DictionaryBase.OnSet Method
Assembly: mscorlib (in mscorlib.dll)
protected void OnSet ( Object key, Object oldValue, Object newValue )
protected function OnSet ( key : Object, oldValue : Object, newValue : Object )
Not applicable.
Parameters
- key
The key of the element to locate.
- oldValue
The old value of the element associated with key.
- newValue
The new value of the element associated with key.
The default implementation of this method is intended to be overridden by a derived class to perform some action before the specified element is set.
The On* methods are invoked only on the instance returned by the Dictionary property, but not on the instance returned by the InnerHashtable property.
The default implementation of this method is an O(1) operation.
Notes to Implementers: This method allows implementers to define processes that must be performed before setting the specified element in the underlying System.Collections.Hashtable. By defining this method, implementers can add functionality to inherited methods without having to override all other methods. OnSet is invoked before the standard Set behavior, whereas OnSetComplete is invoked after the standard Set behavior. For example, implementers can restrict which values can be overwritten by performing a check inside OnSet.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.