CollectionBase.OnValidate Method (Object)
Performs additional custom processes when validating a value.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- value
-
Type:
System.Object
The object to validate.
| Exception | Condition |
|---|---|
| ArgumentNullException | value is null. |
The default implementation of this method determines whether value is null, and, if so, throws ArgumentNullException. It is intended to be overridden by a derived class to perform additional action when the specified element is validated.
The On* methods are invoked only on the instance returned by the List property, but not on the instance returned by the InnerList 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 when executing the standard behavior of the underlying System.Collections.ArrayList. By defining this method, implementers can add functionality to inherited methods without having to override all other methods.
OnValidate can be used to impose restrictions on the type of objects that are accepted into the collection. The default implementation prevents null from being added to or removed from the underlying System.Collections.ArrayList.
OnValidate is called prior to OnInsert, OnRemove, and OnSet.
The following code example implements the CollectionBase class and uses that implementation to create a collection of Int16 objects.
Imports System Imports System.Collections Public Class Int16Collection Inherits CollectionBase Default Public Property Item(index As Integer) As Int16 Get Return CType(List(index), Int16) End Get Set List(index) = value End Set End Property Public Function Add(value As Int16) As Integer Return List.Add(value) End Function 'Add Public Function IndexOf(value As Int16) As Integer Return List.IndexOf(value) End Function 'IndexOf Public Sub Insert(index As Integer, value As Int16) List.Insert(index, value) End Sub 'Insert Public Sub Remove(value As Int16) List.Remove(value) End Sub 'Remove Public Function Contains(value As Int16) As Boolean ' If value is not of type Int16, this will return false. Return List.Contains(value) End Function 'Contains Protected Overrides Sub OnInsert(index As Integer, value As Object) ' Insert additional code to be run only when inserting values. End Sub 'OnInsert Protected Overrides Sub OnRemove(index As Integer, value As Object) ' Insert additional code to be run only when removing values. End Sub 'OnRemove Protected Overrides Sub OnSet(index As Integer, oldValue As Object, newValue As Object) ' Insert additional code to be run only when setting values. End Sub 'OnSet Protected Overrides Sub OnValidate(value As Object) If Not GetType(System.Int16).IsAssignableFrom(value.GetType()) Then Throw New ArgumentException("value must be of type Int16.", "value") End If End Sub 'OnValidate End Class 'Int16Collection Public Class SamplesCollectionBase Public Shared Sub Main() ' Creates and initializes a new CollectionBase. Dim myI16 As New Int16Collection() ' Adds elements to the collection. myI16.Add( 1 ) myI16.Add( 2 ) myI16.Add( 3 ) myI16.Add( 5 ) myI16.Add( 7 ) ' Display the contents of the collection using For Each. This is the preferred method. Console.WriteLine("Contents of the collection (using For Each):") PrintValues1(myI16) ' Display the contents of the collection using the enumerator. Console.WriteLine("Contents of the collection (using enumerator):") PrintValues2(myI16) ' Display the contents of the collection using the Count property and the Item property. Console.WriteLine("Initial contents of the collection (using Count and Item):") PrintIndexAndValues(myI16) ' Searches the collection with Contains and IndexOf. Console.WriteLine("Contains 3: {0}", myI16.Contains(3)) Console.WriteLine("2 is at index {0}.", myI16.IndexOf(2)) Console.WriteLine() ' Inserts an element into the collection at index 3. myI16.Insert(3, 13) Console.WriteLine("Contents of the collection after inserting at index 3:") PrintIndexAndValues(myI16) ' Gets and sets an element using the index. myI16(4) = 123 Console.WriteLine("Contents of the collection after setting the element at index 4 to 123:") PrintIndexAndValues(myI16) ' Removes an element from the collection. myI16.Remove(2) ' Display the contents of the collection using the Count property and the Item property. Console.WriteLine("Contents of the collection after removing the element 2:") PrintIndexAndValues(myI16) End Sub 'Main ' Uses the Count property and the Item property. Public Shared Sub PrintIndexAndValues(myCol As Int16Collection) Dim i As Integer For i = 0 To myCol.Count - 1 Console.WriteLine(" [{0}]: {1}", i, myCol(i)) Next i Console.WriteLine() End Sub 'PrintIndexAndValues ' 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 PrintValues1(myCol As Int16Collection) Dim i16 As Int16 For Each i16 In myCol Console.WriteLine(" {0}", i16) Next i16 Console.WriteLine() End Sub 'PrintValues1 ' Uses the enumerator. ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. Public Shared Sub PrintValues2(myCol As Int16Collection) Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator() While myEnumerator.MoveNext() Console.WriteLine(" {0}", myEnumerator.Current) End While Console.WriteLine() End Sub 'PrintValues2 End Class 'SamplesCollectionBase 'This code produces the following output. ' 'Contents of the collection (using For Each): ' 1 ' 2 ' 3 ' 5 ' 7 ' 'Contents of the collection (using enumerator): ' 1 ' 2 ' 3 ' 5 ' 7 ' 'Initial contents of the collection (using Count and Item): ' [0]: 1 ' [1]: 2 ' [2]: 3 ' [3]: 5 ' [4]: 7 ' 'Contains 3: True '2 is at index 1. ' 'Contents of the collection after inserting at index 3: ' [0]: 1 ' [1]: 2 ' [2]: 3 ' [3]: 13 ' [4]: 5 ' [5]: 7 ' 'Contents of the collection after setting the element at index 4 to 123: ' [0]: 1 ' [1]: 2 ' [2]: 3 ' [3]: 13 ' [4]: 123 ' [5]: 7 ' 'Contents of the collection after removing the element 2: ' [0]: 1 ' [1]: 3 ' [2]: 13 ' [3]: 123 ' [4]: 7
Available since 10
.NET Framework
Available since 1.1