DictionaryBase Class
Provides the abstract base class for a strongly typed collection of key/value pairs.
Assembly: mscorlib (in mscorlib.dll)
The foreach statement of the C# language (for each in Visual Basic) requires the type of each element in the collection. Since each element of the DictionaryBase is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry.
The foreach statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.
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Because keys can be inherited and their behavior changed, their absolute uniqueness cannot be guaranteed by comparisons using the Equals method. |
This base class is provided to make it easier for implementers to create a strongly typed custom collection. Implementers are encouraged to extend this base class instead of creating their own.
Members of this base class are protected and are intended to be used through a derived class only.
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.
Imports System Imports System.Collections Public Class ShortStringDictionary Inherits DictionaryBase Default Public Property Item(key As String) As String Get Return CType(Dictionary(key), String) End Get Set Dictionary(key) = value End Set End Property Public ReadOnly Property Keys() As ICollection Get Return Dictionary.Keys End Get End Property Public ReadOnly Property Values() As ICollection Get Return Dictionary.Values End Get End Property Public Sub Add(key As String, value As String) Dictionary.Add(key, value) End Sub 'Add Public Function Contains(key As String) As Boolean Return Dictionary.Contains(key) End Function 'Contains Public Sub Remove(key As String) Dictionary.Remove(key) End Sub 'Remove Protected Overrides Sub OnInsert(key As Object, value As Object) If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then Throw New ArgumentException("key must be of type String.", "key") Else Dim strKey As String = CType(key, String) If strKey.Length > 5 Then Throw New ArgumentException("key must be no more than 5 characters in length.", "key") End If End If If Not GetType(System.String).IsAssignableFrom(value.GetType()) Then Throw New ArgumentException("value must be of type String.", "value") Else Dim strValue As String = CType(value, String) If strValue.Length > 5 Then Throw New ArgumentException("value must be no more than 5 characters in length.", "value") End If End If End Sub 'OnInsert Protected Overrides Sub OnRemove(key As Object, value As Object) If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then Throw New ArgumentException("key must be of type String.", "key") Else Dim strKey As String = CType(key, String) If strKey.Length > 5 Then Throw New ArgumentException("key must be no more than 5 characters in length.", "key") End If End If End Sub 'OnRemove Protected Overrides Sub OnSet(key As Object, oldValue As Object, newValue As Object) If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then Throw New ArgumentException("key must be of type String.", "key") Else Dim strKey As String = CType(key, String) If strKey.Length > 5 Then Throw New ArgumentException("key must be no more than 5 characters in length.", "key") End If End If If Not GetType(System.String).IsAssignableFrom(newValue.GetType()) Then Throw New ArgumentException("newValue must be of type String.", "newValue") Else Dim strValue As String = CType(newValue, String) If strValue.Length > 5 Then Throw New ArgumentException("newValue must be no more than 5 characters in length.", "newValue") End If End If End Sub 'OnSet Protected Overrides Sub OnValidate(key As Object, value As Object) If Not GetType(System.String).IsAssignableFrom(key.GetType()) Then Throw New ArgumentException("key must be of type String.", "key") Else Dim strKey As String = CType(key, String) If strKey.Length > 5 Then Throw New ArgumentException("key must be no more than 5 characters in length.", "key") End If End If If Not GetType(System.String).IsAssignableFrom(value.GetType()) Then Throw New ArgumentException("value must be of type String.", "value") Else Dim strValue As String = CType(value, String) If strValue.Length > 5 Then Throw New ArgumentException("value must be no more than 5 characters in length.", "value") End If End If End Sub 'OnValidate End Class 'ShortStringDictionary Public Class SamplesDictionaryBase Public Shared Sub Main() ' Creates and initializes a new DictionaryBase. Dim mySSC As New ShortStringDictionary() ' Adds elements to the