object^ get(Object^ key)
        {
            // If this key is in the dictionary, return its value.
            int index;
            if (TryGetIndexOfKey(key, &index))
            {
                // The key was found; return its value.
                return items[index]->Value;
            }
            else
            {
                // The key was not found; return null.
                return nullptr;
            }
        }

        void set(Object^ key, Object^ value)
        {
            // If this key is in the dictionary, change its value.
            int index;
            if (TryGetIndexOfKey(key, &index))
            {
                // The key was found; change its value.
                items[index]->Value = value;
            }
            else
            {
                // This key is not in the dictionary; add this
                // key/value pair.
                Add(key, value);
            }
        }
    }
private:
    bool TryGetIndexOfKey(Object^ key, int* index)
    {
        for (*index = 0; *index < itemsInUse; *index++)
        {
            // If the key is found, return true (the index is also
            // returned).
            if (items[*index]->Key->Equals(key))
            {
                return true;
            }
        }

        // Key not found, return false (index should be ignored by
        // the caller).
        return false;
    }
private:
    ref class SimpleDictionaryEnumerator : public IDictionaryEnumerator
    {
        // A copy of the SimpleDictionary object's key/value pairs.
private:
        array<DictionaryEntry^>^ items;
private:
        int index;

public:
        SimpleDictionaryEnumerator(SimpleDictionary^ sd)
        {
            // Make a copy of the dictionary entries currently in the
            // SimpleDictionary object.
            items = gcnew array<DictionaryEntry^>(sd->Count);
            Array::Copy(sd->items, 0, items, 0, sd->Count);
            index = -1;
        }

        // Return the current item.
public:
        virtual property Object^ Current
        {
            Object^ get()
            {
                ValidateIndex();
                return items[index];
            }
        }

        // Return the current dictionary entry.
public:
        virtual property DictionaryEntry Entry
        {
            DictionaryEntry get()
            {
                return (DictionaryEntry) Current;
            }
        }

        // Return the key of the current item.
public:
        virtual property Object^ Key
        {
            Object^ get()
            {
                ValidateIndex();
                return items[index]->Key;
            }
        }

        // Return the value of the current item.
public:
        virtual property Object^ Value
        {
            Object^ get()
            {
                ValidateIndex();
                return items[index]->Value;
            }
        }

        // Advance to the next item.
public:
        virtual bool MoveNext()
        {
            if (index < items->Length - 1)
            {
                index++;
                return true;
            }
            return false;
        }

        // Validate the enumeration index and throw an exception if
        // the index is out of range.
private:
        void ValidateIndex()
        {
            if (index < 0 || index >= items->Length)
            {
                throw gcnew InvalidOperationException
                    ("Enumerator is before or after the collection.");
            }
        }

        // Reset the index to restart the enumeration.
public:
        virtual void Reset()
        {
            index = -1;
        }
    };
public:
    virtual IDictionaryEnumerator^ GetEnumerator()
    {
        // Construct and return an enumerator.
        return gcnew SimpleDictionaryEnumerator(this);
    }
    #pragma endregion

    #pragma region ICollection Members
public:
    virtual property bool IsSynchronized
    {
        bool get()
        {
            return false;
        }
    }

public:
    virtual property Object^ SyncRoot
    {
        Object^ get()
        {
            throw gcnew NotImplementedException();
        }
    }

public:
    virtual property int Count
    {
        int get()
        {
            return itemsInUse;
        }
    }

public:
    virtual void CopyTo(Array^ array, int index)
    {
        throw gcnew NotImplementedException();
    }
    #pragma endregion

    #pragma region IEnumerable Members

    virtual IEnumerator^ IEnumerable_GetEnumerator() 
        = IEnumerable::GetEnumerator
    {
        // Construct and return an enumerator.
        return ((IDictionary^)this)->GetEnumerator();
    }
    #pragma endregion
};

int main()
{
    // Create a dictionary that contains no more than three
    // entries.
    IDictionary^ d = gcnew SimpleDictionary(3);

    // Add three people and their ages to the dictionary.
    d->Add("Jeff", 40);
    d->Add("Kristin", 34);
    d->Add("Aidan", 1);

    Console::WriteLine("Number of elements in dictionary = {0}",
        d->Count);

