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DictionaryBase.GetEnumerator Method

Returns an IDictionaryEnumerator that iterates through the DictionaryBase instance.

Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)

public IDictionaryEnumerator GetEnumerator ()
public final IDictionaryEnumerator GetEnumerator ()
public final function GetEnumerator () : IDictionaryEnumerator
Not applicable.

Return Value

An IDictionaryEnumerator for the DictionaryBase instance.

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. Reset also brings the enumerator back to this position. At this position, Current is undefined. Therefore, you must call MoveNext 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 its behavior is undefined.

The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

This method is an O(1) operation.

The following code example implements the DictionaryBase class and uses that implementation to create a dictionary of String keys and values that have a Length of 5 characters or less.

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

*/


import System.*;
import System.Collections.*;

public class ShortStringDictionary extends DictionaryBase
{
    /** @property 
     */
    public String get_Value(String key)
    {
        return((String)(get_Dictionary().get_Item(key)));
    } //get_Value

    /** @property 
     */
    public void set_Value(String key,String value)
    {
        get_Dictionary().set_Item(key, value);
    } //set_Value
   
   
    /** @property 
     */
    public ICollection get_Keys()
    {
        return get_Dictionary().get_Keys();
    } //get_Keys
   
    /** @property 
     */
    public ICollection get_Values()
    {
        return get_Dictionary().get_Values();
    } //get_Values
   
    public void Add(String key, String value) 
    {
        get_Dictionary().Add(key, value);
    } //Add
   
    public boolean Contains(String key) 
    {
        return get_Dictionary().Contains(key);
    } //Contains
   
    public void Remove(String key) 
    {
        get_Dictionary().Remove(key);
    } //Remove
   
    protected void OnInsert(Object key, Object value) 
    {
        if (!key.GetType().Equals(Type.GetType("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().Equals(Type.GetType("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");
            }
        }
    } //OnInsert
   
    protected void OnRemove(Object key, Object value) 
    {
        if (!key.GetType().Equals(Type.GetType("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");
            }
        }
    } //OnRemove
   
    protected void OnSet(Object key, Object oldValue, Object newValue) 
    {
        if (!key.GetType().Equals(Type.GetType("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().Equals(Type.GetType("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") ;
            }
        }
    } //OnSet
   
    protected void OnValidate(Object key, Object value) 
    {
        if (!key.GetType().Equals(Type.GetType("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().Equals(Type.GetType("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") ;
            }
        }
    } //OnValidate
} //ShortStringDictionary

public class SamplesDictionaryBase
{
    public static void main(String[] args)
    {
        // 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 while. This is the
        // preferred method.
        Console.WriteLine("Contents of the collection (using for):");
        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.
        boolean b = mySSC.Contains("Three");
        Console.Write("Contains \"Three\": ");
        Console.WriteLine(b);
        b = mySSC.Contains("Twelve");
        Console.Write("Contains \"Twelve\": ");
        Console.WriteLine(b);
        Console.WriteLine();
    
        // Removes an element from the collection.
        mySSC.Remove("Two");
    
        // Displays the contents of the collection.
        Console.WriteLine("After removing \"Two\":");
        PrintKeysAndValues1(mySSC);
    }//main
   
    // Uses the for statement which hides the complexity of the enumerator.
    // NOTE: The for statement is the preferred way of enumerating the 
    // contents of a collection.
    public static void PrintKeysAndValues1(ShortStringDictionary myCol) 
    {
        String strValue;
        String strKeys[] = new String[myCol.get_Count()];
        myCol.get_Keys().CopyTo(strKeys,0);

        for (int iCtr = 0; iCtr < myCol.get_Count(); iCtr++){
            strValue = myCol.get_Value(strKeys[iCtr]);
            Console.WriteLine("   {0,-5} : {1}", strKeys[iCtr], strValue);
        }
        Console.WriteLine();
    } //PrintKeysAndValues1
   
    // Uses the enumerator. 
    // NOTE: The for 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.get_Current()  != null  ) {
                myDE =((DictionaryEntry)(myEnumerator.get_Current()));
                Console.WriteLine("   {0,-5} : {1}", myDE.get_Key(), 
                myDE.get_Value());
            }
        }
        Console.WriteLine();
    } //PrintKeysAndValues2
   
    // Uses the Keys property and the Value property.
    public static void PrintKeysAndValues3(ShortStringDictionary myCol) 
    {
        ICollection myKeys = myCol.get_Keys();
        IEnumerator myEnumerator = myKeys.GetEnumerator();
        while (myEnumerator.MoveNext()) {
            String k = myEnumerator.get_Current().ToString();
            Console.WriteLine("   {0,-5} : {1}", k, myCol.get_Item(k));
        }
        Console.WriteLine();
    } //PrintKeysAndValues3
} //SamplesDictionaryBase
 
/* 
This code produces the following output.

Contents of the collection (using while):
   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

*/


Windows 98, Windows Server 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

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

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