A Visual Basic Collection is an ordered set of items that can be referred to as a unit.
Assembly: Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)
Thetype exposes the following members.
|Count||Returns an Integer containing the number of elements in a collection. Read-only.|
|Item[Int32]||Returns a specific element of a Collection object either by position or by key. Read-only.|
|Item[Object]||Returns a specific element of a Collection object either by position or by key. Read-only.|
|Item[String]||Returns a specific element of a Collection object either by position or by key. Read-only.|
|Add||Adds an element to a Collection object.|
|Clear||Deletes all elements of a Visual Basic Collection object.|
|Contains||Returns a Boolean value indicating whether a Visual Basic Collection object contains an element with a specific key.|
|Equals(Object)||Determines whether the specified Object is equal to the current Object. (Inherited from Object.)|
|Finalize||Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)|
|GetEnumerator||Returns a reference to an enumerator object, which is used to iterate over a object.|
|GetHashCode||Serves as a hash function for a particular type. (Inherited from Object.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|Remove(Int32)||Removes an element from a Collection object.|
|Remove(String)||Removes an element from a Collection object.|
|ToString||Returns a string that represents the current object. (Inherited from Object.)|
|ICollection.CopyTo||Copies the elements of the to an Array, starting at a particular Array index. Implements the ICollection interface.|
|ICollection.Count||Gets the number of items in this collection. Implements the ICollection interface.|
|ICollection.IsSynchronized||Gets a value indicating whether access to the object is synchronized (thread safe). Implements the ICollection interface.|
|ICollection.SyncRoot||Gets an object that can be used to synchronize access to the object. Implements the ICollection interface.|
|IEnumerable.GetEnumerator||Returns an enumerator that iterates through the collection. Implements the ICollection interface.|
|IList.Add||Adds an item to the object. Implements the IList interface.|
|IList.Clear||Removes all items from the object. Implements the IList interface.|
|IList.Contains||Determines whether the object contains a specific value. Implements the IList interface.|
|IList.IndexOf||Determines the index of a specific item in the object. Implements the IList interface.|
|IList.Insert||Inserts an item to the object at the specified index. Implements the IList interface.|
|IList.IsFixedSize||Gets a value indicating whether the object has a fixed size. Implements the IList interface.|
|IList.IsReadOnly||Gets a value indicating whether the object is read-only. Implements the IList interface.|
|IList.Item||Gets or sets the element at the specified index. Implements the IList interface|
|IList.Remove||Removes the first occurrence of a specific object from the object. Implements the IList interface.|
|IList.RemoveAt||Removes the object item at the specified index. Implements the IList interface.|
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.
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.
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
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