ConditionalWeakTable(Of TKey, TValue).Add Method (TKey, TValue)
Adds a key to the table.
Assembly: mscorlib (in mscorlib.dll)
| Exception | Condition |
|---|---|
| ArgumentNullException | key is null. |
| ArgumentException | key already exists. |
Every key in a ConditionalWeakTable(Of TKey, TValue) object must be unique. Keys are not unique if they refer to the same object (that is, if passing them as arguments to the Object.ReferenceEquals method returns true).
If the key is garbage-collected during the addition operation, the existing key/value pair is removed and the new key/value pair is added without an exception being thrown.
The following example defines a MainClass class and a MainInfo class, which provides information about the MainClass instance. The example then calls the Add method to add a MainClass object and its attached MainInfo object to a ConditionalWeakTable(Of TKey, TValue) table. The example also illustrates calls to the GetOrCreateValue and GetValue methods to add key/value pairs to the table, and to the TryGetValue method to retrieve the value of an existing key.
Imports System.Reflection Imports System.Runtime.CompilerServices Public Class Example Public Name As String Public Sub New(name As String) Me.Name = name End Sub Public Overrides Function ToString() As String Return Me.Name End Function End Class ' Define a class to contain information about each Example instance. Public Class ExampleInfo Public Name As String Public Methods As Integer Public Properties As Integer Public Overrides Function ToString() As String Return String.Format("{0}: {1} Methods, {2} Properties", _ Me.Name, Me.Methods, Me.Properties) End Function End Class Module TestExample Private flags As BindingFlags = BindingFlags.Public Or BindingFlags.Instance Public Sub Main() Dim ex1 As New Example("ex1") Dim ex2 As New Example("ex2") Dim ex3 As New Example("ex3") Dim exInfo1 As New ExampleInfo() exInfo1.Name = ex1.ToString() exInfo1.Methods = ex1.GetType().GetMethods(flags).Count exInfo1.Properties = ex1.GetType().GetProperties(flags).Count Dim exInfo3 As New ExampleInfo() exInfo3.Name = ex3.ToString() exInfo3.Methods = ex3.GetType().GetMethods(flags).Count exInfo3.Properties = ex3.GetType().GetProperties(flags).Count Dim attached As New ConditionalWeakTable(Of Example, ExampleInfo) Dim value As ExampleInfo = Nothing ' Attach a property to ex1 using the Add method, then retrieve it. attached.Add(ex1, exInfo1) If attached.TryGetValue(ex1, value) Then Console.WriteLine("{0}, {1}", ex1, value) Else Console.WriteLine("{0} does not have an attached property.", ex1) End If ' Attempt to retrieve the value attached to ex2. value = attached.GetValue(ex2, AddressOf TestExample.CreateAttachedValue) If attached.TryGetValue(ex2, value) Then Console.WriteLine("{0}, {1}", ex2, value) Else Console.WriteLine("{0} does not have an attached property.", ex2) End If ' Atttempt to retrieve the value attached to ex3. value = attached.GetOrCreateValue(ex3) Console.WriteLine("{0}, {1}", ex3, value) End Sub Public Function CreateAttachedValue(ex As Example) As ExampleInfo Dim info As New ExampleInfo() info.Name = ex.ToString() info.Methods = ex.GetType().GetMethods(flags).Count info.Properties = ex.GetType().GetProperties(flags).Count Return info End Function End Module ' The example displays the following output: ' ex1, ex1: 4 Methods, 0 Properties ' ex2, ex2: 4 Methods, 0 Properties ' ex3, : 0 Methods, 0 Properties
requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1