IList Interface
Represents a non-generic collection of objects that can be individually accessed by index.
Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)
The IList type exposes the following members.
| Name | Description | |
|---|---|---|
![]() ![]() ![]() | Count | Gets the number of elements contained in the ICollection. (Inherited from ICollection.) |
![]() ![]() ![]() | IsFixedSize | Gets a value indicating whether the IList has a fixed size. |
![]() ![]() ![]() | IsReadOnly | Gets a value indicating whether the IList is read-only. |
![]() ![]() ![]() | IsSynchronized | Gets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.) |
![]() ![]() ![]() | Item | Gets or sets the element at the specified index. |
![]() ![]() ![]() | SyncRoot | Gets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.) |
| Name | Description | |
|---|---|---|
![]() ![]() ![]() | Add | Adds an item to the IList. |
![]() ![]() ![]() | Clear | Removes all items from the IList. |
![]() ![]() ![]() | Contains | Determines whether the IList contains a specific value. |
![]() ![]() ![]() | CopyTo | Copies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.) |
![]() ![]() ![]() | GetEnumerator | Returns an enumerator that iterates through a collection. (Inherited from IEnumerable.) |
![]() ![]() ![]() | IndexOf | Determines the index of a specific item in the IList. |
![]() ![]() ![]() | Insert | Inserts an item to the IList at the specified index. |
![]() ![]() ![]() | Remove | Removes the first occurrence of a specific object from the IList. |
![]() ![]() ![]() | RemoveAt | Removes the IList item at the specified index. |
| Name | Description | |
|---|---|---|
![]() ![]() | AsQueryable | Converts an IEnumerable to an IQueryable. (Defined by Queryable.) |
![]() ![]() ![]() | Cast(Of TResult) | Converts the elements of an IEnumerable to the specified type. (Defined by Enumerable.) |
![]() ![]() ![]() | OfType(Of TResult) | Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.) |
IList is a descendant of the ICollection interface and is the base interface of all non-generic lists. IList implementations fall into three categories: read-only, fixed-size, and variable-size. A read-only IList cannot be modified. A fixed-size IList does not allow the addition or removal of elements, but it allows the modification of existing elements. A variable-size IList allows the addition, removal, and modification of elements.
For the generic version of this interface, see System.Collections.Generic.IList(Of T).
The following example demonstrates the implementation of the IList interface to create a simple list, fixed-size list.
Note: |
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To run this example, see Building Examples That Use a Demo Method and a TextBlock Control. |
Imports System.Collections Public Class Example Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock) Dim myList As New SimpleList() ' Populate the List outputBlock.Text &= "Populate the List" & vbCrLf myList.Add("one") myList.Add("two") myList.Add("three") myList.Add("four") myList.Add("five") myList.Add("six") myList.Add("seven") myList.Add("eight") myList.PrintContents(outputBlock) outputBlock.Text &= vbCrLf ' Remove elements from the list outputBlock.Text &= "Remove elements from the list" & vbCrLf myList.Remove("six") myList.Remove("eight") myList.PrintContents(outputBlock) outputBlock.Text &= vbCrLf ' Add an element to the end of the list outputBlock.Text &= "Add an element to the end of the list" & vbCrLf myList.Add("nine") myList.PrintContents(outputBlock) outputBlock.Text &= vbCrLf ' Insert an element into the middle of the list outputBlock.Text &= "Insert an element into the middle of the list" & vbCrLf myList.Insert(4, "number") myList.PrintContents(outputBlock) outputBlock.Text &= vbCrLf ' Check for specific elements in the list outputBlock.Text &= "Check for specific elements in the list" & vbCrLf outputBlock.Text += String.Format("List contains 'three': {0}", myList.Contains("three")) & vbCrLf outputBlock.Text += String.Format("List contains 'ten': {0}", myList.Contains("ten")) & vbCrLf End Sub End Class ' class Program Public Class SimpleList Implements IList Private _contents(8) As Object Private _count As Integer Public Sub New() _count = 0 End Sub ' IList Members Public Function Add(ByVal value As Object) As Integer Implements IList.Add If (_count < _contents.Length - 1) Then _contents(_count) = value _count = _count + 1 Return (_count - 1) Else Return -1 End If End Function Public Sub Clear() Implements IList.Clear _count = 0 End Sub Public Function Contains(ByVal value As Object) As Boolean Implements IList.Contains Dim inList As Boolean = False Dim i As Integer For i = 0 To Count If _contents(i) = value Then inList = True Exit For End If Next i Return inList End Function Public Function IndexOf(ByVal value As Object) As Integer Implements IList.IndexOf Dim itemIndex As Integer = -1 Dim i As Integer For i = 0 To Count If _contents(i) = value Then itemIndex = i Exit For End If Next i Return itemIndex End Function Public Sub Insert(ByVal index As Integer, ByVal value As Object) Implements IList.Insert If (_count + 1) <= (_contents.Length - 1) And (index < Count) And (index >= 0) Then _count = _count + 1 Dim i As Integer For i = Count - 1 To index _contents(i) = _contents(i - 1) Next i _contents(index) = value End If End Sub Public ReadOnly Property IsFixedSize() As Boolean Implements IList.IsFixedSize Get Return True End Get End Property Public ReadOnly Property IsReadOnly() As Boolean Implements IList.IsReadOnly Get Return False End Get End Property Public Sub Remove(ByVal value As Object) Implements IList.Remove RemoveAt(IndexOf(value)) End Sub Public Sub RemoveAt(ByVal index As Integer) Implements IList.RemoveAt If index >= 0 And index < Count Then Dim i As Integer For i = index To Count - 1 _contents(i) = _contents(i + 1) Next i _count = _count - 1 End If End Sub Public Property Item(ByVal index As Integer) As Object Implements IList.Item Get Return _contents(index) End Get Set(ByVal value As Object) _contents(index) = value End Set End Property ' ICollection Members Public Sub CopyTo(ByVal array As Array, ByVal index As Integer) Implements ICollection.CopyTo Dim j As Integer = index Dim i As Integer For i = 0 To Count array.SetValue(_contents(i), j) j = j + 1 Next i End Sub Public ReadOnly Property Count() As Integer Implements ICollection.Count Get Return _count End Get End Property Public ReadOnly Property IsSynchronized() As Boolean Implements ICollection.IsSynchronized Get Return False End Get End Property ' Return the current instance since the underlying store is not ' publicly available. Public ReadOnly Property SyncRoot() As Object Implements ICollection.SyncRoot Get Return Me End Get End Property ' IEnumerable Members Public Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator ' Refer to the IEnumerator documentation for an example of ' implementing an enumerator. Throw New Exception("The method or operation is not implemented.") End Function Public Sub PrintContents(ByVal outputBlock As System.Windows.Controls.TextBlock) outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length - 1, _count) & vbCrLf outputBlock.Text &= "List contents:" Dim i As Integer For i = 0 To Count outputBlock.Text += String.Format(" {0}", _contents(i)) Next i outputBlock.Text &= vbCrLf End Sub End Class ' This code produces output similar to the following: ' Populate the List: ' List has a capacity of 8 and currently has 8 elements. ' List contents: one two three four five six seven eight ' ' Remove elements from the list: ' List has a capacity of 8 and currently has 6 elements. ' List contents: one two three four five seven ' ' Add an element to the end of the list: ' List has a capacity of 8 and currently has 7 elements. ' List contents: one two three four five seven nine ' ' Insert an element into the middle of the list: ' List has a capacity of 8 and currently has 8 elements. ' List contents: one two three four number five seven nine ' ' Check for specific elements in the list: ' List contains "three": True ' List contains "ten": False
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