collection. mySSC.Add("One", "a") mySSC.Add("Two", "ab") mySSC.Add("Three", "abc") mySSC.Add("Four", "abcd") mySSC.Add("Five", "abcde") ' Display the contents of the collection using For Each. This is the preferred method. Console.WriteLine("Contents of the collection (using For Each):") PrintKeysAndValues1(mySSC) ' Display the contents of the collection using the enumerator. Console.WriteLine("Contents of the collection (using enumerator):") PrintKeysAndValues2(mySSC) ' Display the contents of the collection using the Keys property and the Item property. Console.WriteLine("Initial contents of the collection (using Keys and Item):") PrintKeysAndValues3(mySSC) ' Tries to add a value that is too long. Try mySSC.Add("Ten", "abcdefghij") Catch e As ArgumentException Console.WriteLine(e.ToString()) End Try ' Tries to add a key that is too long. Try mySSC.Add("Eleven", "ijk") Catch e As ArgumentException Console.WriteLine(e.ToString()) End Try Console.WriteLine() ' Searches the collection with Contains. Console.WriteLine("Contains ""Three"": {0}", mySSC.Contains("Three")) Console.WriteLine("Contains ""Twelve"": {0}", mySSC.Contains("Twelve")) Console.WriteLine() ' Removes an element from the collection. mySSC.Remove("Two") ' Displays the contents of the collection. Console.WriteLine("After removing ""Two"":") PrintKeysAndValues1(mySSC) End Sub 'Main ' Uses the For Each statement which hides the complexity of the enumerator. ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. Public Shared Sub PrintKeysAndValues1(myCol As ShortStringDictionary) Dim myDE As DictionaryEntry For Each myDE In myCol Console.WriteLine(" {0,-5} : {1}", myDE.Key, myDE.Value) Next myDE Console.WriteLine() End Sub 'PrintKeysAndValues1 ' Uses the enumerator. ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. Public Shared Sub PrintKeysAndValues2(myCol As ShortStringDictionary) Dim myDE As DictionaryEntry Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator() While myEnumerator.MoveNext() If Not (myEnumerator.Current Is Nothing) Then myDE = CType(myEnumerator.Current, DictionaryEntry) Console.WriteLine(" {0,-5} : {1}", myDE.Key, myDE.Value) End If End While Console.WriteLine() End Sub 'PrintKeysAndValues2 ' Uses the Keys property and the Item property. Public Shared Sub PrintKeysAndValues3(myCol As ShortStringDictionary) Dim myKeys As ICollection = myCol.Keys Dim k As String For Each k In myKeys Console.WriteLine(" {0,-5} : {1}", k, myCol(k)) Next k Console.WriteLine() End Sub 'PrintKeysAndValues3 End Class 'SamplesDictionaryBase 'This code produces the following output. ' 'Contents of the collection (using For Each): ' Three : abc ' Five : abcde ' Two : ab ' One : a ' Four : abcd ' 'Contents of the collection (using enumerator): ' Three : abc ' Five : abcde ' Two : ab ' One : a ' Four : abcd ' 'Initial contents of the collection (using Keys and Item): ' Three : abc ' Five : abcde ' Two : ab ' One : a ' Four : abcd ' 'System.ArgumentException: value must be no more than 5 characters in length. 'Parameter name: value ' at ShortStringDictionary.OnValidate(Object key, Object value) ' at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value) ' at SamplesDictionaryBase.Main() 'System.ArgumentException: key must be no more than 5 characters in length. 'Parameter name: key ' at ShortStringDictionary.OnValidate(Object key, Object value) ' at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value) ' at SamplesDictionaryBase.Main() ' 'Contains "Three": True 'Contains "Twelve": False ' 'After removing "Two": ' Three : abc ' Five : abcde ' One : a ' Four : abcd
System.Collections.DictionaryBase
System.Diagnostics.InstanceDataCollection
System.Diagnostics.InstanceDataCollectionCollection
System.DirectoryServices.ActiveDirectory.ActiveDirectoryReplicationMetadata
System.DirectoryServices.Protocols.SearchResultAttributeCollection
System.DirectoryServices.ResultPropertyCollection
System.Web.Services.Discovery.DiscoveryClientDocumentCollection
System.Web.Services.Discovery.DiscoveryClientReferenceCollection
System.Web.Services.Discovery.DiscoveryExceptionDictionary
Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
This implementation does not provide a synchronized (thread-safe) wrapper for a DictionaryBase, but derived classes can create their own synchronized versions of the DictionaryBase using the SyncRoot property.
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.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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