    Console::WriteLine("Does dictionary contain 'Jeff'? {0}",
        d->Contains("Jeff"));
    Console::WriteLine("Jeff's age is {0}", d["Jeff"]);

    // Display every entry's key and value.
    for each (DictionaryEntry^ de in d)
    {
        Console::WriteLine("{0} is {1} years old.", de->Key,
            de->Value);
    }

    // Remove an entry that exists.
    d->Remove("Jeff");

    // Remove an entry that does not exist, but do not throw an
    // exception.
    d->Remove("Max");

    // Show the names (keys) of the people in the dictionary.
    for each (String^ s in d->Keys)
    {
        Console::WriteLine(s);
    }

    // Show the ages (values) of the people in the dictionary.
    for each (int age in d->Values)
    {
        Console::WriteLine(age);
    }
}

// This code produces the following output.
//
// Number of elements in dictionary = 3
// Does dictionary contain 'Jeff'? True
// Jeff's age is 40
// Jeff is 40 years old.
// Kristin is 34 years old.
// Aidan is 1 years old.
// Kristin
// Aidan
// 34
// 1
using System;
using System.Collections;

// This class implements a simple dictionary using an array of DictionaryEntry objects (key/value pairs).
public class SimpleDictionary : IDictionary
{
    // The array of items
    private DictionaryEntry[] items;
    private Int32 ItemsInUse = 0;

    // Construct the SimpleDictionary with the desired number of items.
    // The number of items cannot change for the life time of this SimpleDictionary.
    public SimpleDictionary(Int32 numItems)
    {
        items = new DictionaryEntry[numItems];
    }


    #region IDictionary Members
    public bool IsReadOnly { get { return false; } }
    public bool Contains(object key)
    {
       Int32 index;
       return TryGetIndexOfKey(key, out index);
    }
    public bool IsFixedSize { get { return false; } }
    public void Remove(object key)
    {
        if (key == null) throw new ArgumentNullException("key");
        // Try to find the key in the DictionaryEntry array
        Int32 index;
        if (TryGetIndexOfKey(key, out index))
        {
            // If the key is found, slide all the items up.
            Array.Copy(items, index + 1, items, index, ItemsInUse - index - 1);
            ItemsInUse--;
        } 
        else
        {
            // If the key is not in the dictionary, just return. 
        }
    }
    public void Clear() { ItemsInUse = 0; }
    public void Add(object key, object value) 
    {
        // Add the new key/value pair even if this key already exists in the dictionary.
        if (ItemsInUse == items.Length)
            throw new InvalidOperationException("The dictionary cannot hold any more items.");
        items[ItemsInUse++] = new DictionaryEntry(key, value);
    }
    public ICollection Keys
    {
        get
        {
            // Return an array where each item is a key.
            Object[] keys = new Object[ItemsInUse];
            for (Int32 n = 0; n < ItemsInUse; n++)
                keys[n] = items[n].Key;
            return keys;
        }
    }
    public ICollection Values
    {
        get
        {
            // Return an array where each item is a value.
            Object[] values = new Object[ItemsInUse];
            for (Int32 n = 0; n < ItemsInUse; n++)
                values[n] = items[n].Value;
            return values;
        }
    }
    public object this[object key]
    {
        get
        {   
            // If this key is in the dictionary, return its value.
            Int32 index;
            if (TryGetIndexOfKey(key, out index))
            {
                // The key was found; return its value.
                return items[index].Value;
            } 
            else
            {
                // The key was not found; return null.
                return null;
            }
        }

        set
        {
            // If this key is in the dictionary, change its value. 
            Int32 index;
            if (TryGetIndexOfKey(key, out index))
            {
                // The key was found; change its value.
                items[index].Value = value;
            } 
            else
            {
                // This key is not in the dictionary; add this key/value pair.
                Add(key, value);
            }
        }
    }
    private Boolean TryGetIndexOfKey(Object key, out Int32 index)
    {
        for (index = 0; index < ItemsInUse; index++)
        {
            // If the key is found, return true (the index is also returned).
            if (items[index].Key.Equals(key)) return true;
        }
      
