IDictionaryEnumerator Interface
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Enumerates the elements of a nongeneric dictionary.
public interface class IDictionaryEnumerator : System::Collections::IEnumeratorpublic interface IDictionaryEnumerator : System.Collections.IEnumerator[System.Runtime.InteropServices.ComVisible(true)]
public interface IDictionaryEnumerator : System.Collections.IEnumeratortype IDictionaryEnumerator = interface
interface IEnumerator[<System.Runtime.InteropServices.ComVisible(true)>]
type IDictionaryEnumerator = interface
interface IEnumeratorPublic Interface IDictionaryEnumerator
Implements IEnumerator- Derived
- Attributes
- Implements
Examples
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
Remarks
The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. Therefore, using foreach is recommended instead of directly manipulating the enumerator.
Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.
Initially, the enumerator is positioned before the first element in the collection. The Reset method also brings the enumerator back to this position. At this position, Current is undefined. 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 returns the same object until either MoveNext or Reset is called. MoveNext sets Current to the next element.
If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. When the enumerator is at this position, subsequent calls to MoveNext also return false. If the last call to MoveNext returned false, Current is undefined. To set Current to the first element of the collection again, you can call Reset followed by MoveNext.
An enumerator remains valid as long as the collection remains unchanged. 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.
The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 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.
Notes to Implementers
The Current property that is inherited from IEnumerator returns an Object that is a boxed DictionaryEntry. It is similar to the Entry property, except that Entry returns a DictionaryEntry rather than an Object.
Properties
| Current |
Gets the element in the collection at the current position of the enumerator. (Inherited from IEnumerator) |
| Entry |
Gets both the key and the value of the current dictionary entry. |
| Key |
Gets the key of the current dictionary entry. |
| Value |
Gets the value of the current dictionary entry. |
Methods
| MoveNext() |
Advances the enumerator to the next element of the collection. (Inherited from IEnumerator) |
| Reset() |
Sets the enumerator to its initial position, which is before the first element in the collection. (Inherited from IEnumerator) |
Applies to
See also
Collaborate with us on GitHub
The source for this content can be found on GitHub, where you can also create and review issues and pull requests. For more information, see our contributor guide.
