Information
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

Collection Class

A Visual Basic Collection is an ordered set of items that can be referred to as a unit.

System.Object
  Microsoft.VisualBasic.Collection

Namespace:  Microsoft.VisualBasic
Assembly:  Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)

[DebuggerDisplayAttribute("Count = {Count}")]
[DefaultMemberAttribute("Item")]
public sealed class Collection : IEnumerable, 
	ICollection, IList

The Collection type exposes the following members.

  NameDescription
Public methodCollectionCreates and returns a new Visual Basic Collection object.
Top

  NameDescription
Public propertyCountReturns an Integer containing the number of elements in a collection. Read-only.
Public propertyItem[Int32]Returns a specific element of a Collection object either by position or by key. Read-only.
Public propertyItem[Object]Returns a specific element of a Collection object either by position or by key. Read-only.
Public propertyItem[String]Returns a specific element of a Collection object either by position or by key. Read-only.
Top

  NameDescription
Public methodAddAdds an element to a Collection object.
Public methodClearDeletes all elements of a Visual Basic Collection object.
Public methodContainsReturns a Boolean value indicating whether a Visual Basic Collection object contains an element with a specific key.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetEnumeratorReturns a reference to an enumerator object, which is used to iterate over a Collection object.
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodRemove(Int32)Removes an element from a Collection object.
Public methodRemove(String)Removes an element from a Collection object.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Top

  NameDescription
Public Extension MethodAsQueryableConverts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodCast<TResult>Converts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodOfType<TResult>Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
Top

  NameDescription
Explicit interface implemetationPrivate methodICollection.CopyToCopies the elements of the Collection to an Array, starting at a particular Array index. Implements the ICollection interface.
Explicit interface implemetationPrivate propertyICollection.CountGets the number of items in this collection. Implements the ICollection interface.
Explicit interface implemetationPrivate propertyICollection.IsSynchronizedGets a value indicating whether access to the Collection object is synchronized (thread safe). Implements the ICollection interface.
Explicit interface implemetationPrivate propertyICollection.SyncRootGets an object that can be used to synchronize access to the Collection object. Implements the ICollection interface.
Explicit interface implemetationPrivate methodIEnumerable.GetEnumeratorReturns an enumerator that iterates through the collection. Implements the ICollection interface.
Explicit interface implemetationPrivate methodIList.AddAdds an item to the Collection object. Implements the IList interface.
Explicit interface implemetationPrivate methodIList.ClearRemoves all items from the Collection object. Implements the IList interface.
Explicit interface implemetationPrivate methodIList.ContainsDetermines whether the Collection object contains a specific value. Implements the IList interface.
Explicit interface implemetationPrivate methodIList.IndexOfDetermines the index of a specific item in the Collection object. Implements the IList interface.
Explicit interface implemetationPrivate methodIList.InsertInserts an item to the Collection object at the specified index. Implements the IList interface.
Explicit interface implemetationPrivate propertyIList.IsFixedSizeGets a value indicating whether the Collection object has a fixed size. Implements the IList interface.
Explicit interface implemetationPrivate propertyIList.IsReadOnlyGets a value indicating whether the Collection object is read-only. Implements the IList interface.
Explicit interface implemetationPrivate propertyIList.ItemGets or sets the element at the specified index. Implements the IList interface
Explicit interface implemetationPrivate methodIList.RemoveRemoves the first occurrence of a specific object from the Collection object. Implements the IList interface.
Explicit interface implemetationPrivate methodIList.RemoveAtRemoves the Collection object item at the specified index. Implements the IList interface.
Top

The Visual Basic Collection object provides a convenient way to refer to a related group of items as a single object. The items, or elements, in a collection need only be related by the fact that they exist in the collection. Elements of a collection do not have to share the same data type.

You can create a collection the same way you create other objects, as the following example illustrates.

Dim coll As New Microsoft.VisualBasic.Collection()

Once you have created a collection, you can do any of the following:

  • Add an element by using the Add method.

  • Remove an element by using the Remove method.

  • Remove all elements by using the Clear method.

  • Find out how many elements the collection contains by using the Count property.

  • Check whether a specific element is present by using the Contains method.

  • Return a specific element from the collection by using the Item property.

  • Iterate through the entire collection by using a For Each...Next loop.

    NoteNote:

    Although the Visual Basic Collection object has functionality identical to the Collection object in Visual Basic 6.0, the two cannot interoperate in a COM environment.

    Caution noteCaution:

    Iterating through a Visual Basic Collection is not a thread-safe procedure. Even if the collection is synchronized, other threads can still modify the collection, causing the enumerator to throw an exception. To guarantee thread safety during enumeration, either lock the collection or catch the exceptions resulting from changes made by other threads. For more information about locking a programming element, see the Visual Basic documentation about the SyncLock statement. 

The following example creates the Collection object names and a dialog box with which a user can add objects (names) to the collection. It then displays the names in the collection, and finally empties the collection without disposing of the Collection object itself.

To see how this works, choose the Add Class command from the Project menu and declare a public variable called instanceName at the module level of nameClass (type Public instanceName) to hold the names of each instance. Leave the default name as nameClass. Copy and paste the following code into the General section of another module, and then start it with the statement classNamer in another procedure. (This example works only with host applications that support classes.)


Public Class nameClass
    Public instanceName As String
End Class
Sub classNamer()
  ' Create a Visual Basic Collection object.
  Dim names As New Microsoft.VisualBasic.Collection()
  Dim key As Integer
  Dim msg As String
  Dim name As String
  Dim nameList As String = ""
  ' 1. Get names from the user to add to the collection.
  Do
    Dim inst As New nameClass()
    key += 1
    name = "SampleCollectionItems"
    inst.instanceName = name
    ' If user entered a name, add it to the collection.
    If inst.instanceName <> "" Then
      names.Add(inst, CStr(key))
    End If
  Loop Until name = ""
  ' 2. Create and display a list of names from the collection.
  For Each oneInst As nameClass In names
    nameList &= oneInst.instanceName & vbCrLf
  Next oneInst
  msg = nameList
  ' 3. Remove elements from the collection without disposing of the collection.
  For count As Integer = 1 To names.Count
    names.Remove(1)
    ' Since Visual Basic collections are reindexed automatically, 
    ' remove the first member on each iteration.
  Next count
End Sub


Silverlight

Supported in: 5, 4, 3

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
Was this page helpful?
(1500 characters remaining)
Thank you for your feedback

Community Additions

Show:
© 2014 Microsoft