        // Key not found, return false (index should be ignored by the caller).
        return false;
    }
    private class SimpleDictionaryEnumerator : IDictionaryEnumerator
    {
        // A copy of the SimpleDictionary object's key/value pairs.
        DictionaryEntry[] items;
        Int32 index = -1;

        public SimpleDictionaryEnumerator(SimpleDictionary sd)
        {
            // Make a copy of the dictionary entries currently in the SimpleDictionary object.
            items = new DictionaryEntry[sd.Count];
            Array.Copy(sd.items, 0, items, 0, sd.Count);
        }

        // Return the current item.
        public Object Current { get { ValidateIndex(); return items[index]; } }

        // Return the current dictionary entry.
        public DictionaryEntry Entry
        {
            get { return (DictionaryEntry) Current; }
        }

        // Return the key of the current item.
        public Object Key { get { ValidateIndex();  return items[index].Key; } }

        // Return the value of the current item.
        public Object Value { get { ValidateIndex();  return items[index].Value; } }

        // Advance to the next item.
        public Boolean MoveNext()
        {
            if (index < items.Length - 1) { index++; return true; }
            return false;
        }

        // Validate the enumeration index and throw an exception if the index is out of range.
        private void ValidateIndex()
        {
            if (index < 0 || index >= items.Length)
            throw new InvalidOperationException("Enumerator is before or after the collection.");
        }

        // Reset the index to restart the enumeration.
        public void Reset()
        {
            index = -1;
        }
    }
    public IDictionaryEnumerator GetEnumerator()
    {
        // Construct and return an enumerator.
        return new SimpleDictionaryEnumerator(this);
    }
    #endregion

    #region ICollection Members
    public bool IsSynchronized { get { return false; } }
    public object SyncRoot { get { throw new NotImplementedException(); } }
    public int Count { get { return ItemsInUse; } }
    public void CopyTo(Array array, int index) { throw new NotImplementedException(); }
    #endregion

    #region IEnumerable Members
    IEnumerator IEnumerable.GetEnumerator() 
    {
        // Construct and return an enumerator.
        return ((IDictionary)this).GetEnumerator();
    }
    #endregion
}

public sealed class App
{
    static void Main()
    {
        // Create a dictionary that contains no more than three entries.
        IDictionary d = new SimpleDictionary(3);

        // Add three people and their ages to the dictionary.
        d.Add("Jeff", 40);
        d.Add("Kristin", 34);
        d.Add("Aidan", 1);

        Console.WriteLine("Number of elements in dictionary = {0}", d.Count);

        Console.WriteLine("Does dictionary contain 'Jeff'? {0}", d.Contains("Jeff"));
        Console.WriteLine("Jeff's age is {0}", d["Jeff"]);

        // Display every entry's key and value.
        foreach (DictionaryEntry de in d)
        {
            Console.WriteLine("{0} is {1} years old.", de.Key, de.Value);
        }

        // Remove an entry that exists.
        d.Remove("Jeff");

        // Remove an entry that does not exist, but do not throw an exception.
        d.Remove("Max");

        // Show the names (keys) of the people in the dictionary.
        foreach (String s in d.Keys)
            Console.WriteLine(s);

        // Show the ages (values) of the people in the dictionary.
        foreach (Int32 age in d.Values)
            Console.WriteLine(age);
    }
}

// This code produces the following output.
//
// Number of elements in dictionary = 3
// Does dictionary contain 'Jeff'? True
// Jeff's age is 40
// Jeff is 40 years old.
// Kristin is 34 years old.
// Aidan is 1 years old.
// Kristin
// Aidan
// 34
// 1
Imports System.Collections

' This class implements a simple dictionary using an array of DictionaryEntry objects (key/value pairs).
Public Class SimpleDictionary
    Implements IDictionary

    ' The array of items
    Dim items() As DictionaryEntry
    Dim ItemsInUse As Integer = 0

    ' Construct the SimpleDictionary with the desired number of items.
    ' The number of items cannot change for the life time of this SimpleDictionary.
    Public Sub New(ByVal numItems As Integer)
        items = New DictionaryEntry(numItems - 1) {}
    End Sub

    ' IDictionary Members
    Public ReadOnly Property IsReadOnly() As Boolean Implements IDictionary.IsReadOnly
        Get
            Return False
        End Get
    End Property

    Public Function Contains(ByVal key As Object) As Boolean Implements IDictionary.Contains
        Dim index As Integer
        Return TryGetIndexOfKey(key, index)
    End Function

    Public ReadOnly Property IsFixedSize() As Boolean Implements IDictionary.IsFixedSize
        Get
            Return False
        End Get
    End Property

    Public Sub Remove(ByVal key As Object) Implements IDictionary.Remove
        If key = Nothing Then
            Throw New ArgumentNullException("key")
        End If
        ' Try to find the key in the DictionaryEntry array
        Dim index As Integer
        If TryGetIndexOfKey(key, index) Then

            ' If the key is found, slide all the items up.
            Array.Copy(items, index + 1, items, index, (ItemsInUse - index) - 1)
            ItemsInUse = ItemsInUse - 1
        Else

            ' If the key is not in the dictionary, just return. 
        End If
    End Sub

    Public Sub Clear() Implements IDictionary.Clear
        ItemsInUse = 0
    End Sub

    Public Sub Add(ByVal key As Object, ByVal value As Object) Implements IDictionary.Add

        ' Add the new key/value pair even if this key already exists in the dictionary.
        If ItemsInUse = items.Length Then
            Throw New InvalidOperationException("The dictionary cannot hold any more items.")
        End If
        items(ItemsInUse) = New DictionaryEntry(key, value)
        ItemsInUse = ItemsInUse + 1
    End Sub

    Public ReadOnly Property Keys() As ICollection Implements IDictionary.Keys
        Get

            ' Return an array where each item is a key.
            ' Note: Declaring keyArray() to have a size of ItemsInUse - 1
            '       ensures that the array is properly sized, in VB.NET
            '       declaring an array of size N creates an array with
            '       0 through N elements, including N, as opposed to N - 1
            '       which is the default behavior in C# and C++.
            Dim keyArray() As Object = New Object(ItemsInUse - 1) {}
            Dim n As Integer
            For n = 0 To ItemsInUse - 1
                keyArray(n) = items(n).Key
            Next n

            Return keyArray
        End Get
    End Property

    Public ReadOnly Property Values() As ICollection Implements IDictionary.Values
        Get
            ' Return an array where each item is a value.
            Dim valueArray() As Object = New Object(ItemsInUse - 1) {}
            Dim n As Integer
            For n = 0 To ItemsInUse - 1
                valueArray(n) = items(n).Value
            Next n

            Return valueArray
        End Get
    End Property

    Public Property Item(ByVal key As Object) As Object Implements IDictionary.Item
        Get

            ' If this key is in the dictionary, return its value.
            Dim index As Integer
            If TryGetIndexOfKey(key, index) Then

                ' The key was found return its value.
                Return items(index).Value
            Else

                ' The key was not found return null.
                Return Nothing
            End If
        End Get

        Set(ByVal value As Object)
            ' If this key is in the dictionary, change its value. 
            Dim index As Integer
            If TryGetIndexOfKey(key, index) Then

                ' The key was found change its value.
                items(index).Value = value
            Else

                ' This key is not in the dictionary add this key/value pair.
                Add(key, value)
            End If
        End Set
    End Property

    Private Function TryGetIndexOfKey(ByVal key As Object, ByRef index As Integer) As Boolean
        For index = 0 To ItemsInUse - 1
            ' If the key is found, return true (the index is also returned).
            If items(index).Key.Equals(key) Then
                Return True
            End If
        Next index

        ' Key not found, return false (index should be ignored by the caller).
        Return False
    End Function

    Private Class SimpleDictionaryEnumerator
        Implements IDictionaryEnumerator

        ' A copy of the SimpleDictionary object's key/value pairs.
        Dim items() As DictionaryEntry
        Dim index As Integer = -1

        Public Sub New(ByVal sd As SimpleDictionary)
            ' Make a copy of the dictionary entries currently in the SimpleDictionary object.
            items = New DictionaryEntry(sd.Count - 1) {}
            Array.Copy(sd.items, 0, items, 0, sd.Count)
        End Sub

        ' Return the current item.
        Public ReadOnly Property Current() As Object Implements IDictionaryEnumerator.Current
            Get
                ValidateIndex()
                Return items(index)
            End Get
        End Property

        ' Return the current dictionary entry.
        Public ReadOnly Property Entry() As DictionaryEntry Implements IDictionaryEnumerator.Entry
            Get
                Return Current
            End Get
        End Property

        ' Return the key of the current item.
        Public ReadOnly Property Key() As Object Implements IDictionaryEnumerator.Key
            Get
                ValidateIndex()
                Return items(index).Key
            End Get
        End Property

        ' Return the value of the current item.
        Public ReadOnly Property Value() As Object Implements IDictionaryEnumerator.Value
            Get
                ValidateIndex()
                Return items(index).Value
            End Get
        End Property

        ' Advance to the next item.
        Public Function MoveNext() As Boolean Implements IDictionaryEnumerator.MoveNext
            If index < items.Length - 1 Then
                index = index + 1
                Return True
            End If

            Return False
        End Function

        ' Validate the enumeration index and throw an exception if the index is out of range.
        Private Sub ValidateIndex()
            If index < 0 Or index >= items.Length Then
                Throw New InvalidOperationException("Enumerator is before or after the collection.")
            End If
        End Sub

        ' Reset the index to restart the enumeration.
        Public Sub Reset() Implements IDictionaryEnumerator.Reset
            index = -1
        End Sub

    End Class

    Public Function GetEnumerator() As IDictionaryEnumerator Implements IDictionary.GetEnumerator

        'Construct and return an enumerator.
        Return New SimpleDictionaryEnumerator(Me)
    End Function


    ' ICollection Members
    Public ReadOnly Property IsSynchronized() As Boolean Implements IDictionary.IsSynchronized
        Get
            Return False
        End Get
    End Property

    Public ReadOnly Property SyncRoot() As Object Implements IDictionary.SyncRoot
        Get
            Throw New NotImplementedException()
        End Get
    End Property

    Public ReadOnly Property Count() As Integer Implements IDictionary.Count
        Get
            Return ItemsInUse
        End Get
    End Property

    Public Sub CopyTo(ByVal array As Array, ByVal index As Integer) Implements IDictionary.CopyTo
        Throw New NotImplementedException()
    End Sub

    ' IEnumerable Members
    Public Function GetEnumerator1() As IEnumerator Implements IEnumerable.GetEnumerator

        ' Construct and return an enumerator.
        Return Me.GetEnumerator()
    End Function
End Class

Public NotInheritable Class App
    Public Shared Sub Main()
        ' Create a dictionary that contains no more than three entries.
        Dim d As IDictionary = New SimpleDictionary(3)

        ' Add three people and their ages to the dictionary.
        d.Add("Jeff", 40)
        d.Add("Kristin", 34)
        d.Add("Aidan", 1)

        Console.WriteLine("Number of elements in dictionary = {0}", d.Count)

        Console.WriteLine("Does dictionary contain 'Jeff'? {0}", d.Contains("Jeff"))
        Console.WriteLine("Jeff's age is {0}", d("Jeff"))

        ' Display every entry's key and value.
        Dim de As DictionaryEntry
        For Each de In d
            Console.WriteLine("{0} is {1} years old.", de.Key, de.Value)
        Next

        ' Remove an entry that exists.
        d.Remove("Jeff")

        ' Remove an entry that does not exist, but do not throw an exception.
        d.Remove("Max")

        ' Show the names (keys) of the people in the dictionary.
        Dim s As String

        For Each s In d.Keys
            Console.WriteLine(s)
        Next

        ' Show the ages (values) of the people in the dictionary.
        Dim age As Integer
        For Each age In d.Values
            Console.WriteLine(age)
        Next

    End Sub
End Class

' This code produces the following output.
'
' Number of elements in dictionary = 3
' Does dictionary contain 'Jeff'? True
' Jeff's age is 40
' Jeff is 40 years old.
' Kristin is 34 years old.
' Aidan is 1 years old.
' Kristin
' Aidan
' 34
' 1

Hinweise

Die foreach-Anweisung der Programmiersprache C# (for each in Visual Basic) verbirgt die Komplexität der Enumeratoren.The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. Daher wird die foreach Verwendung von empfohlen, anstatt den Enumerator direkt zu manipulieren.Therefore, using foreach is recommended instead of directly manipulating the enumerator.

Mit Enumeratoren können die Daten in der Auflistung zwar gelesen, jedoch nicht zum Ändern der zugrunde liegenden Auflistung verwendet werden.Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

Zu Beginn wird der Enumerator vor das erste Element in der Auflistung positioniert.Initially, the enumerator is positioned before the first element in the collection. Die Reset -Methode bringt den Enumerator auch wieder auf diese Position zurück.The Reset method also brings the enumerator back to this position. An dieser Position ist Current nicht definiert.At this position, Current is undefined. Daher muss die MoveNext -Methode aufgerufen werden, um den Enumerator vor dem Lesen des Werts von Currentauf das erste Element der Auflistung zu setzen.Therefore, you must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Current.

Current gibt solange dasselbe Objekt zurück, bis MoveNext oder Reset aufgerufen wird.Current returns the same object until either MoveNext or Reset is called. MoveNext legt Current auf das nächste Element fest.MoveNext sets Current to the next element.

Wenn MoveNext das Ende der Auflistung übergibt, wird der Enumerator hinter dem letzten Element in der Auflistung platziert, und MoveNext gibt false zurück.If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. Wenn sich der Enumerator an dieser Position befindet, geben nachfolgende Aufrufe von MoveNext auch false zurück.When the enumerator is at this position, subsequent calls to MoveNext also return false. Wenn der letzte Aufruf MoveNext zurückgegebene false, Current ist nicht definiert.If the last call to MoveNext returned false, Current is undefined. Um Current wieder auf das erste Element der Auflistung festzulegen, können Sie Reset gefolgt von MoveNext aufrufen.To set Current to the first element of the collection again, you can call Reset followed by MoveNext.

Ein Enumerator bleibt gültig, solange die Auflistung unverändert ist.An enumerator remains valid as long as the collection remains unchanged. Wenn an der Auflistung Änderungen vorgenommen werden, z. b. das Hinzufügen, ändern oder Löschen von Elementen, wird der Enumerator unwiederbringlich ungültig, MoveNext und Reset der nächste InvalidOperationExceptionRückruf von oder löst eine aus.If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException.

Der Enumerator hat keinen exklusiven Zugriff auf die Auflistung; daher ist die Enumeration einer Auflistung systembedingt kein threadsicheres Verfahren.The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. Selbst wenn eine Auflistung synchronisiert wird, besteht die Möglichkeit, dass andere Threads sie ändern. Dies führt dazu, dass der Enumerator eine Ausnahme auslöst.Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. Um während der Enumeration Threadsicherheit zu gewährleisten, können Sie entweder die Auflistung während der gesamten Enumeration sperren oder die Ausnahmen, die aus von anderen Threads stammenden Änderungen resultieren, abfangen.To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Hinweise für Ausführende

Die Current Object DictionaryEntryvon IEnumerator geerbte-Eigenschaft gibt ein-Objekt zurück, das ein geschachtelt ist.The Current property that is inherited from IEnumerator returns an Object that is a boxed DictionaryEntry. Sie ähnelt der-Eigenschaft Entry , mit der Ausnahme Entry , dass DictionaryEntry eine anstelle von Objectzurückgibt.It is similar to the Entry property, except that Entry returns a DictionaryEntry rather than an Object.

Eigenschaften

Current

Ruft das Element in der Auflistung an der aktuellen Position des Enumerators ab.Gets the element in the collection at the current position of the enumerator.

(Geerbt von IEnumerator)
Entry

Ruft sowohl den Schlüssel als auch den Wert des aktuellen Wörterbucheintrags ab.Gets both the key and the value of the current dictionary entry.

Key

Ruft den Schlüssel des aktuellen Wörterbucheintrags ab.Gets the key of the current dictionary entry.

Value

Ruft den Wert des aktuellen Wörterbucheintrags ab.Gets the value of the current dictionary entry.

Methoden

MoveNext()

Setzt den Enumerator auf das nächste Element der Auflistung.Advances the enumerator to the next element of the collection.

(Geerbt von IEnumerator)
Reset()

Setzt den Enumerator auf seine anfängliche Position vor dem ersten Element in der Auflistung.Sets the enumerator to its initial position, which is before the first element in the collection.

(Geerbt von IEnumerator)

Gilt für:

Siehe auch